University of Vermont Extension
Department of Plant and Soil Science
Winter News
Article
PRUNING DORMANT PLANTS
Dr. Leonard Perry, Extension Professor
University of Vermont
Eager to get back in the
garden? If you have trees and shrubs,
those "warmer" days of winter are a good time to prune many of them
while they are still dormant.
The rule of thumb is to prune those
woody landscape plants that bloom on current season's wood while dormant. Those that bloom on the previous season's
wood, prune after they bloom in late spring on early summer. Examples of those that you should prune after
bloom are lilacs, forsythia, rhododendrons, and early viburnums. Prune these right after they bloom, as they
will then start forming flower buds for the following year. This is one answer to a question I often get,
"Why didn't my shrubs bloom this year?" Pruning these during summer or fall will cut
off next year's flowers. I often see
this with forsythia, which grow rampant and gardeners "shape" during
the growing season. Of course broken branches can be pruned off now in winter.
So all the rest you can prune now
while still dormant and resting for winter.
Some of the common shrubs you prune while dormant include glossy abelia,
barberries, blue mist (Caryopteris), summersweet, smokebush, spirea,
cotoneasters, and late viburnums (such as blackhaw and American cranberry
bush). Depending on how high you want
these to grow, you can prune them back to as much as above the first pair of
buds above the soil.
A drastic version of cutting back
shrubs in winter is known as "renewal" pruning. This
involves cutting a
shrub back to about six inches above the ground, and only is suitable for some
plants. This is a good practice for these shrubs if
they didn't bloom as in the past, or look overgrown with weak and straggly
stems. Renewal pruning invigorates these
shrubs, as drastic as it sounds and looks.
Candidates for this include glossy abelia, barberry, blue mist,
forsythia, honeysuckle, ninebark, shrubby cinquefoil (Potentilla), hibiscus,
lilac, spirea, and weigela.
If you can't bear to cut these
shrubs totally back, or don't want the sight of an empty spot in the garden or
landscape while they regrow, cut back in stages over a three year period. With this plan, only cut back to the ground
about one third of the oldest stems each year.
Some rampant growers, such as forsythia and ninebark, you may want to
continue renewal pruning each year. Some
gardeners practice this regularly even with shrubs such as lilacs, in order to
keep them lower.
A variation of renewal pruning is
known as "coppicing". This
cutting to the ground during winter stimulates vigorous new growth each
year. In the case of shrubby dogwoods
and some shrub willows, it can stimulate more brilliant stem colors. The sacrifice, though, is cutting off flowers
and fruits. If you want these, then only
coppice every other year. If butterfly
bush survives in your area, this too can be coppiced. A favorite large tree to coppice is the
Princess tree (Paulownia), creating tall bushy plants with large leaves
each year.
A type of winter pruning of trees,
seen more in Europe than America,
is called "pollarding". This
involves cutting trees back to the same point each year to control growth and
shape. The result is a knobby fist where
shoots grow from each year, a rather odd appearance if you are not used to
this. Purple smokebush is one small tree
you might try this with. I have seen it
quite commonly on street
A group of trees generally not
pruned in winter are known as "bleeders". These should be pruned in summer
after they leaf out if possible. During
late winter and early spring the sap is rising, and will "bleed" from
open wounds. This does little harm to the
tree except perhaps providing a site for disease infection, even though we
equate this to our own bleeding. Maple
is the most common and famous in this group of trees, which also includes
birch, beech, oaks, lindens, and elms.
Trees that you should prune in
winter or late winter include apples, flowering crabapples, mountain ash,
hawthorn, and honey locust. These may
get bacterial and other diseases (stem canker in the case of the latter) if
pruned in summer.
Pruning in late winter is good in
the sense that diseases are not active then to invade the open wounds. When the plants resume growth in the spring
shortly after pruning, the wounds will heal rapidly. Pruning in winter, especially if severe
pruning, will stimulate the plant to replace leaves and shoots first, perhaps
at the expense of flowering, so is a fact to keep in mind if flowering is
important. Keep in mind too that a tree or shrub, even after pruning, will grow
back to its natural shape. If you want a
certain shape in the landscape, it is easier and saves much pruning to choose a
plant with that shape naturally.
There are many online resources and
books on pruning, including when and diagrams showing how, including The
Homeowner's Complete Tree and Shrub Handbook by Penelope O'Sullivan.
Return to Perry's Perennial
Pages, Articles 