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 got
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 University Cooperative
Extension Service, West Lafayette, IN
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
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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. .