by Dave Bogan 

This article was taken from the  May 2007 Greater Evansville Bonsai Socity newsletter and is used with permission - ED.

Just when you thought you could relax, you now find that your Bonsai are in need of work. Depending on when you did your spring work, your trees are probably flushed with growth. By now, most all the leaves should be mature and hardened off and your tree is starting to look a little unruly. The time is right for you to now make a few decisions on its continued growth. By now, you should be pinching out the growth tips of most all branch areas. Keep in mind when doing this, you should pinch back into the canopy – deeper in than the desired outline of the canopy. If you simply pinch flush, you will be doing it again in a couple weeks and eventually you will notice the canopy is getting larger than planned. The key here is controlled pinching / pruning.

When pinching off leaves & or small branches, not only should you consider future elongation, you should consider the future growth direction. Remember that when a limb is cut or a leaf removed, the future branch direction will mimic the angle of the last leaf stem. In other words, if the relationship of the leaf stem to the branch was say 45 degrees and on the left side of the branch, the new branch will emerge at a 45 degree angle of the remaining branch and on the left side of the branch at the old leaf stem location. Thus, you can control length by how far back you cut and direction of new growth by the location of the last leaf stem behind the cut.

Next, you will need to consider leaf pruning – total or partially. Yes, there is a difference and each has its own end results.

Partial defoliation: Partial is the key work. In this case, partial also has different degrees. First, you need to understand from your tree just what is required. Does your tree simply have a lot of large leaves? Are some areas of the foliage thicker than others? Are some areas of the tree stronger than others? Depending on the above, you will need to remove some leaves.

A. Large leaves: Many of these were the first ones to appear when the tree first started to leaf out. These large leaves not only look out of proportion to others, they are also blocking a lot of light. In this case, simply remove the largest leaves all over the tree, thus allowing light & air to penetrate. This will help keep the inner areas of the tree from dying back. During the spring flush of growth, a lot of small branches and leaves appeared, many of which are now hidden behind these large leaves. If not allowed to have light, they will wither and die.

B. Strong areas: In this case, you may as above, remove all the large leaves but also remove more leaves in the strong areas. By removing more in the strong areas, it will temporarily slow these areas down and divert the strength to other (weaker) areas.

C. Weak Areas: Just the opposite of the strong areas. Try not to touch these areas a lot. Even if they grow out past the outline, it is better to let them grow and build strength. You must also attempt to determine why these areas are weak. Look for insect signs. Are some of the leaves chewed on? What is their color compared to the rest of the tree? Typically if their color is different for the rest of the tree, you have serious problems. Maybe the branch was accidentally cracked or broken? Many times, a weak area can be attributed to a root problem. Did you cut heavily on the roots directly below these areas? Hopefully if you have excluded pest problems, by allowing this area to continue growing unchecked, it will gain strength and be fine - Time will tell.

On a health note, always keep a close eye on the leaf color and the general strength of the tree. If you notice a dull color, it could be attributed to nutrition. Hopefully, you have a fertilization program in place. If nothing else, fertilize at set intervals. Even if you are fertilizing, you could still have a deficiency. Look into adding micronutrients to your trees. There are several products that have trace nutrients and vitamins. Superthrive is a good product available at most garden centers. The use of organic additive can also help. I like using products derived from kelp & sea products. Fish emulsion is a great additive. Next, you need to consider some mineral additives. Iron deficiencies are very common. A simple addition of a cheted iron product will help in foliage coloration. Foliar sprays can help quickly. Plants will take in almost all types of additives via their foliage quicker than through their root systems. Even the addition of Epson salts via a foliar spray will help. After determining deficiencies, always keep a close eye out for insect problems. A die back of one area in the tree can be attributed to a problem in the roots. It could be soil born insect larvae or hopefully not, a problem with fungus in the root system. When in doubt, drench the soil with a systemic insecticide and later a drench of a good fungicide can be very beneficial.

Full Defoliation: This procedure is used to gain ramification and a fuller look. Do NOT consider it a way of reducing leaf sizes. Leaf size reductions will sometime result from defoliation, but actually it is a result of proper health and more branches and a finer root system. We remove all the leaves on a tree in order to create a second flush of growth. Let’s say, back in spring when you worked on the tree, there was say 100 branches. Now, 6 – 8 weeks later, there are over 200 branches. By removing a leaf, it activates the dormant buds laying at the intersection of the leaf and branch. So, with 200 branches, each branch having say 6 leaves, we have just activated 1200 dormant buds which will be come 1200 new branches. Can you imagine how much fuller your tree is going to look? Sure, of the 1200 new branch possibilities, maybe only 900 will sprout. Of this 900, maybe only 600 will live to maturity.

Let's go even further and say that only 400 of these will live. You have, at minimum, doubled the amount of branches and leaves on your tree after a successful leaf pruning session. Now, the tree has had to expend a lot of energy, and this energy must now be channeled to a lot more locations than previously; so, the resulting leaves will be small, based on available energy reserves. Another huge factor is the need to obtain nutrients and light. Some way, the tree knows it will now have a lot more receptors (leaves); so, based on demand and quantity, the leaves can be much smaller and still supply all the needs of the tree. Thus, this set of leaves is smaller than the previous set. As the tree increases its fine branch and leaf structure, it also develops a finer root structure. Through all this, you have created a Bonsai or a dwarfed tree in a pot. So, with a little help from man, the tree has become more efficient.

In some areas, and dependent on the species, some trees are defoliated more than once a year. You will need to use your judgement here. Timing and the health of the tree will dictate how often you perform this work. Timing can be a huge factor. If you perform this work too late, the tree will not have the energy to totally refoliate before fall or the time when the tree diverts its growth from upper growth to below ground growth and storing energy for the coming fall / winter season. From experience, I have defoliated some maples (trident) twice in the same year. But, I now do it only once a year. I have experienced weak re-foliating in some trees. So I say, why rush things and potentially weaken the trees?

Tips on How to Defoliate
Removing every leaf on a tree can be a very time-consuming task. Here’s a little trick on how to remove the leaves; test a few leaves first. On many long stemmed leaves, you can simply pull them off instead of cutting everyone. Grasp the leaf and pull. If the leaf comes off leaving part of the stem, you do not need to cut them. The main objective is to not tear or damage the very small bud lying at the base of the leaf stem. If damaged, it will not grow. Some trees like Chinese elms are tough. Their leaf stems are only a fraction of an inch long. Careful plucking will work, but on this species, if in doubt, cut them. A species that has no problem with plucking is most all the ficus species. The leaves pull away easily, leaving the stems behind. Some, like the green island, have tougher leaves and sometimes the stems will not break. In the case of the ficus, you will get your fingers covered with the sticky sap and occasionally need to wash your hands, since they will get sticky after a while. Another tropical that is some what easy is the Portulacaria (miniature jade) even though their leaves are soft they will pull away leaving a stem. On species like the portulacaria, you will need to hold the branch, as it will break easily if pulled on too hard. Try this and I’m sure you will find defoliating a tree will be a lot easier and much quicker.

I have heard stories of people using cold air on tropicals (makes all the leaves fall off) or even using wind power. I once heard Dan Robinson talk of setting his trees on a board above the cab of his truck and driving down the road. Both of these techniques are a little abusive and may damage the trees in other ways. I think I will avoid all techniques except those where I use scissors or my fingers.