Bonsai pruning is necessary to create your desired style and maintain the size and form of your tree. It is an important part of the bonsai art and is also essential to encouraging new growth and preserving the health of the plant.
Basically, there are two types of pruning: structural and maintenance.
Structural bonsai pruning is usually done when the tree is young and needing to be trained for a specific bonsai style. Since it involves major changes and the removal of primary branches, it can put the tree under a lot of stress. For this reason, it is very important that it only be done at the right time of year, usually in the Spring or Autumn, when the tree is in dormancy. The amount of heavy pruning that can be done will depend on the species, the time of year, and the recovery conditions.
Maintenance bonsai pruning can be done all year round, although it will be more necessary during the growth season, as this is when you tree will be most likely to deviate from its shape or form. The purpose of this type of pruning is to ensure that your bonsai maintains its size and style, and to encourage new growth or more blossoms. Also, since most new growth is on the top or outer part of the tree, pruning these areas regularly will allow more foliage to develop on the inner parts of the plant. The most aggressive maintenance pruning is usually done in the Spring and Fall, although small refinements may be needed throughout the year.
Types of Bonsai Pruning
Leaf and Shoot Bonsai Pruning:
This is one of the most important steps of the pruning process because without it, your bonsai will lose its shape and quickly outgrow its container or pot.
Leaf and shoot bonsai pruning can be done anytime during the growing season, whenever you notice that new growth is affecting the shape of the tree or giving it an unbalanced appearance.
Using a pair of sharp, long-handled scissors, cut shoots back to just after the next set of leaves. Some shoots can have up to 5-6 series of leaves, and it is recommended that you trim to about 2 sets of leaves.
It is important that you take care not to cut any foliage. This is sometimes also referred to as tip pruning. By cutting away long shoots, you will not only be regaining the intended shape, but within a few weeks you will begin to notice the development of new shoots with reduced leaf size as well as increased ramification (branch splitting). This is designed to keep your bonsai more proportionate in size and give it a more natural look.
Leaf pruning is usually done after the first set of new leaves has fully matured. Using a sharp pair of scissors, leaf pruners, or shears, cut the leaves at the point where they attach to the stalk, leaving the stem (petiole) on the tree.
The petiole will eventually fall off and a replacement set of leaves will grow, with smaller size and increased ramification and density. This is also referred to as defoliation. All leaves may be removed from the tree, or only selected branches can be defoliated.
Sometimes, individual leaves may also be pruned if they are too large. Simply fold the leaf in half along the stem, then cut the top of the leaf off on an angle so that when the leave is unfolded it will come to a point, or an inverted “V”. leaves can be reduced to about 1/3-1/2 of their original size.
Make sure to leave foliage on weak areas of the tree to promote growth in that area. It is also important that you only perform heavy defoliation at certain times of year to ensure that your bonsai is able to recover properly.
Branch Bonsai Pruning:
Growth tends to be concentrated at the top or the outside of a tree. Sometimes you will need to prune the crown of your bonsai so that light and air can reach the lower branches or inner leaves. This may require pruning branches rather than just shoots or leaves. Branch pruning will also help you control the growth and development of the tree while you are shaping and training it.
First, decide which branches need to be removed and then mark them with a marker so that you know where to cut. Use a pair of bonsai scissors or branch cutters to shorten limbs or remove thinner branches. Be sure to cut across a diagonal of the stem as this gives a more natural cut.
For the removal of thicker branches, use a concave branch cutter, which will leave a curved indentation, allowing the wound to heal without scarring. If you want a branch to grow in a particular direction, be sure to cut it above a bud that is facing that direction.
While you are pruning, use knob cutters to remove any deadwood or stubs that may still be there from previous years. Remember to cover all wounds with a paste to prevent sap loss, decrease risk of infection, and promote healing.
If you do a major amount of pruning, it is important that you also cut the roots back in equal proportion, otherwise your bonsai may experience sudden growth to correct the imbalance between foliage and roots.
Bud Pruning or Pinching:
While leaf pruning is typically for deciduous trees, pinching is usually used when de-budding conifers. By removing the tips of the growing needles, you will encourage increased branching and also help the bonsai to maintain its compact design.
Pinching should be done when excessive growth of needles causes the tree to lose its desired shape. Often branches can have as many as six new buds and, as with its deciduous counterparts, this should be pruned back to two budding needles that are growing in the appropriate direction. Using scissors or bonsai cutters will cause dead or brown foliage on conifers, so finger pinching is recommended.
Hold the tip of the shoot or new growth between your thumb and forefinger, and carefully pluck it away. You may have to support the branch with your other hand to stabilize the plant and ensure that you only pull off what you desire.
Bonsai Pruning Tips
If two branches are beside each other or growing at the same height, remove one and keep the other.
Remove branches that are too thick or growing in a vertical direction.
Remove twisted or misshapen branches.
Remove branches that are too low or conceal the trunk.
Cut back branches at the top of the tree that are thicker than those at the bottom of the plant.
Cut off spindly or unhealthy looking branches.
Shorten or trim branches that are too long or affect the overall style of your bonsai. The goal is to achieve a triangular shape.
Make sure to do heavy pruning at the right time of year, usually spring or fall when the plant is in its dormant season. Inappropriate pruning can cause damage and your bonsai may never recover.
Leave extra leaves or branches on the weak area of the trunk to promote new growth in that area.
Remove or prune large leaves so that your tree will be forced to replace them with smaller foliage.
Remember to cut back root systems in direct proportion to the “above ground” pruning.
Always use sharp tools to prune your bonsai. Blunt tools can cause damage to branches and leaves.
Give your bonsai proper care after pruning. Water it well, and put it in a shaded location where it will be protected from the elements. Remember to use wound sealant on major cuts to prevent infection. Allow your plant to recover for at least a couple of months before doing any additional heavy pruning.
Don't be afraid to prune your tree. The more you trim back, the fuller your bonsai will become.
Bonsai pruning is necessary to give your tree its desired shape and style, and to help maintain its overall size and appearance. But remember, bonsai is an art that that not only reflects nature, but also represents the unique styling of the artist.
While certain techniques will help preserve your tree's health, styling guidelines are only suggestions, not hard and fast rules. As long as your bonsai is happy and healthy, it is alright to let your creative juices flow!