Overpotting

by Brent Walston

edited by Robert Potts

Introduction

Overpotting a bonsai tree into a container that is too large is a mistake that many bonsaists make unknowingly. The following is an explanation of why this is a problem. It is taken from several posts on the Bonsaisite Forums, by Brent Walston.
RP

Let's start with the physics

Water will drain from a pot until the lowest level of saturated soil (that can be supported) is reached. At this point drainage stops and this saturated layer remains saturated, no more water will drain out, ever. The height of this column of soil depends on the nature of the mix. A coarser soil will have a lower (shallower) column or layer of saturated soil than a finer mix. The total retained amount of water is less for a coarser soil.
Water can be removed from this saturated layer in two ways: evaporation (the water will be wicked upward as water evaporates from the surface), or by the absorption of water by the roots (powered by foliage transpiration). Of these two, removal by transpiration is by far the most effective. To prove this to yourself, just place two pots of identical soil next to each other, one with an established plant in it, the other with no plant. Water them thoroughly and then compare the weight of the pots over the period of one hot summer day.
If the plant is not root established, it cannot remove very much water by transpiration. This leaves too much water in the parts of soil without roots. In the short run, this is not much of a problem. In a proper environment, the plant will grow and will root establish quickly so that the saturated level is wicked dry in a day or two after a few weeks or months of growth.
However, if the pot is so large that the saturated level cannot be removed by normal root colonization, problems begin. This is not dependent on the soil type. With coarse soils a larger pot could be tolerated, but there are still limits to the space that can be quickly root colonized.

What happens if the limits are exceeded?

If you are using an organic amendment such as bark, you will experience accelerated soil composting. This means that you will lose your effective soil particle size more quickly than if you used a smaller pot which is wicked dry daily. This is the most common effect. You use a pot that is too large and it stays too wet. The organic amendment quickly decays in this wet environment, particle size decreases, soil collapses, the saturated level increases, even more water is retained, roots eventually remain in standing water, root failure occurs with, or without, the presence of a pathogen. Using only stable inorganic amendments would avoid this scenario, but there are other problems.
Even if the above doesn't occur, what kind of root growth occurs in a volume that is not wicked dry daily? When you water properly, a new charge of air is pulled into the pot by the volume of water draining from the drain holes. Carbon dioxide and other gases are purged from the soil. The longer you leave these gases in the soil, and the longer you wait to introduce a fresh charge of oxygen, the poorer the roots will be. If you create a situation such as overpotting that doesn't require daily watering, then you don't obtain an optimal soil growing environment.

And finally

The best environment is a soil that dries out daily. The best potting practice is to shift to the next larger size pot after each time the plant becomes root established as evidenced by forming an intact rootball. UC Davis studies have shown this, and I have conducted my own studies with Acer palmatum, which have verified it to my own satisfaction. It is not a marginal effect; the resulting growth improvement is significant.

Pruning and Pinching

by Brent Walston

Introduction

Pruning and pinching deciduous plants is an integral part of bonsai. It is how we create and maintain the fine branch structure and the pleasing outline that is essential to the beauty of the plant. Most people learn how to do this by rote, not really understanding the growth principles behind the methods they practice. This article explains in inexcruciating detail the why of pinching and pruning.

Pinching versus Pruning

First, let's discuss the role of 'pinching' as opposed to 'pruning'. Pruning is used (with reference to branches) to shape the branch, change the direction of the branch, and create taper within the branch. This is all done by pruning back to a bud aimed in the direction that you want it to go. This is usually done to a shoot with several internodes to be removed or with a larger lignified (woody) existing branch. It doesn't matter if you use concave cutters, your fingers, pruners, or chain saw, as long as you do a neat job.
Pinching can achieve the above for very small branches on some species, but for the most part, when we speak of pinching, we are talking about achieving ramification, or twigginess. When pinching the scaffolding of the branch is complete, it only needs detail work or ramification. This is done by removing the tip of the growing branch, usually removing two nodes of a three node shoot (a node is where buds appear or leaves grow). This does two things: 1) it shortens the branch. 2) it releases the buds behind it, interrupting apical dominance. The buds are held from opening by the release of a hormone (auxin) manufactured by the last (terminal) bud. Now the remaining bud is free to open and the buds behind this one.
The result is that by pinching out the terminal bud, or removing a two or three bud shoot, several of the buds remaining on this stem are free to open. Usually one or two will open before the new terminal bud starts forming the hormone and stops the process. Thus, where you once had a soft straight shoot with increasinginternodes (usually), you now have two buds opening forming a forked branch with shorter internodes and achieving ramification.

Achieving Shorter Internodes

I emphasized increasing above, because what most people have never bothered to observe (at least I never see it mentioned) is that the first two or three internodes of a released bud (achieved by pruning) are shorter than the internodes of the rest of the expanding shoot. By pinching back to one or two buds, we take advantage of this phenomenon, keeping the short internodes sections and discarding the strong shoot with the longer internodes. This is most important as we reach the outer portions of the branch which, like the branches on the trunk itself, should have leaves and nodes closer together as we approach the extremities.
Internode length is also influenced by the season and growth rate. Recently repotted plants will form longer internodes. Plants heavily fertilized in the spring, or pruned in the winter will also form longer internodes. Plants fertilized and/or pruned in early summer (but not spring), will form shorter internodes.
Armed with this knowledge, you will be able figure out how to achieve your goal. But of course you have to know what your goal is, and that is always the most difficult part, especially for beginners, who have not seen enough trees to know what they want to do.

Alternate versus Opposite

In addition to this, some knowledge of the species is important, because not all woody species react in the same way to pruning (although in general they do). There is also the major distinction that divides the woody species, those that have alternate leaves (buds), and those that have opposite. Alternate species are in general easier to work with, since the last bud will open before the one before it. This creates a strong main branch extension from the last bud and a weaker, smaller branch fork (secondary) from the next to last bud. Just keep this in mind and nature will do the rest.
In opposite species, the two buds are directly opposite each other and will often open simultaneously with equal strength. If not corrected this will give a fan pattern rather than a strong branch, weak secondary pattern usually desired for bonsai. If one bud is nipped out as they expand, one can mimic an alternate species. The same thing is achieved in the training of Black Pine, where great care is taken to make sure that all the branches fork, whereas in nature they would form whorls. Only after many years of wear and tear would they be reduced to forked branches.

Creating Branches

You must form a branch before you can ramify it. It doesn't matter how many internodes are in the first section of the branch, the only thing that matters is whether the branch will sprout from where you cut it to form a bend or create a secondary (side branch) and a new main extension. In general, if you remove the end of a branch, or otherwise prune it, you will change its direction, since a bud on the side of the branch will break and start the new extension in a different direction. The same is true for chopping the trunk. If you want a straight branch, don't prune it. Pinching buds at the end of the branch, means just that. Remove the one terminal (and its leaf) and leave the other buds and leaves alone. The bud at base of the next leaf will be the first to open and form a new shoot in a new direction. The rest of the branch may or may not have leaves, it is of no concern to us here. A branch for pinching purposes constitutes one straight section, or twig, with buds and possibly leaves but with no side branches. Each branch, twig, or shoot if you prefer has only one terminal bud, at the very end of the shoot.

Consider the Species

The other thing that you need to know, is how each species grow. For example, how Ulmus parvifolia grows in response to pruning. This species is dense with dormant buds embedded in the bark as well as the single bud contained in the leaf axil. When you prune this species, you get branches all over the place. This is the beauty of this species for bonsai, and also the reason I tell folks not to worry about branches until the trunk is formed, since you can easily get branches wherever you want them by simply pruning it hard.
Pruning this species hard will give you a little fuzz ball of branches. These are very soft and succulent, and there are very many more than you need. If you begin to prune them off as they emerge you weaken the plant and many of them will die back. Let them grow out about six to eight inches, or more, so they can harden and have a better chance of surviving. Then you can remove the ones you don't want and start thinking about what to do with the ones remaining. If you want one to fork at a certain location, prune it there. You can see that you must have an image of the tree that you want to obtain before you can proceed.
One the other end of the spectrum you have species like beech, Fagus, that have strongly determinate buds. Beech will usually only form one set of buds and leaves a year, although an occasional hard pruning will force dormant buds to break. Since you can't rely upon buds breaking wherever you want them, you must plan ahead and rely upon pinching as your main tool of branch formation as well as for ramification.

And finally

In a beginning bonsai book, you might get the advice, "let a shoot grow three sets of leaves and pinch it back to one or two". While this, in fact, may be good advice, you can see from the above that it's not quite that simple. Knowledge is power.

Nursery Shopping for Bonsai Material

by Brent Walston

Introduction

I used to go to nurseries all the time in search of material for bonsai. Now I just go out to the growing grounds and pick up whatever strikes my fancy. I could never completely work it all by myself in a hundred years. For most of you, nursery shopping for potential bonsai material will be the way that you acquire your collection. The following article offers some guidelines for effective shopping, or what to look for.

