U n i v e r s i t y   C o o p e r a t i v e   E x t e n s i o n   S e r v i c e ,   W e s t   L a f a y e t t e ,   I N
U n i v e r s i t y   C o o p e r a t i v e   E x t e n s i o n   S e r v i c e ,   W e s t   L a f a y e t t e ,   I N
Everything they taught you in pruning school is wrong. Well, maybe not everything.  Let me make it clear that this is about pruning bonsai – not yard trees.  This is not for arborists or arborist wannabees.  And some of the things they say are correct.  But we are styling bonsai - not 10 to 100 foot trees - and we are styling and shaping our trees so we have very different objectives.  So if you wandered onto this site from thru an internet search and want information about lawn trees, go elsewhere.  Many of the pictures below are adapted from the internet and were correct in their context. The Goals of pruning There are many different reasons that we prune bonsai and each reason has a different technique.  Our trees are small (small is a relative term and one can see the different sizes of bonsai on another page) and there must be routine pruning to maintain the size and shape we desire while promoting the health of the tree.  When making heavy cuts for styling different rules will apply.  There are quite different goals and thus procedures for making styling cuts on deciduous versus conifers.   More correctly I should say plants with and without jin and shari or plants where we want wounds to heal completely or plants where deadwood is a feature of the plant.   Maintenance Pruning Maintenance pruning should consist of many small cuts all over the tree and none of those cuts will require wound care.  They are usually done with scissors or by finger plucking.  The majority of that work comes in the spring, though it is ongoing throughout the growing season.  There should be visible lightening or opening up of the tree.  Branches and leaf pads should be better defined.  A bird should be able to fly thru the tree.  The most simple maintenance pruning is the daily or weekly pinching of buds where they are unwanted or unneeded.  The new growth on junipers can be pinched back every day you look at them because there is always more to come.  Long shoots of new growth should generally be cut back to encourage branching.  After flowering, every single flower bud should be pinched off of azaleas, so you pay dearly for a year when they are covered with flowers.  One switches from finger-tip pinching to fine scissors on going to maples, elms, crepe myrtles and others.  In the spring, maples want to put on lots of new growth.  There can be two, three, or more pair of leaves on a greenwood maple shoot.  It is important to get the shoot clipped back to the first pair of leaves quickly because the entire length of the green shoot is extending as it puts new growth on the end.  The first pair of leaves might be tight to the branch when there are only two pairs of leaves on the shoot, but if you wait until there are four or more pair of leaves, the first two leaves will be much farther from the branch.  Good ramification requires constant pruning.  On maples, it is also important to cut the stem back very close to the pair of leaves.  One will expect to get two new branches when trimming back to a pair of leaves.  If the cur is farther down the stem, the twig will die back to the point of the new branches but will remain on the tree and be unsightly.  It will probably drop off in the next season, but why wait when more careful trimming will take care of it immediately?  The next level of maintenance pruning involves cutting back small branches.  If there are a series of buds down a branch, you might want to prune back to just a few.  The cut in Figure 1A is cut too high, but for bonsai, so is the cut in Figure 1C which is recommended by arborists.  The best cut in this case is the middle one (Figure 1B) and where the initial cut appeared to be a bit higher, but then a second, more horizontal cut removed a bit of the remaining point above the bud.  The middle cut, properly trimmed, will heal nicely putting a curve into the branch at that point as the remaining bud becomes the new leader.  Hopefully, there are several additional buds farther back the branch to provide additional branching There are few trees that reduce as well as Chinese elm (ulmus parvifolia), but this requires careful pruning.  In nature, the leaves are up to two inches long.  With constant pruning to maintain very small branches, the leaves can be maintained at less than half an inch.  The elm provides a very good illustration of why maintenance pruning is important.  In the spring, when the new shoots first start, the first two leaves can be under a quarter of an inch and each successive leaf will be larger, going out the shoot.  If one keeps the tree trimmed back so that every branch tip has only two to four leaves, then all of the leaves will have the desired diminutive size.  