Established young tree is fair game
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Wait until tree's established
Take off only damaged branches until a new tree becomes
established. That usually takes about one year for each inch of
trunk diameter at planting time.
We know a tree's established when it resumes growing as many
inches per year as it can. Compare the current year's growth to how
much it was growing each year in the nursery.
Choose
main limbs: Allow each its own piece of the sky
Once the tree is established, clip away. Focus on the
far
future. The branches you leave should be
gracefully
arranged to fill out but not compete for the canopy's
north, south east and west sections.
Left: This little oak had what's called double barrel
or
shotgun branches -- limbs of equal size
positioned
to try to fill exactly the same part of the sky.
We removed one.
If both were left in place they would develop into
what
you see on the mature tree (below, right). It makes
an
unbalanced crown and causes the tree to grow twice as
much wood (an energy drain) to capture the same
amount of sun (a plant's sole source of energy) that
a
single limb could claim.
Elevate with the future in
mind
Remove lower branches until what remains is high enough above
ground to allow plenty of headroom. We aim for a park-like feel,
with shade but enough air movement to make picnickers happy and
enough light to keep grass growing. So we prune away lower limbs
year by year until at last we are standing on a step ladder to do
this work.
Branches do not move up on a trunk as a tree grows. The trunk
and the branch both increase in girth, and each add to their
length, but a branch that joined the trunk at four feet from the
ground will always be four feet from the ground. At any rate, its
center will be there. Since it will increase in diameter,
its lower edge may eventually be closer to the ground than
when it first formed.
Below: Although Janet's reaching over her head to elevate
the tree -- remove lower limbs. -- it's not enough. We'll do it
again after the tree grows taller, and again until the trunk is
clear for ten feet or more because we aim for the kind of high
canopy on the old double barrel oak.
The one-third rule: How
it evolved, and applies
As you figure which branches you'll remove, estimate how many
buds that will take away from the tree. Try to leave twice as many
buds on the tree as are in your clippings pile. That's in keeping
with the recommendation that we take away no more than 1/3 of a
tree's foliage in any year.
This isn't a hard, fast rule. Yet it's a good guide if we want
to leave a young tree with plenty of energy and avoid simulating it
to sucker wildly.
Why 1/3? Most plants can produce enough energy with one leaf to
make three the next year. With that energy they can replace in
spring all that they dropped in fall, add an equal number of new
leaves, and still have energy in reserve in case leaves are lost to
pests or weather. So even if you remove one-third of its leaves a
tree can gain ground. Thus the rule "Don't remove more than a third
of the foliage at one time."
The one-third rule is a good guide when you
want a plant to keep getting bigger but it can
be broken. We break it all the time when we
are Pruning to Keep a Tree
Small. Another
situation that may prompt us to break the rule
is when a young tree has a lot of clutter and
many badly placed limbs. Then, it's better to
cut away and "ask" the tree to produce new
limbs while it's young. It will be better
balanced sooner in terms of number and
spacing of main limbs.
Above: Adhering to the 1/3 rule. The branches we removed are
on the ground. The leaf buds on them add up to about half as many
as are left on the tree. The proportion may look more like
50-50 but that's because a number of the bud-dense upper branches
on the tree are nearly invisible in these photos because they have
dropped their leaves. 
Right, and above, left: Blue arrows mark the leafless top of
the tree.
Count leaves or
buds,
not length of limbs
Don't confuse bud/leaf count with amount of wood
removed. In training a young tree you will probably take out mostly
lower and inner branches, which tend to have fewer leaves per inch
than limbs higher in more sun. So you may remove more than one
third the total length of branches, yet the tree continues to grow
with gusto.
Right: Here's an example of a long length of wood removed
without removing as many buds as are then left on a similar length
of wood on the tree. The owner of this kousa dogwood (Cornus
kousa) asked if it would be okay to shorten the lower branches
that are interfering with the patio in the foreground. The plan is
to one day sit under the tree's branches.
We recommended removing the lowest main limbs (A; and
eventually those at the B level as well) rather than shortening
them. The canopy (C) is already developing well on higher
limbs that will serve the overall goal. That seems a major
reduction but the lower limbs are mostly wood, compared to the
higher limbs that are in more sun and more densely clothed in
buds.
The owner was then concerned about losing the plant's wide
vase shape. However, that won't happen. The tree might temporarily
seem narrow but it is the specie's natural habit to spread.
Side branches will grow out from the remaining limbs and the crown
will again be as wide, but higher.
Preserve the
branch collar as you prune
Leave the thickened base of the branch -- the collar (below).
It's from the collar that woundwood will develop to seal the
pruning cut.
Use the three-cut
method to first remove the weight of a large branch, avoiding
tears from the branch down into the trunk. Then saw the stub to
just outside the branch collar. 
No paint or dressing is necessary and can even be
detrimental. The tree will seal over a wound
better
on its own.
Sponsored by Judy and Dan Kurkowski
in memory of Daniel "DJ" Kurkowski who
lives on in this oak planted in his
honor.
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