First, don't be afraid to get dirt on your hands and knees. I can always tell the real aficionados by how much dirt they get on their knees grubbing around the surface of the pot looking for a good nebari or trunk characteristic. The foliage and the branches are of our little importance, in most cases they will be discarded anyhow.
Look for a good nebari, the crown and surface roots of the plant. This is the single hardest element to obtain, if a tree has a good nebari and nothing else to offer, buy it, grow a trunk, then grow branches. Nobody said this was going to happen overnight. Look for a radical swelling at the base that soars into a tapered trunk. Look for surface roots that smoothly merge into this crown. The roots should come out radially. Circular roots can be problem and usually will have to be discarded.
If a tree lacks a good nebari, it still may offer other qualities too good to pass up. The second element to look for is a good trunk. Traditional 'masculine' trees will have thick trunks and mature bark. The more taper you can get the better. A thick trunk with no taper can be dealt with, but one with taper is better. The usual rule for such trees is that the height of the tree will be six times the diameter of the trunk at the base. So already you must form some sort of picture in your head of what the final tree will look like. At least picture how tall it will be with this size trunk. Will this work? Is there a branch that can be bent upward for an apex? Can the top be broken and a jin apex carved? Will the tree need to be grown out some more before it has sufficient trunk or height? Trees with smaller trunk proportions are perfectly acceptable, they usually have a more feminine appearance, softer and more sinewy. It just depends what you want and what the tree has to offer.
If you are looking for immediate gratification, or pretty quick bonsai, you must analyze the branching. If this thing is going in a bonsai pot soon, under one year, then some existing branches must be used. The first branch is usually one third the height of the tree. Does the tree have such a branch? It should be one third or less than the diameter of the trunk at the point at which it is attached, or it will be too fat. Skinny branches can be grown out, fat branches are a serious problem and can only be solved over a number of years by growing out the trunk. Choosing or finding a second branch must also include a decision on the front and back of the tree. Usually the first two branches are at the left and right of the tree and slightly toward the front, they make an angle of somewhere around 120 degrees. The third or back branch is usually 120 degrees from the first or second branch but not directly behind the tree. The back branch may also be the second branch but only rarely the first. The other branches can usually be grown out later.
PATIENCE! Ok, you have analyzed the tree and it has good possibilities, buy it and take it home. If it is not spring with the sap running, you can go ahead and do some styling, remove unwanted branches, wire and bend others, remove some surface soil to expose the nebari, reduce the top. In general, have a good time. If it is an evergreen do not remove more than one half the foliage while playing with it. Slap your fingers if they itch to remove just one more little branch.
If it is deciduous and it is dormant, have at it. If it a species that buds back nicely, and most do, you can work it down to the trunk alone. Check with someone to make sure the species will support this. Beech, for instance, usually will not. If it is the growing season but not early spring you can easily remove half or more of the foliage with your manipulations. If it is less than six weeks until the end of the season wait until it goes dormant or you risk throwing new growth that will not have time to harden off.
What about the roots? My advise is to leave them alone. This is where beginners get into trouble. They work a plant too much, too soon, and it cannot support all the changes. Do as much top work as you can and leave it in the existing can or put it in a larger can without disturbing the roots if it needs to grow out some more. Wait for the next opportunity to do root work. You can continue to clip and trim and wire branches and have a good time watching your little tree progress. It will be very easy to care for because it has excess root capacity compared to the canopy. It will not dry out easily and it will be easy to water and fertilize.
If you worked on the top during the winter wait at least until the following fall to do root work. If you worked the top after the spring flush you can work the roots in the fall, but it would be safer to wait until the following late winter or early spring. If you work on the top during the summer wait until the following fall. In other words give the plant an entire growth cycle before root pruning. I have used this formula many times and it has rarely failed me. Every time I lose a tree it is usually because I don't follow my own rules and do too much too fast. Learn to enjoy the tree in the nursery pot. I know the fascination for beginners is to get the tree in a little pot, but just having a tree in a pot is not bonsai.I have thousands of little trees in nursery pots and I enjoy them every bit as much as the ones in the bonsai pots.
Now that I have given you all the things to look for in nursery plants, I will try to make specific suggestions for what to do when you get to the nursery.
Take a plant species description book with you, do not rely on what the sales help tell you, unless you have dealt with this nursery before, and you know for a fact that they have honest, knowledgeable help. In the west any nursery worth its salt will have a copy of Sunset's Western Garden Book right on the counter for you to use, but it is better to take you own so you have it with you when you are actually looking at the plant.
If you live in the west you can use the maps in the front of 'Sunset' to find out what zone you live in to make proper plant choices according to cold hardiness and other factors. The 'Sunset' system is far to superior to USDA zones, and they do not correspond. Sunset's maps are much more detailed and consider far more information than the blanket USDA zones. If you don't live in the west take some time to read through this section to find the zone that most closely matches your area and use this number to aid in plant selection. Since the book includes zones from San Diego to the mountains of Washington almost the entire country should be able to find a comparable zone except the deep south and the upper Midwest.
Armed with this kind of information about plant material, you can make intelligent choices about the cold hardiness, watering requirements, and growth habits of any particular plant that strikes your fancy.
Since this is mostly for beginners, I suggest that you look for deciduous material, or hardier evergreens such as juniper. Stay away from pines unless you have several years of experience under your belt. Some may disagree with me, but I don't consider pines other than Pinus mugo to be beginner plants. Most pines in nurseries are already wrecked anyhow for bonsai.
For the most part stay with one gallon material since this will be inexpensive and no big deal if it succumbs to over ambitiousness. Also stay away from grafted material unless you know what to look for in grafts and the pitfalls of high grafts, ugly grafts, mismatches, etc (See the article on grafting for bonsai). Go for seedling material and cuttings. This will also be the least expensive material.
Bargain basement areas are often a great resource for bonsai shoppers. Here you will find the large trunked root bound material at good prices already dwarfed for you. However, pass up stuff that looks like it is on its last legs unless you have some experience. Take rootbound material home and immediately pot it up to the next larger size regardless of what size the final bonsai will be. This will insure the survival of the plant and invigorate the top, so you can do some work on it the following season. Do not overwork root bound material because it has no reserves, you must reinvigorate the plant first.
Look for plants with small leaves and twiggy branching, they will make the best bonsai candidates. In general stay away from plants with compound leaves. These are plants that have leaves that are usually large with many small leaflets. These plants will usually not ramify (create small twiggy branches).
If you want evergreens, stay with tough plants like juniper and cedar, if you are in an appropriate area. Broad leaf evergreens may or may not be easy, you will have to consult your text.
Deciduous material such as maples, hornbeam, hackberry, elm, hawthorn, linden, Malus (apple), Prunus (plum, peach, apricot), and Liquidambar are fairly easy to work with.

And finally

Remember, the strong impulse to have that little tree in a bonsai pot will become a very boring experience if that is your only interest in bonsai. Most people have much more fun with their collections of pre-bonsai and bringing their trees along, watching them grow, planning their future, and finally potting them up as bonsai. These trees, born of love, are much more valuable than mall bonsai.

Integrated Pest Management for Bonsai

by Brent Walston

Introduction

Being a nurseryman means that, at times, I have to deal with pests and diseases. I hate dealing with them, it is the least satisfying part of my job, but it is also a fact of life in the nursery business.

What is IPM?

All the rage these days is IPM, integrated pest management. Instead of going out and periodically blasting everything in sight, IPM teaches that it is better to treat bugs and diseases with levels of increasingly invasive (toxic) techniques. The first level is cultural. Change the environment if possible to deal with the pest or disease. If you continually get powdery mildew, move your plants into the sun and keep the foliage dry at night. Aphids, mites and other sucking insects can be controlled to some degree by regular blasts of water to keep them from getting established. This level is completely non toxic and should be the first thing to do.
If cultural controls fail or are impossible to apply, the second level is to use biological controls. Use predator mites, lady bugs to control aphids, etc. BT is now available for a wide range of pests.
If biological controls fail or are nonexistent for the pest, the last level is to use chemical controls in increasing order of toxicity. The least toxic used first.