Letting runners go will fatten up a branch more quickly, but there will be a price to pay in leaf size.               Defoliation What arborist is ever going to tell you that you should cut all of the leaves off your tree?  You would laugh them out of your yard or maybe report them to the Better Business Bureau.  Complete defoliation of a tree may seem like a drastic step but there are times where it can be quite beneficial.  In the late spring when a maple is lush with new growth, it is possible to remove all of the leaves and much of the greenwood.  This step will promote back-budding to generate a considerable number of new small branches.  Leaf sizes on the new branches will be considerably smaller than before the defoliation.  I have several shohin maples that have leaves that are disproportionately large.  Annual defoliation keeps the leaves in proportion to the tree.  Finally, I must admit to several accidental defoliations.  Most of my better trees are protected by a fence, but some trees in progress are on benches exposed to deer.  If I am on vacation, my trees are watered automatically, but not if a deer has pulled the tree off the bench.  On more than one occasion I have found completely dehydrated maples lying on the ground.  The leaves may be crunchy, but if the tree is cared for, it will come back and there will be new buds at the point of most of the old leaves.  The new foliage will be delightfully small.  This is an effective but not a recommended  procedure.  Pruning for Healing Pruning for healing is the objective for all arborists.  Pruning for healing is the objective for deciduous trees and pines where the objective is to have the wound heal over completely and blend into the silhouette of the tree.  For good healing, it is imperative that one get a good clean cut with no ripping of the bark.  If one is using scissors to make the cut, then there is now issue with the wound.  If one is using a diagonal or concave cutter, then the branch is small enough and the cut is quick enough that there will ne no ripping of bark.  If there is any straining with the cutter, then the cur is big enough that the branch should be cut with a first cut leaving a knob and then go back and finish the cut approaching the trunk carefully and making sure the bark around the cut has a good clean edge for improved healing.  If the cut is large enough that one is going to use a saw, then one should use the arborist method using a three-cut approach.  The three-cut method shown in the figure is the best way to initiate the cut.  Cut A is to protect the bark below the cut.  Cut B removes the branch.  Cut C provides the final wound that an arborist would prefer because it heals quickly.  The arborist will stop here expecting the branch to heal over, being unconcerned about the resulting knob on the tree.  It is pointed out that cutting any closer to the tree will damage the “healing ring” around the branch.  The three-cut technique shown is an issue in bonsai because it leaves an aesthetically unappealing knob on the tree.  That is the reason that we have concave or knob-cutters.  For a thick-skinned tree a flush cut might suffice but for a tree that develops a strong callous, a concave cut is required.  Hollowing out the wound slightly will leave space for the thick fleshy callous.  As a result we are required to damage the healing ring which will make healing more difficult.  The first next step for a good bonsai cut is to clean up the edges of the wound with a very sharp knife or razor blade.  Smoothing the wound promotes healing all the way around.  Finally, the wound on bonsai should be covered with a flexible cut paste even though the tree industry now recommends against covering wounds.                             A                                B                                C                                    D Figure3:  Four examples of branch cuts.  A) A cut that would make an arborist cringe, but in fact, it is a perfectly suitable cut for a bonsai showing deadwood.  B) A cut that is unsuitable in all cases.  Three-cut pruning described above avoids this worst case.  C) The arborists perfect cut that will heal well.  It will leave an unsightly knob on a bonsai.  D) A bonsai cut that will heal nicely leaving a minimal scar on the tree.  The cut may be flush or slightly concave and the edge of the wound is cleaned up with a sharp knife.  Deadwood There is no way an arborist would want to generate deadwood on a tree – but it is an essential part of several bonsai styles.  The reason that we do junipers is for the drama of deadwood to show what a difficult life the tree has survived.  Jin on branches and shari down a trunk are the two types of deadwood.  Usually, a tree should have neither or both.  