10 Often Asked Questions about Pruning
By Jan Cashman • Posted on February, 18th 2011
Jerry’s father used to say the time to prune is when your pruners are sharp. That old nurseryman’s adage holds true for minor pruning, but now, in late winter when fruit and shade trees and shrubs are dormant, is the best time to prune. (However, do not prune maples and birch trees now; their spring sap will “bleed” through the pruning wound.)
Prune trees and shrubs to remove dead, damaged, or diseased wood, reshape, and control the size of the plant. Homeowners ask many questions about pruning. I’ll try to answer some of them.
Is late winter a good time to prune Evergreens?
No, it is better to prune most conifers in June when this year’s growth is new. Be careful when you prune evergreens not to cut them back too far into old wood or regrowth will not occur. Mugho pines can be kept dense by clipping off part of the growth candles in June. Upright junipers and arborvitaes should be “given a haircut” every other year or so to keep them dense. Erect growing spruce, pines, and fir look most natural with little or no pruning.
What is the best way to prune Junipers that have become overgrown?
Reach down into the interior of the juniper and cut back major branches which are about as long as your arm. This allows light to penetrate to the interior so new growth originates there and creates a natural, informal appearance.
Should I remove Double Leaders in my trees?
Yes, leaving a single leader on young trees is preferable. Narrow-angled crotches are weak and apt to split where wide-angled branches are stronger and resistant to breakage.
How much of a tree do I dare prune at one time?
Remove no more than 25 to 30% of a tree’s branches when pruning.
Can pruning improve fruiting?
Yes, thinning the branches on a fruit tree allows for consistent, larger fruit. Also, pruning and thinning creates an open center that allows sunlight to enter so the fruit develops there and ripens. Old wood on a fruit tree can be removed so young vigorous fruit-bearing branches develop. Remove suckers that come up from the base of the tree and water sprouts (too-vigorous vertical shoots that emerge from a horizontal branch).
Why doesn’t my Lilac shrub flower?
Pruning the tips of the branches every year on a lilac will cut off next year’s flower buds. Wait to renewal prune until after your lilacs bloom so you don’t cut off flower buds, removing the oldest branches to allow new young growth to form. An old overgrown lilac can be cut off at the ground and allowed to start over, but then may not bloom for a few years. What holds true for lilacs does not hold true for all flowering shrubs. Flower buds on roses and potentillas are formed on new growth, so pruning will not discourage their flowering.
How can I reduce the size of a shrub that has gotten too big?
It is better to plant shrubs and trees that will not outgrow their space. But renewal pruning or removing entire older stems and branches can control their size. Or you can even cut shrubs off completely at ground level to rejuvenate them.
Is there a correct way to make pruning cuts?
Yes, recent research has shown the healing advantage of pruning branches exactly at the growth collar (a swelling of the union of the branch and the trunk). Do not leave a stub where decay, insects, and disease can enter. When shortening shoots, cut just above a growth bud facing outward from the tree or shrub. If you make cuts to an inward-turning bud, the new growth will eventually cross and rub other branches.
To avoid tearing the bark of a large branch, remove the branch with 3 cuts. Start out from the crotch at least 6 “ and make an undercut about halfway through the branch. Your second cut should fall the branch free of the trunk. The third cut removes the remaining stub with no injury to the trunk.
Should I use tree paint on wounds after pruning?
The latest thinking is that tree wound dressings are not needed on pruning cuts. Wounds will close by a natural callus with exposure to air.
How do I prune Apple Trees or Mountain Ash Trees with the disease fireblight?
To prevent the spread of fireblight on the infected tree and trees around it, prune out and destroy infected branches, being careful to sterilize clippers with bleach or rubbing alcohol between cuts to avoid spreading the disease. Prune branches at least 6 inches past the infected area. Overpruning an apple tree that does not have fireblight can produce succulent new growth and wounds that then provide a place for the fireblight bacteria to enter.
In February or March when it is above freezing outside, sharpen your pruners and prune your trees and shrubs if they need it. They’ll benefit.
Need more information?
See our follow-up article: 8 More Questions About Pruning Answered