Monitoring Pests and Diseases is the Key

I practice IPM in my nursery whenever I can, and the best thing I can say about it is that it increases my awareness of the environment in the nursery. Secondarily, it has saved me lots of money by reducing the amount of pesticides that I must use. Commercial pesticides are very expensive. A single quart of Avid cost $200. A fact that was painfully brought home to me one day as I accidentally tipped over a bucket with about $20 worth.
The premise of IPM is that we never 'get rid of' anything. Pests and diseases are at best controlled, kept at minimum levels where the damage is acceptable. Pests and diseases are a fact of life, and we will always have to deal with them. The question is how will we deal with them.
The key to successful use of IPM is monitoring. Without monitoring the pest levels, one is doomed to blasting full blown infestations with the strongest stuff possible. Monitoring requires one to weekly check representative samples of the crop for pests and diseases. In my nursery this takes between one and two hours, but it is a fun job and a good excuse to get out of real work.
The essential tool for monitoring is a good 5X hand lens. Several insects are too small to see with the naked eye if you are over 40 like me. Two-spotted mites are one of my biggest problems and they are nearly invisible without the lens. I look for speckled discolored leaves, traces of yellow and red, then look at the undersides for traces of debris. A healthy leaf will be completely smooth with the exception of hairs for some species. An infected leaf will be covered with 'dirt', little bits of debris, webbing and eggs. The eggs are translucent spheres just visible even with the lens. Red spider mites are similar but are larger and a little easier to see with the naked eye and leave visible webbing. Red spider mites have a reddish color and are fairly easy to control. Two-spotted mites are translucent with two dark spots on their back and are the devil to control. Both have life cycles of about 5 to 7 days so follow up spraying is always necessary.

Knowing the Enemy and Making Changes

Fungal and other disease problems can also be monitored, with or without magnification. Early detection can save heavy spraying and foliage damage. A really good way to learn about these diseases is to monitor your plants and watch the progress of the pest or disease with the hand lens, you will see all the symptoms. Then, when you need professional help, you can provide the necessary information to get the problem identified and solved. Half the problem is knowing the enemy.
There are fungal diseases for which there is no cure, only cultural control, level one. In the case of some root rot problems cultural changes may be all that is necessary. In the process of instituting such cultural changes, I was recently forced to look at how I water and how wet the plants were staying. As a result I discovered other problems related to over wet conditions and have now acted to correct the problem by hand watering only the plants that are dry. This is the kind of thing that IPM is really good at, it forces one to observe and to act at the lowest level of toxicity, and often this is the very best solution, far better than the chemical warfare to which we have been raised to expect.

Managing a Micro-Eco System

Pesticides are not necessarily a fact of life. I think a really good example is my operation. I have a one acre growing facility where plants are lined up according to species and grown like corn. Since it is a commercial venture and not for public display, efficiency is the key word. Things are much more crowded than they should be, but I have no where else to go. As a result I have to deal with insects and diseases which thrive on this arrangement. It is a never ending battle of fungal diseases and bugs, especially mites and aphids.
On the other hand I have a retail store where things are spaced evenly and attractive, a good diversity of plants and much hand watering which has a good washing action. I stock plants at my store with plants from the growing grounds. Now I never try to intentionally infest my store with pests so I am always looking for clean stock to bring in, but in over seven years of operation I have never sprayed for mites in my store. It amazes me, but I attribute it to good cultural practice, probably some natural predators in the area, and the hand watering which tends to limit mite infestations.
This is not to say mites have never gotten in there. I find them occasionally, but they never reach levels that endanger or disfigure my plants. I find them on their favorite targets but they never seem to spread. I monitor them all the time to make sure the damage is nonexistent or minimal. There is a natural balance going on in the store that is obviously not going on in my growing grounds. The natural balance has never been upset and I don't intend to upset it by spraying unless I really have to. I think that once this symmetry of natural control and balance is upset it is extremely hard to reacquire.
This is an incredibly complex topic and I think there is room for systemic insecticides for aphids without upsetting the balance, but I also believe that natural controls for even this pest if carefully managed would obviate a need for the chemicals.
The problem is that spraying for pests will usually upset any natural balance of predator organisms which may be present. Predators are not always other insects or mites. There are beneficial fungi and bacteria as well, possibly even beneficial viruses as yet undiscovered. There are even minerals in water that can favor or diminish the pests or the predator (beneficial) organisms. Very little is known about any of this but we see it all the time. My advice is: If it ain't broke, don't fix it. If insects, mites and fungal diseases are not a serious problem leave them alone or use the least toxic method possible first. If your trees are in danger then the balance probably has already been upset and using more toxic methods will probably do little more damage. This is the essence of IPM.

And finally

I think the key word here is balance. We, as humans, seem destined to unbalance the entire earth. Can we save our selves and the environment and our little bonsai plants by becoming aware?

Intact Rootball Vs. Rootbound

by Brent Walston

edited by Robert Potts

Introduction

A continued discussion of healthy roots by Brent Walston, taken from postings on Bonsaisite Forums.
RP

What's an intact rootball?

An intact rootball is when you can knock the nursery can or pot off the root ball and it won't fall apart. This is sort like the advice of bending the branch to the point where it is just about to break. How in the world do you know without doing it? There are several tricks. You can wiggle the stem. If it stem moves in the pot, don't try unpotting it. If the stem seems pretty solid, try the next test. Try to pick the plant up by the stem. If the surface starts to give before you can pick it up, it is too soon. If you can pick the plant and pot up by the stem, do the next test. With a surface just under to pot to catch it, knock the pot off the roots. Don't pull it off. The proper procedure is to hold the stem in one hand and give the rim of the pot a sharp rap with the palm of your other hand. If the pot drops off cleanly and the rootball doesn't fall apart, you can pull it and inspect it. If the pot falls to the surface and the root ball collapses back into the pot, it's too soon. That's why you want something just under the bottom of the pot.

Why inspect the rootball?

People don't inspect rootballs nearly enough. Hardly ever do I read a post asking for help where the pot has been knocked of and the roots inspected, even though this is the most revealing test you can perform. I do it all the time for healthy and sick plants just to see what is going on. A healthy growing plant will have a nice intact rootball with lots of lovely white growing root tips.

Rootbound?

At what point do plants stop growing in a pot? It's a bit involved, but the simple answer is that new growth stops or slows when they become rootbound. So what's rootbound? Rootbound is when there is no effective space for new roots to occupy. Roots effectively occupy the entire volume of space between the soil particles. One of the first symptoms of being rootbound is, in fact, that plant growth slows despite favorable environmental conditions (light, water, fertilizer, etc). The second symptom is that rootbound plants begin having difficulty taking up fertilizer. This is undoubtedly related to the inability to form new root tissue. You see this as a chlorosis despite the fact that they have been properly fertilized.
People often confuse leaves with new growth. New growth is the process of continually opening the terminal bud of a stem (shoot formation). Plants can be, and frequently are, alive and relatively healthy with absolutely no new growth. This happens when plants are severely rootbound, there is a lack of fertilizer, or after a trauma such as barerooting. The existing buds will open, leaves will form, but no shoots will develop. This condition will persist until conditions change. I have seen many plants survive year after year without shoot growth. New growth each year consists of a succession of opening terminal and axillary buds in the spring without any shoots to form an internode. If you look closely at the stems there are just a pile of leaf bundle scars piled up on one another. Talk about close internodes!
Rootbound plants need to be rootpruned and shifted at the nearest appropriate opportunity. This usually means winter, because unlike shifting an intact rootball, rootbound plants must be rootpruned to initiate proper root growth.
It is difficult to tell when a plant is rootbound just by observing the roots. I think it is better to determine 'rootbound' by both the symptoms of growth (or lack thereof) and the physical density of the roots. For our purposes (bonsai), trees should be rootpruned and repotted long before they reach rootbound conditions. This doesn't happen overnight. There is a long gradual procession of slowing growth over time, usually several years before all new growth stops. It is clearly evident what is happening if you stop to look.

Root growth patterns are species dependent

Some species quickly occupy the soil mass uniformly (Buxus). And yes, there are species that love to occupy the bottom of the pot with roots, but not the top,Cedrus and Quercus come to mind. But given enough time, both of these genera manage to occupy the entire soil mass, albeit over many years. While doing this, shoot growth is present, but obviously slowed. Growth of this kind presents a problem when root pruning and repotting because you often don't really know where the root crown is. It is very easy to buy a rootbound nursery plant, slice off the bottom portion of the roots with a saw or axe, and then find out you just cut off the bottom of the trunk. You have to proceed slowly and carefully when root pruning rootbound trees. It is difficult and arduous.

And finally

In this, as well as most of the other articles at this website, I have tried to point out that container growing is a system. Rarely can you change one condition without changing others or changing the growth dynamics. At first it may seem like a daunting task to understand the interrelationships, but it is a necessary to learn these processes to be able to successfully manipulate plant growth.

Using Principles of Growth to Manipulate Plants for Bonsai

by Brent Walston

Introduction

This is an article that will show you how to apply basic concepts of plant growth to bonsai training techniques.
Growing plants for bonsai means developing a nursery plant to the point of final styling and placing it in a pot. These plants have a variety of names, i.e. pre- trained or pre-bonsai, etc. The idea is to grow a plant specifically for bonsai rather than landscape. Since our ends are very much different than landscapers the techniques are also very much different. Some plants, such as pines need special attention from the very beginning to become good bonsai, others such as most deciduous trees are much more forgiving and may still be used after achieving some size, but without any previous bonsai training.
The approach that I would like to take is that of explaining and applying plant growth principles so that you may apply these principles and concepts to your particular situation. Once understood, these principles are a very powerful tool for manipulating plant growth. And bonsai is probably the epitome of plant growth manipulation.