The death of a branch will often lead to death of the live vein that fed it so jin should often lead to shari.  And there is seldom only one piece of jin on a tree.  Arborists do their three-cut pruning so that the live vein below a branch is not injured, but in nature branches are ripped off trees by the weight of snow or by wind.  There should be purposeful generation of shari below a broken branch.  Jin is easily generated by cutting a branch off some distance from the trunk.  Squeeze the branch with pliers to crush the cambium layer.  After crushing, it will generally peel off the branch quite easily.  Feel free to pull the bark right down the trunk to create a scar below the branch – this is the way it looks in nature.  There is nothing as unnatural as a dead branch with a perpendicular cut on the end, so after peeling the bark, grab the branch in your pliers and twist it to create a jagged break.  If it is too large to be broken, peel off strips of wood, mostly from the bottom side, to leave a raw jagged look.  Long thin jin means that the branch has died recently.  We want trees to look old, so the jin should look aged and this is achieved by making it shorter relative to the diameter of the trunk.  After jin and shari have been aged for a while, they should be painted with relatively concentrated lime sulfur.  At first, this will result in unnatural-looking yellow deadwood, but within days, the lime sulfur will turn white.  Deadwood in the high Rockies can be very white, but if this it too white for your sensibilities, it can be toned down a bit with a wash of very dilute, black India Ink.  Stumping Stumping is something that no arborist will do.  Their nearest term for it is “cutting down the tree.”  For them, it is a terminal act.  Any shoots that come up from the stump are an unwanted nuisance and they will often grind out the stump to remove any evidence of the existence of the tree.  Though not for the feint-of-heart, stumping can be a useful technique in bonsai.  It is the act of cutting the tree back to a useful section of trunk – no branches – and praying for new buds to form around the cut.  Stumping should generally be carried out in the spring before the tree has wasted any energy on new growth because it is going to need everything it has to push out sufficient new growth from the stump.  There are mixed messages about how to promote new growth.  I simply seal the cut and often wrap the edges with plastic tape to force all of the new growth vertical rather than have it bur our horizontally.  Others suggest that the cut be kept moist with wet cotton or sphagnum until the buds are well established.  The technique works well with maples, elms, hornbeams and zelkova.  They bud reliably around the cut and the issue is likely to be which of the many buds do you keep and which buds to you rub off.  Leave a lot if you are headed toward a broom style with an elm.  Keep just two if you want a new trunk with a single side branch.  It is possible to purchase stumped trident maples online and these can lead to trees with quite dramatic taper in a short period of time.  While spring is the optimal time for making stump cuts, I have also done it successfully with a lovely maple in my yard that deer decided to use for rubbing the felt off their antlers.  The tree was girdled and the top of it quickly dried to a crisp.  I cut it back to a stump and sealed the wound with cut paste.  In the following spring, it pushed many new branches around the cut and is now a nice bonsai.  You have been told that conifers cannot be cut back beyond the last green, so they should not be candidates for stumping.  Nonetheless, I have successfully stumped a white pine.  It was two inch diameter and was cut back to 4 inches tall.  Rather than pushing new branches around the cut like deciduous, the new branches pushed out of the bark all around the trunk in a two inch band starting from the cut.  There were far too many branches, but they were all allowed to grow until the tree gets over the shock.  References: 1.  hhp://iredell.ces.ncsu.edu 2.  Pruning Ornamental Trees and Shrubs, Michael Dana and Philip Carpenter, Department of Horticulture, Purdue
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Figure 2:  Three-cut pruning.  The initial cut (A) should be an undercut to protect the bark on the branch.  The second cut (B) removes the branch taking the strain off the joint.  An arborist will tell you to make the third cut at (C) but that will leave an unsightly but healthy wound.  Cutting flush at (D) will be more difficult to heal, but will leave a better looking tree in the end.
Pruning Bonsai
Brandywine Bonsai Society is an educational organization and as a result, the material in this site may be copied for educational purposes.  If large portions are copied, we would appreciate attribution.  We welcome links to this site. 
