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With winter approaching, many are performing final yard cleanup and other outdoor duties before snow falls. Besides raking leaves, shutting down the sprinkling system, cutting back perennials, etc., many are also pruning trees and shrubs.
Unfortunately, many woody plants should not be pruned in the fall. This is especially true for shrubs. Prune hedges and summer blooming bushes (rose of Sharon, butterfly Bush, blue mist spirea and others) as the snow melts off in early spring. Hedges can additionally be trimmed until late summer to maintain their shape. Prune spring flowering shrubs (lilacs, snowball bush, spirea, forsythia and others) within a week of them being done blooming.
There is not an absolute rule for when to prune trees. Some should be pruned in the fall and others in the spring or summer. Below is a list of common landscape trees and when to prune them. The list is primarily taken from the American Horticultural Society's book of pruning and training woody plants:
Ash: From late autumn to midwinter when fully dormant. Crabapple: Autumn too early spring. Light pruning to remove water sprouts in the summer is acceptable.
Elm: Autumn too early spring
Flowering pear: After leaf drop in the autumn too early spring
Flowering plum: Midsummer.
Fruit producing pears and apples: February to early March before buds start to swell. Light pruning to remove water sprouts in the summer is acceptable.
Stone fruits (cherries, peaches, plums and apricots): In March before buds start to swell but the coldest winter temperatures are past. Light pruning to remove water sprouts in the summer is acceptable.
Hawthorne: Between autumn and early spring.
Honey locust: From late summer to midwinter. Horse Chestnut (Buckeye): After leaf drop in late autumn to midwinter.
Japanese flowering cherries (Kwanzan, Akebono, etc.): Immediately after flowering in the spring.
Japanese zelkova: Late winter.
Juniper and Arbor Vitae: Late spring or early summer. Trim when new growth is fully extended but not hardened. Do not remove more than one third of the new growth. Remove any branches at a branch intersection.
Magnolia: Early to mid-summer, after leaves of fully expanded.
Maple: In the winter when fully dormant.
Mountain ash: Autumn too early spring.
Oak: Winter to early spring
Pine, spruce, true cedar (Cedrus spp.) and fir: Late spring or early summer. Trim when new growth (candles) are fully extended but not hardened. Do not remove more than one third of the new growth. Remove any branches at a branch intersection.
Poplar (Cottonwood, Aspen): Late summer to early autumn. Excessively pruning older trees may make them more susceptible to internal rot and canker diseases.
Redbud: Early summer.
Sycamore: Autumn too early spring.
Walnut: Midsummer two before midwinter.
Willow: Autumn too early spring.