Principle 1:

Leaves (needles) increase the size of the woody parts of the plant and the size of the roots.

Well, that seems obvious. But most of us fail to use this concept to its maximum advantage. If you want a really large trunk, don't prune your plant. The removal of leaves will only slow it down. This is of course over- simplified but nonetheless true. If you root prune a plant, leave as many leaves as the roots can support to generate new roots as quickly as possible. If you do this while a deciduous plant has its leaves, you must reduce the foliage comparably to prevent overtaxing the root's ability to supply water. It is imperative to keep the plant cool while new roots are being regenerated.
Leaving the entire stem of deciduous plants works particularly well for bare-root plants or severely root-pruned dormant deciduous plants. The remaining roots will only stimulate as many buds as they can support, so do not top prune the plant. (See the article "Root Pruning Bare Root Seedlings)

Principle 2:

Leaves manufacture plant food, roots store plant food.

OK, obvious again, but what are the ramifications? Top pruning a plant at the end of the season (fall or winter) leaves all of the food intact to stimulate new growth in the spring. A full complement of food with no where to go will stimulate new buds and the new growth will be explosive and coarse, some deciduous plants may send out an eight foot sprout one inch thick in a single season (or more!). Severely top pruning a plant just after it leafs out in the spring uses up most of the stored food because the roots must send out a second burst of food to stimulate even more buds. This depletion will cause very weak new growth and will slow the plant down.
Not pruning a plant in winter or spring leaves the maximum number of buds to be stimulated into flowers and leaves and twigs, this taxes the roots to the fullest and will produce the smallest leaves, and the closest internodes (spaces between the leaves) on the new stems. Confining roots, as in a bonsai pot, limits their ability to store food, which in turn will diminish the leaves and internodes even further. This is the basic mechanism for dwarfing a plant in bonsai.

Principle 3:

Small twiggy growth will always remain small and twiggy.

This principle is not so obvious and is in fact frequently overlooked by bonsai folk. What I mean is that, when a small twiggy branch appears as the result of restricted growing conditions it will always keep this character, even if the plant is rejuvenated by repotting or planting in the earth. New growth will be coarse and vigorous with long internodes and large leaves, but the twiggy branch will be unaffected. Thus you can grow a bunch of nice small branches low on the tree, plant it in the ground and grow a sacrifice branch or leader to increase trunk size enormously, come back and cut off the sacrifice branch and have a big trunked tree with nice small branches. However this will only work if you do not allow buds from the small branches to break into a water sprout or coarse growth. The branch will remain twiggy but its diameter will increase until it is unusable.

And finally

These few principles may sound simplistic, but they are the entire basis for manipulating plant growth in bonsai. You will need to think about them carefully to be able to apply them effectively. To see how their application can work for leaf and stem reduction see the article "How to Reduce the Size of Leaves".

Aging of Container Soils

by Brent Walston

Introduction

There is a changing dynamic relationship between an individual plant and its soil in a container. We realize that plants grow and change, but we don't consider that soils 'age' as well. In container growing, it is important to match the life expectancy of the soil to the frequency of repotting. This insures that your bonsai and other container plants won't be forced to struggle in a 'collapsed' soil mix. As soils age, they tend to break down, reducing the particle size and retaining more water. This process can actually match the growth rate and water needs of the plant, if carefully balanced.

In the Beginning...

Newly repotted plants don't take up as much water (in general) as leafy established plants. This is because the root system is compromised when repotting is accompanied by root pruning and combing out of old soil. We take this into account by reducing transpiration by reducing the foliage, or repotting while the plant is dormant.
In establishing a new root network, aeration and fertility appear to be the prime factors, not water holding capacity. Of course there must be enough capacity to allow for transpiration, but the rate of transpiration is much less at the time of transplant (and shortly afterward) than after root establishment and consequent new growth.

But Then...

As the roots grow and new shoots and foliage develop, transpiration increases. This can be dealt with by pruning to reduce transpiration, increasing the watering, reducing sunlight, etc. But one of the really nice things about having an organic component in the soil is that it begins to break down about the time the plant is demanding more water. This effectively increases the water holding capacity. A well designed soil and proper plant maintenance will help keep the moisture content in balance.
Once soil is thoroughly root colonized it is not subject to collapse for most species unless the plant is subjected to poor treatment such as massive overwatering, not enough direct light, etc. The root network will tend to keep the soil aerated by creating a woody framework. In fact, fine particles will often be washed out of a healthy root network.

Peat Moss and Nursery Mixes

Peat moss, when used in reasonable quantities of less than ten percent, does not add sufficient small particle volume to affect either drainage or aeration. That is what I really like about it. It is so efficient at retaining water without using up space, that it makes an ideal amendment for this purpose. Its lightweight fibrous nature also keeps it in position in the soil mix, rather than washing it quickly to the bottom. The old "UC" mix developed by the University of CA (Davis, I believe) was 50% peat moss and 50% fine sand. This of course was a nursery container mix, not for bonsai. It was used for years until the cost of peat moss forced them to change it.

Soil 'Shelf Life'

What you must understand is that the UC mix and all the other nursery container mixes are designed for quick growth and short 'shelf life'. Ideally, typical nursery plants don't stay in the same pot for more than one or two years (five gallon and under sizes). Any longer than that usually results in soil collapse or root bound conditions. Bonsai mixes must last longer, and they must be more flexible and stable to account for pruning and training. Except for training pots, we don't allow full flat out growth. This means that we have to pay a lot closer attention to soil characteristics than general nurseries do.
I try to make my soil mixes last as long as possible, even those in training pots. I use fresh bark and stable inorganic amendments (lava rock and perlite). This soil will last many years before the bark completely breaks down. Usually by that time the roots are in need of pruning and attention anyhow. That is how a soil should be designed, to last as long as the plant needs to stay potted.

All Inorganic?

Using only stable inorganic components such as lava rock or pumice will create a soil that will last longer than it really needs to last. Using only unstable inorganic amendments such as clay baked to much less than vitrification, akadama, etc. creates a soil that may not last as long as it needs to for some plants, although it is usually fine for two or three years. I have used pure fir bark, and it worked beautifully for about four years, but now I am repotting those plants because it is now quickly breaking down. A combination of stable inorganic and fresh organic amendment (fir bark), works fine for me. I get the right breakdown curve for repotting practices, higher CEC (cation exchange capacity), good aeration and drainage.

And finally

I think, and this is just my opinion, that you will simply get a different set of problems no matter what you use for soil. If you use purely inorganic components, you will probably have to use organic fertilizers and their attendant problems such as removing the surface residue, smell, insects, etc. If you use more than an optimum amount of organic components then you will get problems related to water and aeration, quick breakdown and collapse which you will have to overcome with closer attention to watering practices. There is no 'best' soil, there are only soils that work well in a set of environmental conditions that include the species of plant, how it is manipulated, who is doing the manipulations, watering, the climate, fertilizer type and practice, light/shade. All these things are interrelated.

Soils for Containers and Bonsai

by Brent Walston

Introduction

Soils for container growing, and that includes bonsai, are very different from soils used in gardens and field growing. In the following article I will discuss the necessary parameters for container soils and how to use them to develop good container mixes.

Soil Basics

The study of soils is centered on the size and composition of the particles. Particle size varies directly with air retention, and inversely with water retention. This means that, as the particle size decreases, so does the amount of air retained at the saturation point. It also means that, as the particle size decreases, the amount of water retained increases
We all know this intuitively and actually work with this principle all the time in the garden. Clay soils retain more water and less air than sandy soils. Interestingly, we often use the same cure for both extremes, the introduction of organic matter. Organic matter is very good at water retention. Soil amendments, such as peat moss can hold many times their weight in water. It is obvious that this would help a sandy soil, but how does it help a clay soil?
As long as the organic matter particle size is not too small, and the amendment is thoroughly incorporated, clay soils are improved by 'aggregation'. That is, the inorganic and the organic soil particles tend to clump together to form larger aggregate particles that will trap air between them as well as water within them. This improves the aeration, or air retention of the soil. Stated differently, it improves the drainage.
Clay has a tremendous ability to retain nutrients, organic amendments have a lesser ability, and inorganic larger particles such as sand have very little. Container soils which contain little or no clay or native soil, must be fertilized regularly to overcome this deficiency. Also, soilless mixes (those that contain no native earth), will usually be deficient in trace elements, and these will have to be added in some manner.