                 A                                  B                               C Figure 1:  Pruning twigs.  A) is pruned to far above the twig; B) is a double cut for bonsai where the initial diagonal cut left a point above the bud which was cut off in a second cut; C) is the cut recommended by an arborist.                             .
Everything they taught you in pruning school is wrong. Well, maybe not everything.  Let me make it clear that this is about pruning bonsai – not yard trees.  This is not for arborists or arborist wannabees.  And some of the things they say are correct.  But we are styling bonsai - not 10 to 100 foot trees - and we are styling and shaping our trees so we have very different objectives.  So if you wandered onto this site from thru an internet search and want information about lawn trees, go elsewhere.  Many of the pictures below are adapted from the internet and were correct in their context. The Goals of pruning There are many different reasons that we prune bonsai and each reason has a different technique.  Our trees are small (small is a relative term and one can see the different sizes of bonsai on another page) and there must be routine pruning to maintain the size and shape we desire while promoting the health of the tree.  When making heavy cuts for styling different rules will apply.  There are quite different goals and thus procedures for making styling cuts on deciduous versus conifers.   More correctly I should say plants with and without jin and shari or plants where we want wounds to heal completely or plants where deadwood is a feature of the plant.   Maintenance Pruning Maintenance pruning should consist of many small cuts all over the tree and none of those cuts will require wound care.  They are usually done with scissors or by finger plucking.  The majority of that work comes in the spring, though it is ongoing throughout the growing season.  There should be visible lightening or opening up of the tree.  Branches and leaf pads should be better defined.  A bird should be able to fly thru the tree.  The most simple maintenance pruning is the daily or weekly pinching of buds where they are unwanted or unneeded.  The new growth on junipers can be pinched back every day you look at them because there is always more to come.  Long shoots of new growth should generally be cut back to encourage branching.  After flowering, every single flower bud should be pinched off of azaleas, so you pay dearly for a year when they are covered with flowers.  One switches from finger-tip pinching to fine scissors on going to maples, elms, crepe myrtles and others.  In the spring, maples want to put on lots of new growth.  There can be two, three, or more pair of leaves on a greenwood maple shoot.  It is important to get the shoot clipped back to the first pair of leaves quickly because the entire length of the green shoot is extending as it puts new growth on the end.  The first pair of leaves might be tight to the branch when there are only two pairs of leaves on the shoot, but if you wait until there are four or more pair of leaves, the first two leaves will be much farther from the branch.  Good ramification requires constant pruning.  On maples, it is also important to cut the stem back very close to the pair of leaves.  One will expect to get two new branches when trimming back to a pair of leaves.  If the cur is farther down the stem, the twig will die back to the point of the new branches but will remain on the tree and be unsightly.  It will probably drop off in the next season, but why wait when more careful trimming will take care of it immediately?  The next level of maintenance pruning involves cutting back small branches.  If there are a series of buds down a branch, you might want to prune back to just a few.  The cut in Figure 1A is cut too high, but for bonsai, so is the cut in Figure 1C which is recommended by arborists.  The best cut in this case is the middle one (Figure 1B) and where the initial cut appeared to be a bit higher, but then a second, more horizontal cut removed a bit of the remaining point above the bud.  The middle cut, properly trimmed, will heal nicely putting a curve into the branch at that point as the remaining bud becomes the new leader.  Hopefully, there are several additional buds farther back the branch to provide additional branching There are few trees that reduce as well as Chinese elm (ulmus parvifolia), but this requires careful pruning.  In nature, the leaves are up to two inches long.  With constant pruning to maintain very small branches, the leaves can be maintained at less than half an inch.  The elm provides a very good illustration of why maintenance pruning is important.  In the spring, when the new shoots first start, the first two leaves can be under a quarter of an inch and each successive leaf will be larger, going out the shoot.  If one keeps the tree trimmed back so that every branch tip has only two to four leaves, then all of the leaves will have the desired diminutive size.  