CULTIVATING SUCCESS : The do’s and don’ts of dormant pruning
Many people prune their trees and shrubs to improve plant appearance, encourage flower and fruit development, and promote overall plant health.
But there is more than meets the eye when it comes to pruning.
Determining when to prune your plants depends on the type of tree or shrub. As a general rule of thumb, the late dormant season (late winter to early spring) is best for most pruning.
Pruning in late winter, just before spring growth starts, leaves fresh wounds exposed for only a short length of time before new growth begins the wound-sealing process.
Another advantage of dormant pruning is that it's easier to make pruning decisions without leaves obscuring plant branch structure.
Time pruning to avoid diseases, other problemsPruning at the proper time can avoid certain disease and physiological problems:
- Prune apple trees, including crabapples, mountain ash, hawthorns and shrub cotoneasters in late winter (February-early April).
Spring or summer pruning increases the chances for infection and spread of the bacterial disease fireblight.
Autumn or early winter pruning is more likely to result in drying and die-back at pruning sites.
- To avoid stem cankers, prune honeylocusts when they are still dormant in late winter.
If they must be pruned in summer, avoid rainy or humid weather conditions.
- Some trees have free-flowing sap that "bleeds" after late winter or early spring pruning. Though this bleeding causes little harm, it may still be a source of concern. Examples of these types of trees are all maples, including box elder, butternut, walnut, birch and its relatives, ironwood and blue beech.
To prevent bleeding, prune the following trees after their leaves are fully expanded in late spring or early summer.
Never remove more than 1/4 of the live foliage.
Prune these after bloomingTrees and shrubs that bloom early in the growing season on last year's growth should be pruned immediately after they finish blooming: apricot, azalea, chokeberry, chokecherry, clove currant, flowering plum, flowering cherry, forsythia, juneberry, lilac, magnolia, and early blooming spirea.
Prune these before new growthShrubs grown primarily for their foliage rather than showy flowers should be pruned in spring, before growth begins: alpine currant, barberry, buffaloberry, burning bush, dogwood, honeysuckle, ninebark, peashrub, purpleleaf sandcherry, smokebush, and sumac.
Shrubs that bloom on new growth may be pruned in spring before growth begins. Plants with marginally hardy stems such as clematis and shrub roses should be pruned back to live wood.
EvergreensSpruces, firs and douglas-firs don't grow continuously, but can be pruned any time because they have lateral (side) buds that will sprout if the terminal (tip) buds are removed. It's probably best to prune them in late winter, before growth begins. Some spring pruning, however, is not harmful.
Pines only put on a single flush of tip growth each spring and then stop growing. Prune before these new needles become mature. Pines do not have lateral buds, so removing terminal buds will take away new growing points for that branch. Eventually, this will leave dead stubs.
Pines seldom need pruning, but if you want to promote more dense growth, remove up to two-thirds of the length of newly expanded candles.
Tarah Young is the Hubbard County University of Minnesota Extension educator in agriculture, food and natural resources. If you have any questions about this topic or any others, contact her at 732-3391. If information about agriculture, gardening and natural resources interests you, consider signing up for the Hubbard County UMN Extension Agriculture, Gardening and Natural Resources E-newsletter at z.umn.edu/HCExtensionNewsletter.