Pruning
for Strength
The
first guide to pruning a young shade tree is to have a clear understanding
about what pruning can do for the tree — and you. For example, we know to
prune modestly --if at all --when transplanting a new tree. An immediate
objective must be to strengthen and expand the root system which is usually
reduced by 80-90 percent during transplanting. To meet this objective, as
much as possible of the
leaf surface (the tree’s food factories) is left intact. Only damaged or dead
limbs should be removed.
After
the first year, pruning should begin in earnest. Pruning with strength as the
objective is the best way to avoid weak branches later on, and to prevent expensive
corrections that will otherwise become necessary.
What
to look for:
Branch
Angles and Size
Narrow
angles signals a point of future weakness, whether in the trunk or crown. The
reason is that as the two branches grow, neither has sufficient space to add
the wood needed for strength. Instead, they grow against each other. The effect
is similar to hammering in a wedge. To prevent this and the expensive problems
that are sure to follow, simply remove one of the two branches. For strength,
the ideal branching angle approximates 10 or 2 o’clock.
Lateral
branches should be no more than 1/2 to 3/4 the diameter of the trunk. As the
trunk grows it will strengthen the joint by adding wood around the branch —
like a dowel in a chair leg.
Watersprouts and Suckers
These
“parasite” sprouts can occur at the base or inside the crown. They are rapidly
growing, weakly attached, and upright. Usually they use more energy than they
return to the tree. It is best to remove them as soon as possible when it
is obvious they are vigorous sprouts.
Rubbing
Branches
Branches
that rub result in wounds, decay and notches. Remove one of the offending branches.
Center
of Gravity
Young
trees deformed by wind may be corrected by pruning. Move the tree’s center of
gravity to a point more central over the trunk by cutting back the leader and
laterals on the downwind side (or direction of lean) to more upright branches.
Temporary
Branches
Branches
below the lowest permanent branch can protect young bark from injury from the
sun and add taper and strength to the trunk. Particularly in lawn plantings
where lower limbs do not block passage or tempt vandals, the limbs may be left
for 3-4 years after planting. Then remove over the next 2-3 years, beginning
with the larger temporaries. Don’t let the temporary branches become large and
vigorous. Shorten the larger temporary branches, or remove vigorous temporaries
if less vigorous ones can be selected.
Caution: When
pruning diseased trees, dip your shears in household bleach before storing or
moving to the next tree. Be sure to rinse and wipe dry before storage.