Bonsai is a Nursery Container Practice

Bonsai is container gardening, and in that sense, is little different than general nursery work in the mechanics of soils and drainage. Soils for containers should drain 2 to 3 times faster than native soils. The earth acts like a huge suction pump and can literally pull water from heavy soils. But this same garden soil in a container is usually instant death for your plants. Because of the impermeable walls and bottom of the pot, this same soil will not drain properly. Container mixes should drain so fast that you can stand there and watch the water flow through.
Most nursery mixes these days are 'Soilless', that is, they contain no native soil, except possibly washed sand. They may contain compost. They are usually composed of three elements:

• Inorganic structural element: lava rock, perlite, sand, baked clay, decomposed granite, pumice, etc
• Organic structural element which can hold some water and nutrients: fir bark, pine bark, nitrolized redwood chips, etc.
• A water holding element (optional): compost, peat moss, or vermiculite

Water Retention and Drainage

Soils must drain quickly, but still retain a reservoir of water, 25% percent by volume is considered optimal. The air space after initial drainage (the saturation point) should also be about 25%. It is hard to beat peat moss for water retention without adversely affecting drainage. Peat moss is also effective at nutrient retention. Vermiculite after it begins to break down to its basic clay constituent is also very good water and nutrient retention, but must be used conservatively, because it is after all, clay.

Pathogens

Anytime you use compost (unless it has been pasteurized, or thoroughly composted) or native soil you run the risk of introducing pathogens, insects and other pests. If you are a believer in the necessity of these elements, pasteurize them them by putting them in an oven bag with enough water to moisten, and heat to 140F to 160F degrees (internally) for about half an hour.

Mixes Vary with Container Size and Species

I use several mixes for my nursery plants (including bonsai) according to the species of plant and the size of the container and also the cost of the constituents. For my liner (small starter) pots to about seven gallon size pots, I use extremely fast draining mixes because nothing is surer death to a seedling or rooted cutting than a dense soil. You should be able to easily 'see' big air spaces.
The formula is very simple: eight parts screened fir bark 1/4 to 3/8 inch size, eight parts screened perlite, one part peat moss, one half part vermiculite (optional). I also incorporate Osmocote time release fertilizer. Mixing in a cement mixer makes it very easy and pretty cheap. This is an excellent mix for bonsai, except for aesthetic reasons you may wish to replace the perlite with other inorganic structural elements such as decomposed granite, turface, pumice, etc.
This mix will dry out very quickly, but it will get you maximum root growth in the shortest amount of time.
The above mix works well up to seven to ten gallon size. The larger the container the denser the soil mix is the rule in nursery practice, until you are planting in the earth where the densest mix occurs. For ten to fifteen gallon size and larger, I substitute unscreened fir bark (3/8 inch minus it is called) for screened bark, reduce or eliminate the the peat moss and replace the perlite with 3/8 lava rock. This makes a denser, less expensive mixture that will not dry out as quickly, but since bark does not quickly decompose, it will not quickly collapse (more on this later).
This mix works especially well for slower growing species that need excessive aeration. Faster growing species will do better with a denser mix of more traditional nursery mix of nitrolized wood fiber, sand and compost. It is about 80% redwood shavings.
Most beginner gardeners and bonsai growers usually use a mix that is too dense, thinking that what grows them best in the earth ought to work just as well in a container. This is not the case.

Root Colonization and Soil Collapse

This next point, which I have discovered after years of throwing out dead nursery plants, is not obvious and will not be found in most books.

In a container there is a race going on between the growth of the roots and the decomposition of the soil.

If the organic soil elements compost or decompose before the roots can completely colonize the pot, the soil collapses and loses its drainage and air spaces, and the root growth stops. If the roots fill the container first, the soil will not collapse because the roots will form a structure that will support the plant and the soil, and drainage will be maintained.
I have even seen rootballs nearly devoid of soil because of erosion, but uncollapsed because of the root network. This is not as important in finished bonsai because we tend to use premium soils with few organic elements that can collapse, but it can happen if you use too high a proportion of compost or wood fiber, other than bark (which decomposes slowly). This is a very important point for growing out plants for bonsai, where we use larger containers and less expensive and denser soils.

In any soil mix, time, watering, weathering, chemical and biological decomposition tend to produce smaller particle size , loss of air space and drainage.

I call this process 'Soil Collapse'. For the organic elements of the soil, this can occur very quickly. For the inorganic elements, it is usually a slower process, but can be rapid for some volcanic soil amendments and decomposed granite. It is important to match the 'soil life' with the rate of root growth to make sure that root colonization occurs before soil collapse. The root colonization rate varies with the species, fertilizer, water, sunlight, and pruning practices. These are all interdependent forces. That is, plants will grow faster under optimum light, fertilizer and full foliage conditions, thereby decreasing the time needed for the roots to colonize the container. Plants grown in more shade than they like, suffer greatly from this effect because top and root growth slows and soils tend to stay wetter increasing the rate of organic decomposition.
In the nursery business, soil is a large part of the bottom line and premium materials are not affordable for all plants. For fast growing annuals, perennials and woody trees and shrubs, soils that contain a high percentage of wood fiber, as much as eighty to ninety percent, are perfectly acceptable. Slower growing plants require more sand, bark, perlite, etc. that will break down more slowly.
After years of trying to make my plants adapt to my soil mixes, I have realized that it is much better to adapt my soil mix to my plants. I grow less and less landscape material and more bonsai related material so my mixes are now all bark and perlite (or pumice) based. I find that the collapse theory works quite well in predicting what mixes will succeed with what plants.
For a more indepth treatment of this subject see the article Aging of Container Soils.

Premium Materials

In bonsai, there is so little soil involved that cost is rarely a factor. Premium soil mix components are a small part of the bottom line. However, some components work so well that we use them anyhow, such as peat moss. Peat moss is not a necessary component but its excellent water retention makes it a valuable component in very hot areas where watering only once a day is desireable. It is often the decomposed peat that one finds in the bottom of the pot.
There is always a tradeoff in soil mix components. I prefer porous volcanic materials such lava rock, pumice, and perlite (a sort of manmade volcanic rock) because they are light weight, hold water and air and are readily available. But they do break down, and after several years one finds evidence of this in the bottom of the pot. I also use DG, decomposed granite. You can screen it to get any particle size you want to get excellent drainage, but some grades break down rapidly. I have been very lucky to obtain a grade that has probably been mined from a source near water, so the weathering has been minimal and it is very stable. On the minus side, it is heavy and has no water retention.

And finally

After fifteen years of this, I am still playing with soil mix formulas and this seems to be true of most nurseryman, so there will probably never be an end to this thread.
For more soil mysteries explained, see the companion article Why the Earth Is Not Like a Pot.

How to Germinate Seed

by Brent Walston

Introduction

For years I grew most of my plants from cuttings and bought my seedlings because I had a feeling that seeds of woody plants were another five to ten year learning project just like cuttings. I was right too. I owe a great debt of gratitude to Norman Deno for just about everything I know about seeds. His book on seeds is just as important as Dirr and Heuser on cuttings. If you have one book on seed it should be this one: Seed Germination Theory and Practice, Norman C. Deno. You have to order from him and I understand there is an update that I do not have yet. The address I have is 139 Lenor Dr., State College PA 16801, USA. Buy the book, we should support people like Deno, who work outside the traditional establishment, but who revolutionize the industry on the sheer strength of their ideas.
Deno at long last establishes a system for understanding the germination of seeds. His theory is that fruit and seeds contain chemicals in their pulp, seed coat or embryo that inhibit germination. Deno is a physical chemist not a botanist so he understands this stuff. These chemicals are barriers to germination and must be removed, often in order for seed to germinate. Forget terms like stratification, they are now archaic. It originally referred to the practice of layering seed in beds that were kept cold, to layer or to stratify. I prefer to use the terms that Deno uses, because they more accurately describe what is going on. These terms are 'germination inhibitors' for the chemicals that must be removed, and 'pre-treatment' for the processes involved. I think it is the least that we can do to honor the man's work.
The chemical reactions that take place to break down some of the germination inhibitors are quite unusual in that they require moisture and temperature within a specific range, not colder or hotter. As a physical chemist Deno has identified this type of reaction and explains how it can happen, although we needn't be concerned about it here. Another inhibitor is broken down at warm temperature, another by a fungus, one by lack of light, and one in the presence of light, although the light triggered ones seem to work in conjunction with the fungus. One type of inhibitor is present in most fruit pulp and must be physically removed. In addition there are physical barriers that must be broken down such as impermeable seed coats. Deno lists all of these in what he calls the nine principles. I am not going to give you all nine, but I will summarize the most common problems in seed germination.