Letting runners go will fatten up a branch more quickly, but there will be a price to pay in leaf size.               Defoliation What arborist is ever going to tell you that you should cut all of the leaves off your tree?  You would laugh them out of your yard or maybe report them to the Better Business Bureau.  Complete defoliation of a tree may seem like a drastic step but there are times where it can be quite beneficial.  In the late spring when a maple is lush with new growth, it is possible to remove all of the leaves and much of the greenwood.  This step will promote back-budding to generate a considerable number of new small branches.  Leaf sizes on the new branches will be considerably smaller than before the defoliation.  I have several shohin maples that have leaves that are disproportionately large.  Annual defoliation keeps the leaves in proportion to the tree.  Finally, I must admit to several accidental defoliations.  Most of my better trees are protected by a fence, but some trees in progress are on benches exposed to deer.  If I am on vacation, my trees are watered automatically, but not if a deer has pulled the tree off the bench.  On more than one occasion I have found completely dehydrated maples lying on the ground.  The leaves may be crunchy, but if the tree is cared for, it will come back and there will be new buds at the point of most of the old leaves.  The new foliage will be delightfully small.  This is an effective but not a recommended  procedure.  Pruning for Healing Pruning for healing is the objective for all arborists.  Pruning for healing is the objective for deciduous trees and pines where the objective is to have the wound heal over completely and blend into the silhouette of the tree.  For good healing, it is imperative that one get a good clean cut with no ripping of the bark.  If one is using scissors to make the cut, then there is now issue with the wound.  If one is using a diagonal or concave cutter, then the branch is small enough and the cut is quick enough that there will ne no ripping of bark.  If there is any straining with the cutter, then the cur is big enough that the branch should be cut with a first cut leaving a knob and then go back and finish the cut approaching the trunk carefully and making sure the bark around the cut has a good clean edge for improved healing.  If the cut is large enough that one is going to use a saw, then one should use the arborist method using a three-cut approach.  The three-cut method shown in the figure is the best way to initiate the cut.  Cut A is to protect the bark below the cut.  Cut B removes the branch.  Cut C provides the final wound that an arborist would prefer because it heals quickly.  The arborist will stop here expecting the branch to heal over, being unconcerned about the resulting knob on the tree.  It is pointed out that cutting any closer to the tree will damage the “healing ring” around the branch.  The three-cut technique shown is an issue in bonsai because it leaves an aesthetically unappealing knob on the tree.  That is the reason that we have concave or knob-cutters.  For a thick-skinned tree a flush cut might suffice but for a tree that develops a strong callous, a concave cut is required.  Hollowing out the wound slightly will leave space for the thick fleshy callous.  As a result we are required to damage the healing ring which will make healing more difficult.  The first next step for a good bonsai cut is to clean up the edges of the wound with a very sharp knife or razor blade.  Smoothing the wound promotes healing all the way around.  Finally, the wound on bonsai should be covered with a flexible cut paste even though the tree industry now recommends against covering wounds.                             A                                B                                C                                    D Figure3:  Four examples of branch cuts.  A) A cut that would make an arborist cringe, but in fact, it is a perfectly suitable cut for a bonsai showing deadwood.  B) A cut that is unsuitable in all cases.  Three-cut pruning described above avoids this worst case.  C) The arborists perfect cut that will heal well.  It will leave an unsightly knob on a bonsai.  D) A bonsai cut that will heal nicely leaving a minimal scar on the tree.  The cut may be flush or slightly concave and the edge of the wound is cleaned up with a sharp knife.  Deadwood There is no way an arborist would want to generate deadwood on a tree – but it is an essential part of several bonsai styles.  The reason that we do junipers is for the drama of deadwood to show what a difficult life the tree has survived.  Jin on branches and shari down a trunk are the two types of deadwood.  Usually, a tree should have neither or both.  The death of a branch will often lead to death of the live vein that fed it so jin should often lead to shari.  And there is seldom only one piece of jin on a tree.  