University of Vermont Extension
Department of Plant and Soil Science
Spring News
Article
PRUNING
FRUIT TREES
Dr. Leonard
Perry, Extension Professor
University of Vermont
Especially for young trees
just planted last year, late winter and early spring is an essential time to
prune. As trees are dormant, not yet
growing, this is usually called "dormant pruning."
If you
remember nothing else, keep in mind the 2 C's and 3 D's. Remove any crossed and crowded branches, and
any dead, diseased, or damaged. Crossing
branches rub on each other, wounding bark and allowing diseases to enter. Crowded branches keep light from getting to
the inside, so you won't get as many leaves and fruit, and may get more
diseases instead. For older trees, the
adage is that a bird should be able to fly through the tree without
interference.
Dead branches
are obvious in the growing season, but this time of year with no leaves you'll
need to look for ones off-colored, often with shrunken (canker disease)
areas. When pruning damaged branches,
prune back to just above a bud, to a lower branch, or back to the trunk. Where older branches come off the trunk they
form a raised area or ridge of bark. Cut
back to, but not into, this bark ridge or "collar."
Another
important point with many fruit trees is the branch angle, as measured at the
base, from the trunk. Those mostly
horizontal, usually a bit under 90 degrees from the trunk (a right angle), are
the strongest and bear the most fruit.
Those upright, especially at an angle less than 45 degrees from the
trunk forming a V-shape, have what are called narrow crotches (where the branch meets the trunk).
These are are vigorous, produce less fruit, and are prone to breaking in
wind and winter ice. Branch angles even may vary among cultivars of a fruit
type, such as Delicious apples growing more upright, and Jonathan being more
spreading.
You
have a couple options for such branches, one being to prune them off at the
trunk. If the tree is young, and the
branches are where you'd like them, they can be "spread". If real young, only a few inches long, push
them downward using a clothespin clamped on the trunk. If they're a bit longer, even a year or two
old, hold them downward for a season with wood stakes (with a cut off nail on
each in), or by hanging weights (fishing weights for small branches, cement
weights the size of small drink cups for larger branches).
There
are three main pruning systems that are used for fruit trees-- the central
leader, modified leader, and open center or vase shape. The central leader is just that--one main
branch reaching upward, the tree forming a conical or Christmas-tree
shape. It is often used for upright
trees that don't get too tall like dwarf or even semi-dwarf apples, or European
pears and plums. If you don't mind
standard size fruit and nut trees reaching a full height, often 30 to 50 feet
(more for most nuts), then the central leader system is for you, or rather
them.
On the
other hand, if you want to keep upright trees such as many apples, upright sour
cherry cultivars, and European plums (some of the latter are hardy into USDA
zone 5) lower, then prune these to the modified leader. This is like a central leader early in life
then, when at the height you want, prune out the main leader and allow main
side branches ("scaffolds") to develop.
When
selecting which scaffolds to leave, they should be equally spaced around the
tree, none directly and closely above another.
For dwarf trees, as you measure up the trunk, scaffolds should be about
a foot apart, about two feet apart for standard trees, a distance in between
for semi-dwarfs.
For
some trees you may want to use a variation of the modified leader-- the
multiple leader system. It
is a cross between the modified and the central leader. Once the tree
is tall enough for you to manage or as you desire, prune out the
leader but allow several upright (not horizontal) branches to develop.
This is often used for European pears; in
case the fireblight disease attacks one or more leaders, there will be
others
left.
The
final system is the open center or vase-- descriptive of the shape. This is used for spreading trees such as
peaches (where they can be grown, most aren't hardy even into zone 5),
filberts, spreading sour cherry cultivars, and American plum hybrids and their
species. For an open center, to allow full light to enter the center,
don't let a central leader develop. From
an early age of the tree, prune to have 3 to 5 main scaffold branches. Then each year in late winter or early
spring, prune off any upright shoots in the center of the tree. Prune upright shoots farther out on the
scaffolds back to a bud pointing outward.
This will keep the tree growing more horizontal then vertical.
A
couple other rules are useful when pruning fruit trees. The more you cut off, the more growth this
stimulates. So if you want to slow down
growth on a vigorous tree, don't prune it as much. Pruning in summer can help this way too, as
pruning then results in less regrowth than dormant pruning. Just don't prune after midsummer, so any new
growth can harden by fall.
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