When to Prune Back Trees & Shrubs
The pruning of shrubs and trees is ideally done in the spring, not in the fall. Evergreen shrubs, such as azaleas, rhododendrons, yews, and hollies, continue to need their green leaves to conduct photosynthesis through the winter, so no green foliage should be removed before and during this time. Deciduous shrubs should also be pruned in the spring, simply because it is wise to wait until spring to remove any branches which may be damaged during winter. Summer is not a good time to heavily prune shrubs and trees for the reason that the majority of new growth on all trees and shrubs occurs during spring months, not during the summer.
The timing of pruning trees and shrubs also affects flowering of these plants, particularly those plants that flower only in the spring. Spring-only flowering shrubs and trees such as azaleas, rhododendrons, lilacs, and dogwoods should be pruned back as soon as all blooming ceases and no later than the middle of July. This is because these plants create their blooms starting in late July, August and September. Pruning after July risks removing flower wood already created during these months. Once created, these flowers will be lost for the following spring. However, shrubs and trees that bloom in the summer will only flower on new wood and blooming is not affected by pruning in any season.
“Ever-blooming” shrubs, such as roses, should be pruned well in early spring, and may be pruned lightly in the summer during the breaks in the blooming cycle. Roses bloom in cycles, up to about six cycles per growing season. These cycle breaks are resting periods when roses finish one cycle and use this break to produce new foliage, which will set blooms for the next cycle.