Prune Like a Pro



Cass Turnbull

Plant Amnesty


Pruning a tree or shrub incorrectly can make the plant less attractive
and endanger its health. In the case of trees, poor pruning can even
endanger your safety by weakening the tree. Yet many home owners and
professional gardeners don’t prune properly.

Most trees and shrubs are hardy enough to recover from pruning
mistakes, though it might take years. Seven of the most common
mistakes...

Mistake 1: Tree topping. Some home owners believe they can control the
height of trees by lopping off the tops, but height is largely under
genetic control, preordained from the time the tree takes root.
Cutting off the top will only compromise the tree’s appearance, health
and safety. After a tree is topped, decay can enter the major limbs.
Simultaneously, the tree speeds up its growth rate to compensate for
lost foliage, expending energy and weakening the tree. The new
branches that result tend to be weakly attached, making them a hazard
later, when they are large and heavy. The exceptions are fruit trees,
such as apple, pear and peach trees -- the height of these can be
controlled by topping.

Better: If a tree is too tall for its location, the only remedy is to
cut it down and plant one that won’t grow as high -- although you can
make a tree less imposing by trimming the leafy canopy or removing
some lower limbs.

Mistake 2: Cutting branches flush to a tree trunk. If you cut branches
flush to the trunk -- or flush to an intersecting branch -- decay
penetrates the trunk, reducing the life span of your tree. Leaving a
longish stub of the branch is just as bad, because decay and insects
will be able to get in once the stub rots. Applying pruning paint
won’t solve the problem -- research has shown that these coatings are
worthless.

Better: Remove a tree limb by cutting close to the trunk or parent
stem, but not flush to it. Leave the “collar” in place -- the
turtleneck-like bulge at the base of the branch.

Mistake 3: Pruning every shrub into a tidy round or rectangular shape.
A neat shrub might appeal to you, but it’s bad for many shrubs,
including conifers (such as junipers), deciduous flowering shrubs
(spirea) and broadleaf evergreens (rhododendrons). Shearing off
branches creates a dense, twiggy shell-like exterior that restricts
the amount of light reaching leaves and keeps air from circulating
inside the plant -- problems for shrub health. It also forces shrubs
to waste energy by regrowing branches you’ve cut. The replacement
branches are likely to be unattractive water sprouts (see “Trimming
water sprouts”).

Better: Prune selectively, trimming branches here and there for a
tidier, more elegant look. If you prefer a tightly trimmed look, use
the right plants, specifically those with small leaves, such as yew,
boxwood, privet, pyracantha, box honeysuckle, Japanese holly and
bougainvillea, which are hearty enough to stand up to pruning.

Mistake 4: Trimming water sprouts. Pruned plants sometimes develop
water sprouts -- ugly, twiggy upward growths from spots where branches
were cut. Cherry and crab-apple trees, magnolias, witch hazel, double-
file viburnum and purple-leafed plum are prone to water sprouts. Most
people remove these growths, only to find more appearing in their
place the next growing season.

Better: Water sprouts should be considered a sign that the plant has
been overpruned and needs more branches. When water sprouts appear,
the best option often is to allow them to grow and prune the plant
less in future years.

Mistake 5: Using hedge clippers. These clippers trim the surface of a
plant, which is appropriate only for hedges. Power hedge clippers, in
particular, should be used only on hedges because they can do a lot of
damage.

Better: Most trees and shrubs should be pruned so the cuts are hidden
inside the plant, where the branches fork off from other branches or
the trunk. Pruning tools include bypass hand pruners and a pruning
saw. Felco-2 bypass hand pruners (cost: $70) and the Felco-600 folding
pruning saw (cost: $31) are considered the industry standards.
Available from Amazon.com and gardening stores. www.felcousa.com

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Mistake 6: Cutting off branches that are too large. If the diameter of
a branch is more than half the diameter of the tree’s or shrub’s trunk
or stem, it is too large to be removed without significant risk to the
health of the plant. The plant will be unable to wall off the injury,
and decay will gain access.

Better: Don’t wait until a branch rubs against your roof or blocks
your driveway before cutting it off. If the branch is anywhere close
to half the diameter of the trunk or stem, remove it now before it
grows any larger.

Mistake 7: Heavy pruning during seasons of harsh weather. Heavy
pruning can put a lot of stress on a plant, as can the heat of summer
and the freezing cold of winter.

Better: Do major pruning during times of the year when temperature
extremes are unlikely in your region so that these combined stresses
don’t overwhelm the plant. Spring is usually the best time for heavy
pruning. (Moderate selective pruning is okay anytime of year.)
Generally, it’s best to prune flowering trees and shrubs soon after
they flower.


Bottom Line/Personal interviewed Cass Turnbull, a professional
gardener in Seattle and president of Plant Amnesty, a nonprofit
organization that encourages proper pruning techniques. She is author
of Cass Turnbull’s Guide to Pruning: What, When, Where & How to Prune
for a More Beautiful Garden

(Sasquatch). www.plantamnesty.org

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