Should We Trim Shrubs And Trees In Late Summer?

When does late summer end, and early fall begin? Maybe it’s a half-empty versus half-full debate. At some point yard and garden tasks make the switch. Fresh summer vegetables finish up, replaced by fall harvest of potatoes, squash, pumpkins and onions.

What about the overgrown lilac that we never quite got around to trimming earlier. Can it be pruned now? And the apple branch that’s hanging too low? Is it ok to get a jump on next spring and do some trimming now?

The answer’s easy: No. Pruning in late summer or fall isn’t recommended. Oh, it might not kill the shrub or tree, but then again it could. Before rolling the dice with a tree or shrub’s life, consider why fall pruning can cause damage:

  • Pruning stimulates new growth. That’s great in spring and early summer, but when pruning causes new, fresh, young, tender shoots to sprout in late summer, they don’t have enough time to grow, mature and toughen up before winter sets in. All this still-tender tip growth can be injured during winter. When next spring arrives, the plant might be covered with dead twigs around the outer perimeter.
  • Pruning wounds don’t heal as efficiently in late summer. Plant cell growth slows as nature readies trees and shrubs for winter. Cut surfaces don’t close and heal. Open wounds make branches more susceptible to winter injury. Late summer/fall pruning can cause branch dieback, which will be visible next spring as injured branches fail to leaf out.

So, when is the best time to prune? Most deciduous trees and shrubs are best pruned in early spring before buds “break” and before branches leaf out. Lilacs and other spring-blooming shrubs can wait until after flowering, but for a total rejuvenation of old, leggy lilacs or spireas, early spring is better, cutting back to 6 inches above ground level. They won’t bloom the same year, but skipping one season of flowers is a small price to pay for a well-branched, healthy shrub.

Evergreen trimming is best in May and June.

Give the pruning shears a rest until next spring. “Happy Gardening!”