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Time of year (when to prune)
The best time to prune live branches may depend on the desired results. Growth is maximized and defects are easier to see on deciduous trees if live-branch pruning is done just before growth resumes in early spring. Pruning when trees are dormant can minimize the risk of pest problems associated with wounding and allows trees to take advantage of the full growing season to begin closing and compartmentalizing wounds. A few tree pathogens, such as the oak wilt fungus, may be spread if pruning wounds are made when the pathogen vectors are active. Susceptible trees should not be pruned during active transmission periods. Trees with Dutch elm disease should have symptomatic branches removed as soon as a branch shows flagging. Susceptible, uninfected elms should not be pruned during the growing season in regions where this disease is a problem.
Removal of dying, diseased, broken, or dead limbs can be accomplished at any time with little negative effect on the tree. Plant growth can be reduced if live-branch pruning takes place during or soon after the initial growth flush. This is when trees have just expended a great deal of stored energy to produce roots, foliage, and early shoot growth so pruning at this time is usually not recommended due to the potential stresses. Stressed trees should not be pruned at this time.
Flowering can be prevented or enhanced by pruning at the appropriate time of the year. To retain the most flowers on landscape trees that bloom on current season’s growth, such as crape-myrtle (Lagerstroemia spp.) or linden (Tilia spp.), these trees are pruned in winter, prior to leaf emergence, or in the summer just after bloom. Plants that bloom on last season’s wood, such as Prunus, should be pruned just after bloom in order to preserve the flower display. Fruit trees can be pruned during the dormant season to enhance structure and distribute fruiting wood, and they are pruned after bloom to thin fruit.
Certain species of trees, such as maples (Acer spp.) and birches (Betula spp.), drip sap when pruned in the early spring when sap flow is heavy (see table below). Although unattractive, sap drainage has little negative effect on tree growth. Some of the sap dripping can be avoided by pruning in summer or at other times of the year.
Trees that drip sap when pruned in late winter/early spring.
| Avocado Birch Cottonwood Elm Flowering dogwood |
Hackberry |
Poplar |