Inhibitors Broken Down by Moisture and Temperature control

First you must understand that seed from different species and even different CULTIVARS is different and may exhibit different inhibitors. Deno is compiling an encyclopedia to identify the the inhibitors for each species he can. Unfortunately for us he is more interested in rock gardening and alpines than woody plants, but there are many references to them and even more in the update, I understand. But by understanding the principles it is quite an easy matter to identify the inhibitors yourself with a simple series of experiments with seeds in moist paper towels.
Some inhibitors are broken down under moist conditions at 70 degrees (Fahrenheit) and others at 40 degrees. Seeds may, and often do contain more than one inhibitor. There is a curve of germination for each species that describes the rate of germination over time, but for our purposes neither of these cycles takes longer than ninety days for the vast majority of plants. If the cycle is shorter than this you can easily determine it by checking the paper towels each week to see if the seed has started to sprout.
Most temperate woody seeds will contain an inhibitor that will require a forty degree cycle followed by a seventy degree cycle. This only makes sense, since it is natures way of protecting seed from germinating while it is still too cold. Sometimes the inhibitors must be broken down in order, first forty then seventy, or vice versa. The seed will not germinate until this happens. Some species require multiple cycles. That is, there may be more than one forty or seventy degree inhibitor present, and when this happens they are broken down one at a time. Thus you must alternate three months of forty followed by three months of seventy until germination occurs. I have written that Acer japonicum requires just such a multiple cycle.
The beauty of using moist paper towels and plastic bags to pretreat seed is that you can do all this work without trying to stick a flat of dirt in the refrigerator. When the seed finally germinates, remove it from the bag and sow, one at a time if necessary, and this is often the case. I prefer to wait until the radicle just emerges and then plant it in a plug tray or cell. This eliminates much of the waste involved in planting seed. You know that the seed you planted is going to come up because it has already germinated! This is particularly nice for rare and valuable seed when you only have a few.

Fungal and Light Reactions

Buy the book. But I will tell you that the majority of seed that you and I are interested in do not have these types of inhibitors.

Inhibitors present in Fruit Pulp

Deno points out that these inhibitors are much more common than people believe. We don't see it much because it is common practice to wash seed anyhow or to allow the pulp to disintegrate over the winter. But if you collect fruit to acquire seed it is imperative to follow this procedure to remove any possible inhibitors. Wash the seed to remove all traces of pulp. You can do this mechanically or allow it to ferment so that it falls away. Once relatively clean, wash the seed every day for seven days to remove all traces of fruit and the inhibitor. Most of these chemicals are water soluble, but a very few are oil based and the addition of a very small amount of detergent will dissolve these.
This has worked very well for me with Dogwood, (Cornus), Ginkgo, and Prunus mume.

Impermeable Seed Coats

There are a few woody species that have hard seed coats that will not allow water to pass to begin the pre-treatment process, or the embryo to expand. If seed is collected fresh and moist you have already solved the moisture problem. You can temperature pretreat and then nick the seed coat afterward to allow the kernel to break out.

How to Experiment

Take SOAKED seed and place it in paper towels and place in thin plastic bags such as baggies and fold over the top. It has not been demonstrated, but it is entirely possible that oxygen is necessary for the reaction to proceed. Keep it at seventy degrees for ten days to two weeks if you don't know whether or not a forty degree inhibitor is present. In my experience, if no 40 inhibitor is present and the seed is fresh, it will begin to germinate right away.
If you get nothing at the end of two weeks put it in the fridge for three months, checking it each week for signs of germination. Often fresh woody seed will begin germinating after one month. At the end of three months and no germination takes place, then a seventy degree inhibitor is most likely present. Keep the seed at about 70. For most woody seed the inhibitor is broken down quickly and it will begin to sprout in a week or two. If not, hold it at 70 for three months. If nothing happens, a second 40 degree inhibitor is present (assuming of course that the seed is viable). Back to the fridge, repeat the cycles until germination occurs, you have a fit, or the seed rots.
You can of course, run multiple experiments if you have no information at all on your seed. One bag in fridge, one at 70, etc.
A few notes on care. The seed must stay moist INTERNALLY throughout this process. Deno doesn't talk about this much, but my experience with woody seed is that it can stay a lot drier on the outside than most people would believe. Keeping it this dry eliminates a lot of the fungal problems involved with long storage times. This is why I am so particular about getting fresh seed that has not been dried, it already has internal moisture and if an impermeable seed coat is present it won't make any difference.
Some tips on determining the proper moisture: Know the difference between moist and wet. If a film of moisture is on the seed or the plastic bag it is wet not moist. The paper towel should feel almost dry. If it starts to get stiff during the process, it is dry, and a very few drops of water should be added or a single spritz from a spray bottle.
For seed that does not take long to pretreat such as Cedrus I don't even use paper towels or other media, I soak the seed, dry it in the sun for about fifteen minutes until the outer husk feels dry to the touch and put it in a baggie and into the fridge. The seed is very fleshy and retains adequate water for the month that it must stay in there. Cedrus is VERY sensitive to excess water and will rot in an instant (see my Cedrus article for more info).
If your seed does get very moldy but has not yet cracked the seed coat you can wash it with a ten percent bleach solution. Let dry, then return to storage in fresh bag and towels. Deno points out that sound seed has natural antibodies for most fungi, and this is true. But keeping seed too wet is just too risky. Once you get a pathogen it seems like you have it for life and precautions are in order.

Fresh Seed

I can't overemphasize how important it is to get fresh or properly stored seed. Deno has get fun pointing out that a lot of seed arrives fresh from the supplier and DOA, dead on arrival, simply because it has been dried. The most notorious example is Acer rubrum. It cannot be dried whatsoever and must be collected fresh and moist from the trees in the spring and sown immediately. It germinates in about ten days without any pre-treatment.
I have spent hundreds of dollars on Acer palmatum seed without a single seed germinating until I finally got smart and collected my own in Oct and Nov. The best seed will still have some color to the wings and the fleshy part will still be a little moist. If the seed is collected at this stage and refrigerated without further drying it will keep for some time, but most companies don't bother doing this. Other problem seed like this is Carpinus, and Fagus. I use to think that over drying the seed put it some state of deep dormancy, but now based on Deno's work, I think it either kills, as in the case of Acer rubrum, or allows the seed and seed coat to dry and harden and become semi-impermeable so that you cannot get water to the embryo no matter how long you soak.

And finally

I have probably forgotten about a half dozen things, but this should get you started germinating your own seed. Seed from bonsai is a very long term process, five years for even very small bonsai, so don't let this be your only strategy. But, it can be very rewarding as part of your overall plan of plant material acquisition.

Why the Earth Is Not Like a Pot

by Brent Walston

Introduction

In bonsai we work very hard to create and maintain highly aerated soils, yet when we plant in the earth, the soil is incredibly dense. How can this be? The answer to this and other soil mysteries are below.

A Pot Isn't Like the Earth

The major difference between a pot and the earth is that a pot has impermeable sides and bottom. This reduces air exchange in two ways. First is the obvious, air cannot pass through the plastic, thus we have a contained volume of soil encased 75% with air tight plastic (or high fired ceramic (low fire ceramic will breathe). This is why I design my soil mixes and other environmental factors to 'dry out' the pot once a day during the growing season. Each time the plant is thoroughly watered, it pulls a new charge of air in behind it as the water drains.
Secondly, we have to visit our old pot size argument again. When a downward moving table of water reaches an impermeable layer (in this case the plastic pot bottom) it will not drain until the layer just above the impermeable layer (pot bottom) is saturated. Once this lower layer of soil is saturated, excess water will drain out, but a column of saturated soil will remain since the moving table of water has stopped at the impermeable layer. This means that the soil in the bottom of the potremains saturated at this lowest level after watering, and stays saturated until something happens to change that condition. That 'something' is primarily absorption from the roots in the bottom of the pot, the secondary factor is (or should be) evaporation. You will probably want to read this paragraph again, and perhaps a third time, it is not obvious.

Overpotting

Most of the water in the pot is removed from the pot by absorption by the roots and not by evaporation. If you overpot, it will take a long time for roots to colonize the bottom of the container and consequently it will take much longer for the saturated layer to become fully aerated (the only factor at work is evaporation). Overpotting will generally lead to too wet conditions and eventually root rot.
This phenomenon is also true of planting in the earth, but only when stratification of the soil is present to cause an impermeable layer, such as when you are planting on a layer of clay or hardpan, or you create a boundary between two dissimilar soil types. Otherwise, there is no impermeable layer and the water continues its downward movement into the earth, creating no saturated layers. This is why (along with the absence of impermeable walls) that we can, and do use denser soils when planting in the earth: no saturated layers are formed (until the water table is reached).

Creating Aerated Earth Soils

I have seen saturated layers created in the earth kill plants just as heavy soils in pots do. I was once asked to examine a dying Rhododendron which was planted in a straight fir bark bed. I knew that the area had heavy clay native soils. I dug up the Rhododendron, and sure enough, about a foot down was a layer of solid clay and the fir bark layer just above it was saturated with water.
Other loose experiments I have been conducting involve using highly aerated soils in growing beds. From the above argument you can see that we can use heavier soils in beds, but will using the same highly aerated potting soils that we use for containers improve growth rates? I think the answer is yes, I have had Chinese elms grow about twice as fast in a highly aerated bed than in a creek side silt bed loaded with natural nutrients from yearly flooding, but comprised of mostly fine silt.
The problem with the highly aerated beds is that they will require a lot more water and nutrients than a good garden soil, for example. And again, you must be careful not to create a boundary between a dense soil and the amendments at the bottom of the bed or you will create a saturated layer at the bottom. You can usually avoid boundaries by loosening the native soil at the bottom of the bed and mixing a smaller percentage of the amendment in with the native soil. This will give you a transition zone rather than a sharp boundary.