Arborists do their three-cut pruning so that the live vein below a branch is not injured, but in nature branches are ripped off trees by the weight of snow or by wind.  There should be purposeful generation of shari below a broken branch.  Jin is easily generated by cutting a branch off some distance from the trunk.  Squeeze the branch with pliers to crush the cambium layer.  After crushing, it will generally peel off the branch quite easily.  Feel free to pull the bark right down the trunk to create a scar below the branch – this is the way it looks in nature.  There is nothing as unnatural as a dead branch with a perpendicular cut on the end, so after peeling the bark, grab the branch in your pliers and twist it to create a jagged break.  If it is too large to be broken, peel off strips of wood, mostly from the bottom side, to leave a raw jagged look.  Long thin jin means that the branch has died recently.  We want trees to look old, so the jin should look aged and this is achieved by making it shorter relative to the diameter of the trunk.  After jin and shari have been aged for a while, they should be painted with relatively concentrated lime sulfur.  At first, this will result in unnatural-looking yellow deadwood, but within days, the lime sulfur will turn white.  Deadwood in the high Rockies can be very white, but if this it too white for your sensibilities, it can be toned down a bit with a wash of very dilute, black India Ink.  Stumping Stumping is something that no arborist will do.  Their nearest term for it is “cutting down the tree.”  For them, it is a terminal act.  Any shoots that come up from the stump are an unwanted nuisance and they will often grind out the stump to remove any evidence of the existence of the tree.  Though not for the feint-of-heart, stumping can be a useful technique in bonsai.  It is the act of cutting the tree back to a useful section of trunk – no branches – and praying for new buds to form around the cut.  Stumping should generally be carried out in the spring before the tree has wasted any energy on new growth because it is going to need everything it has to push out sufficient new growth from the stump.  There are mixed messages about how to promote new growth.  I simply seal the cut and often wrap the edges with plastic tape to force all of the new growth vertical rather than have it bur our horizontally.  Others suggest that the cut be kept moist with wet cotton or sphagnum until the buds are well established.  The technique works well with maples, elms, hornbeams and zelkova.  They bud reliably around the cut and the issue is likely to be which of the many buds do you keep and which buds to you rub off.  Leave a lot if you are headed toward a broom style with an elm.  Keep just two if you want a new trunk with a single side branch.  It is possible to purchase stumped trident maples online and these can lead to trees with quite dramatic taper in a short period of time.  While spring is the optimal time for making stump cuts, I have also done it successfully with a lovely maple in my yard that deer decided to use for rubbing the felt off their antlers.  The tree was girdled and the top of it quickly dried to a crisp.  I cut it back to a stump and sealed the wound with cut paste.  In the following spring, it pushed many new branches around the cut and is now a nice bonsai.  You have been told that conifers cannot be cut back beyond the last green, so they should not be candidates for stumping.  Nonetheless, I have successfully stumped a white pine.  It was two inch diameter and was cut back to 4 inches tall.  Rather than pushing new branches around the cut like deciduous, the new branches pushed out of the bark all around the trunk in a two inch band starting from the cut.  There were far too many branches, but they were all allowed to grow until the tree gets over the shock.  References: 1.  hhp://iredell.ces.ncsu.edu 2.  Pruning Ornamental Trees and Shrubs, Michael Dana and Philip Carpenter
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Figure 2: should be an undercut to protect the bark on the branch.  The second cut (B) removes the branch taking the strain off the joint.  An arborist will tell you to make the third cut at (C) but that will leave an unsightly but healthy wound.  Cutting flush at (D) will be more difficult to heal, but will leave a better looking tree in the end.
Pruning Bonsai
Brandywine Bonsai Society is an educational organization and as a result, the material in this site may be copied for educational purposes.  If large portions are copied, we would appreciate attribution.  We welcome links to this site. 
                 A                                  B                               C Figure 1:  Pruning twigs.  A) is pruned to far above the twig; B) is a double cut for bonsai where the initial diagonal cut left a point above the bud which was cut off in a second cut; C) is the cut recommended by an arborist.                             .