Although the instinct to prune is strong in fall, it pays to be selective in what you trim up and when.
Pruning shrubs late in the season will encourage new growth. This fresh growth is tender and will not have a chance to prepare itself for winter, a process called hardening off. Winter temperatures will damage new, non-hardened growth.
Fall-pruned evergreens, such as yews, junipers and boxwoods, may not have enough time to heal their wounds before winter sets in, which can cause injury.
Lilacs and other spring shrubs should not be pruned in fall.
© Jo Ellen Meyers Sharp
Pruning spring blooming shrubs, such as lilac, forsythia, many viburnums and hydrangeas this time of year means cutting off next year’s flowers. The best time to prune spring blooming shrubs is about four weeks after they bloom, so wait until spring.
Avoid cutting back lavender, Russian sage and other woody perennials now. Doing so may diminish their winter hardiness, especially in northern climates.
If roses need to have their canes cut back for winter protection, prune them after the plants have gone dormant. You can usually tell plants are dormant when they drop their leaves. Summer and fall blooming shrubs also can be tidied up once they have gone dormant. Examples of these shrubs include burning bush (Euonymous alata), smooth leaf hydrangea (H. arborescens), and PeeGee, or panicle hydrangea (H. paniculata).