What About that Saturated Column Thing?

Ok, just how high a column of saturated soil do you get in a container? The height of the column of water retained in the soil by an impermeable layer is related to size of the particles. Sound familiar? The denser the soil, the higher the column will be and the more water will be retained. Large particle, highly aerated soils will not support a large saturated volume. This is what we mean by 'well drained'. You can test this for yourself. Take a regular sponge, soak it with water. Rest it in your hand horizontally until the water stops running out. Then tilt the spronge upright. You are now increasing the saturated column. The sponge density won't support a column that high and water will drain out.
This experiment also shows that pot shape is related to water retention. A broad shallow pot will retain more water than a tall narrow pot of equal volume. Although it is counterintuitive, a shallow pot will retain more water and 'dry out' more slowly than a tall narrow one (of equal volume). Another reason we use such coarse soils for bonsai, and also why bonsai can survive in such tiny containers on very hot days.

And finally

Soil physics may not be obvious, but knowing what goes on under the surface is bound to lead you to more successful bonsai.

The 'Rules' of Bonsai

by Brent Walston

Introduction

As in all arts, bonsai usually conforms to a set of conventions, guidelines, or 'rules'. Rules is probably the worst word of the three to describe what most artists do to create bonsai, but it is the word that most people use. These rules are not cast in stone and are frequently broken as the situation demands, but they are excellent guidelines for the creation of beautiful bonsai, and are invaluable to persons learning bonsai. They simplify what otherwise would be a bewildering set of decisions.
These rules mostly come from the Japanese culture of bonsai over the last few centuries. They are an analysis of what 'works', and what 'doesn't work' in the creation of bonsai. Almost anyone can create a decent looking bonsai by following these rules, whether or not one has any native talent. That is the beauty of this distillation. Of course, very good bonsai will still depend upon talent, experience, inspiration, and serendipity, as well as a general conformity to the rules of bonsai.

Trunk and Nebari Rules:

1. Height should be six times the caliper of the trunk.
2. Trunk should lean slightly toward the viewer.
3. Trunk should flare at base to visually anchor the plant.
4. Roots should radiate from the flare.
5. No eye-poking roots (directly at viewer).
6. Apex should lean toward viewer.
7. Trunk should taper as it ascends. No reverse taper.
8. Grafts should match understock and scion so that they are unobtrusive, or be placed low enough to disappear into the nebari.
9. Curves in trunk should not result in 'pigeon breast' (roundness toward viewer).
10. Apex should finish in the direction set by the base. 'Flow' should be maintained.
11. Trunk line should not move 'back on itself'. This is one of my rules and difficult to explain. It relates to the flow of the tree. A trunk line that moves back on itself creates a 'C' curve.
12. For formal and informal upright, the apex should be over the base.
13. In informal uprights, too many 'S' curves will be tiresome.
14. As a tree ascends the curves should be closer together (related to branch placement).
15. A tree should have only one apex.
16. Twin tree trunks should divide at the base, not higher up.

Branches:

1. No crossing branches, or branches that cross the trunk.
2. No eye-poking branches (pointed directly at viewer).
3. First branch should be placed approximately one third the height of the tree.
4. Succeeding branches placed at one third the remaining distance to the top of the tree.
5. Branches go on the outside of the curves (No belly branches).
6. Branch caliper should be in proportion to the trunk. Branches that are thicker than one third the trunk caliper will be too thick.
7. First branch should be left (or right), second branch right (or left), third branch should be back branch.
8. Branches should visually alternate, no parallel branches.
9. Branches should diminish in size and caliper as they ascend.
10. There should be space between the branches to 'Let the birds fly through'.
11. First and second branches (Left and Right branches) should be placed forward of the mid line to 'invite' the viewer.
12. First, second, and third branches are approximate 120 degrees apart, with the back branch not directly behind the tree.
13. Only one branch per trunk position, no 'wheel and spoke' or whorled branches, or bar branches (branches directly opposite each other).
14. Branches should create an outline of a scalene triangle with the apex representing God, the middle corner man and the lower corner earth.
15. Secondary branches should alternate left and right and follow the rules of main branch placement, except there should be no secondary branches moving up or down. This creates the foliage pad.
16. To create the illusion of an old tree, wire the branches down. Young trees have ascending branches. The branches near and in the apex can be horizontal or ascend since this is the young part of the tree.
17. Branches for cascades generally follow the rules for uprights, except that the trunk moves down.
18. In twin trees, there should not be branches between the trees which would cross the trunks. The outside branches of both trees creates the triangle of foliage.
19. A jin should not be hidden in foliage.

Pots:

1. The tree should be placed behind the mid line of the pot, and to the left or right of the center line.
2. The depth of the pot should be the caliper of the trunk, except for cascades.
3. Colored glazed pots should be used for flowering and fruiting trees and the colors should complement the flower color.
4. The width of the pot should two thirds the height of the tree. For very short trees, the width should be two thirds the spread of the tree.
5. Style of the pot should match the tree. Uprights without much movement should be in rectangular pots, informal uprights with a lot of trunk movement should be in oval or round pots. Massive trees should be in deep rectangular pots.

Culture:

1. Soils should be uniform, not layered. (New rule, you will still find controversy).
2. Fertilize full strength. (New rule, there will be controversy).
3. Water from above, not by submerging the bonsai, this will prevent the buildup of salts.
4. Increase humidity by using a tray of pebbles and water or by keeping the area under the bench wet, not by misting. (This is my rule, there will be controversy. Misting increases the salt buildup on the leaves, and does practically nothing to raise humidity.)
5. Remove most of the 'fines' from any soil mix, using only coarse particles.
6. Water when the plants need to be watered, not by a fixed schedule.
7. Keep temperate climate plants outside. Only tropical and subtropical plants (for the most part) are suitable for indoor bonsai. Temperate climate plants must be given an appropriate period of cold dormancy if they are to be kept indoors.

And finally

John Naka's book Bonsai Techniques I, 1973, Bonsai Institute of California, is by far the best treatise on the 'rules' of bonsai that I have found. Anyone can create convincing bonsai by following these conventions. Once they are mastered, you can begin to create without thinking about 'rules'.
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The Limits of Fertilization

by Andy Walsh

Introduction

This article was the response by Andy Walsh to a discussion on the Internet Bonsai Club on the ability of plants to take up fertilizers. The hypothesis was that a plant would respond to ever increasing amounts of fertilizer by producing more and more roots and top growth.
BW

The Premise: More is Better?

It is correct to say that plants will make use of any resources they find in the soil. And it is tempting to assume from this, that adding more fertilizer will result in more growth. This would seem so, since most people have observed that plants grow more when they are fertilized. However this is not so.
Plants will differ greatly in their responses to soil nutrients which is dictated by their inherent growth rates, the duration of their growth periods, their ages, the types of root systems they have, and their ability to absorb nutrients.
Plants have widely different growth rates. Most of us who grow a wide variety of species know that some trees put out lots of growth and others crawl along. Increasing nutrient levels in the soil (fertilizing) will not change these inherent rates of growth. Compare the growth rates of the Trident maple with that of the Boxwood. If you apply equal amounts of fertilizer to a tree of each, that are of the same size and age, will you get the same amount of growth from both, that is, will they both assimilate the same amount of nutrients and incorporate them into new structures? The answer is no. The Boxwood will lag significantly behind the Trident in its amount of growth.
Even trees within the same genus have significantly different nutrient demands and will respond differently to nutrient levels in the soil. The growth of various pines during a season varies greatly in the amount of candle growth and the duration of the growth. White and Red Pines will reach 10 and 15 cm in candle growth by April and not increase significantly thereafter. Shortleaf, Slash, and Loblolly Pines will all reach 15 cm by April also but will continue growing until October by which time they will have reached 50, 60, and 90 cm in length respectively. (Biochemistry and Physiology of Plant Hormones", Thomas Moore).
It is well recognized by Bonsai growers that Pinus thunbergiana, the Japanese Black Pine, has a significantly different growth rate than Pinus parviflora, the Japanese White Pine. These two will never grow at the same rate or the same way. You cannot get a Japanese White Pine to grow like a Japanese Black Pine. So even within the limitations of a genus you will find differing responses to fertilizer levels.

Growth Effects of Increased Fertilizer

Increasing fertilizer does not elicit increasing growth rates even within a given plant either. The responses of many plants to increased fertilization have been very well studied especially in crop plants. There is a point of diminishing, or more appropriately, decreasing returns as fertilizer applications increase. In "Soils: An Introduction to Soils and Plant Growth" by Donahue et.al. shows a graph of plant growth response to increased fertilizer application. The curve is sigmoidal ("S" shaped) rather than linear. There is a plateau reached in the growth response as fertilizer increases and a drop off as it gets higher indicating that increasing fertilizer becomes more harmful than good. Donahue et.al. write:

"As more and more fertilizer is added, the gain in yields from each successive increment is less and less...The downward curve, as excessive fertilization increases, is due to reduced crop yields because of such things as salt problems and unbalanced growth (which may increase the plant's susceptibility to disease and abnormal growth)."

Optimum Amounts of Fertilizer

There definitely seems to be an optimal amount and regimen of fertilizer for each tree (that varies from tree to tree) and exceeding this can be harmful. Dr. Carl Whitcomb in "Plant Production in Containers" also warns about excessive and unbalanced fertilizer application. He writes "The optimum level of a plant nutrient is probably a limited range rather than a specific level. It should be noted that hidden...toxicities can occur long before...toxicity symptoms appear." He also shows a similar growth response vs. fertilizer curve.
I have read such caveats about excessive fertilizer applications in every reference I have on plant nutrition. Again, besides not directly increasing growth, increasing fertilizer levels can cause problems.

Seasonal Timing

Plant growth also differs in when and how long it takes place. There are some plants that put out new growth continuously throughout spring and summer, such as Juniper and Hinoki Cypress, and some that only put out new growth in the spring, such as Beech and Euonymous. Applying high amounts of fertilizer to all four trees may result in more growth in two of them but not in the other two. Adding high levels of fertilizer throughout the summer is certainly wasteful in the later instance since no new growth will be elicited.

Plant Maturity

Trees also differ in their overall growth depending on whether the plant is young or mature. The physiology of young trees is different than in older trees. Young trees tend to grow more rapidly and for longer periods of time. Some seedlings can double in size in a year. Many mature trees will only put out a small amount of new growth in the spring and stop growing early in mid-summer and actually start becoming dormant. (Older trees definitely have to slow down. Obviously a tree that doubles in size each year would be incredibly enormous if it maintained that rate for many years). Adding fertilizer to the soil will not make a tree that is going dormant reverse direction and start growing again. The amount and timing of nutrient uptake will be quite different in an older tree than in an immature tree and just raising the nutrient levels in the soil will not alter this either.

Absorption Rates According to Species

Plant roots also differ substantially in their ability to absorb different nutrients. For example, the ability to absorb magnesium can be as much as 60 times higher in one plant than in another. ("Russell's Soil Conditions and Plant Growth) This is a tremendous difference. One will suck it up and another will choke it down. Most of our Bonsai plants will not differ anywhere near this much but they will still differ significantly. In addition, the ability to absorb one nutrient can be adversely affected by high levels of another. The response to higher levels of nutrients is not equal, and again, high levels of fertilizer can lead to nutrient imbalances and unbalanced growth which can cause health problems with your trees.

And finally

These are some of the reasons that a simple equation of "more fertilizer = more growth" does not hold true.
For a simple analogy, think of the human condition. Can I force feed individuals with dwarfism and get them to grow more? Can I even get my son to grow more by making him eat all of his dinner (and as much as I eat)? He will only use as much food as he needs to grow and the rest will be stored as fat. He will not grow more. I can assure that both the individual with dwarfism and my son have enough nutrients to grow as much as they can - but not any more. I certainly can keep them from growing by limiting nutrients (the old fashioned way of growing Bonsai for that matter;) Neither my son, my father, nor I need as much food as a teenager. And we shouldn't get it. Obviously overfeeding anyone of these individuals is not only wasteful, but can be unhealthy for them also.
There is an old saying "All things in moderation" and this certainly applies to human life as well to fertilizer levels for Bonsai.

Creating a Forest Bonsai

by Brent Walston

Introduction

From a beginner point of view, this is an excellent early style, if not first tree, because the material involved is inexpensive, and usually readily available. In winter, bare root seedlings for forest plantings can be purchased in bulk for about $.35 to $.50 each. These trees usually come in bundles of 50 to 100. One could share an order with a friend or club members and obtain enough material for several group plantings and specimen trees alike.
Most of these bare root tree seedlings are field grown and will require the removal of the tap root and one year of pre-training prior to use as bonsai. I have described this process in the article on bare root pruning at our website.

Tree Arrangement

I spend a lot time thinking about tree placement to get the most natural looking arrangement, and have come up with some guidelines that I think work. First, it helps to have a concept of the scalene triangle outline used so much in bonsai. This is a triangle that often defines the outline of the foliage canopy. The elements of the triangle are three unequal length sides and no right (90 degree) angles. This will make a triangle which when viewed from the 'front' or main perspective that will have three levels defined by the corners. The points of the triangle can represent the position of elements, either trees in a forest, the three levels of the canopy, or the position of stones in a garden.
This group of three can be also be thought of as a group of two and one. A group of five can be envisioned as a group of three and two, or two groups of two and a group of one. Seeing the placement in groups three, or two and one can help one find pleasing positions for all the trees.
Another guideline I use is to never place a tree on the center line (through the front) or the mid line (that divides the front and back) of the pot. Trees placed in these positions will create a perfect symmetry that does not work as well as dynamic balance. I describe this as taking the visual mystery out of the space. Our eyes are very good at spotting whole number intervals, especial halves and quarters. We can actually do this with a high degree of precision. I think that what we do subconsciously is to dismiss these intervals when we detect them. Spaces that do not fall into easily easily defined intervals have more interest to us and 'move' as our brain tries to define the interval.
Trees should not fall directly behind one another when viewed from the front, and three or more trees should not fall on a single line. They may be placed tightly together at the middle of the pot with a rather large empty perimeter creating a 'knoll' look as found on hilltops, or be distributed in the pot giving more of a forest look.

Creating Perspective

The trees at the edges of the group can be placed leaning slightly outward to create perspective effects. This is almost a 'fish eye' lens image and tends to enhance and enrich the compactness of the forest. It also helps light to penetrate the center. This can be very subtle or exaggerated, each will give a very different look.
If the larger trees are placed in the front and the smaller ones in the back, this will also create perspective, with the view fading away as the eye goes through the forest.
The number one, two, and three trees are very important and must be placed carefully. They should diminish in height and caliper, and be positioned in a group of three. This works most easily if the number two and three trees are placed to the left and right of the number one tree. The remainder of the trees can be similarly small, but reserving the tiniest for the back.

Securing the Trees

Securing trees to the pot can be very challenging. In general, there must be some way of holding the trees in place until the roots knit together as one pad. From a styling perspective, anchoring makes the work a lot easier. For larger trees the general placement can be decided upon before the trees go in the pot and wires expoxyed to the bottom. A loop of wire can hold one root ball, or used to wire the trunks of two trees which will also hold them in place. For smaller pots I wire a large piece of stiff plastic mesh to cover the entire bottom instead of just the drain holes. Before securing it, I tentatively decide where the trees will go and loop wire through the holes to secure the trunks of two trees with one piece of wire.

Exploring Your Options

I find groups of three to be very challenging, for me it is easier to work with larger numbers. Even in small six inch pots I prefer to work with seven trees.
I have seen some very handsome groups where there are massive numbers of trees without clearly defined main trees, but I prefer the above approach. This is merely a matter of taste.
Placing the trees in groups as above should create unequal spaces between the trees for the 'birds to fly through' and often a space or shelter near the center of the pot near the number one tree. This is a resting place for the eye. I position the branches to invite the eye into this space.

Species Influence

Different species can create very different looking group plantings. For example, here I have compared Trident Maple, Acer buergerianum to Chinese Cork Bark Elm, Ulmus parvifolia 'Corticosa'. The example works for most maples and Chinese elms
Tridents, when planted in groves, have a very upright, soaring quality which is very pleasing. They will really give you the feeling of a natural forest mono culture typical of temperate hardwood regions. Getting spaces below the canopy will be very easy because they tend to bud break just below the cut when pruned.
Cork Bark Elm looks best, and is naturally inclined to be a round headed tree. As a grove, I would give them more space so that the character of each tree could develop. This look is typical of the open oak forests of California. The dome of each tree in these natural groves is usually clearly visible, even though they are grouped. The dark green canopies of these oaks against the golden dry grass of late summer is one of my very favorite sights in the whole world, and some day I hope to make a representation of this in bonsai.
The elms treated in this fashion would require larger trunks and shorter trees than Tridents, and more space between the trees to allow for the round headedness. It seems to me that this would be an appropriate situation for a large slab.

And finally

The scalene outline of the foliage is created by the entire canopy of all the trees instead of the main branches and apex of a single specimen bonsai. The highest point, of course, created by the number one tree, and the other two by the farthest left and right trees. To me, it is not too important to have either the left lower than the right or vice versa in a group planting. Many flattened dome outlines are perfectly satisfactory. My favorite view of forests is without the leaves anyway. The intricate branching of so many trees in a small pot is the real treat for me.