When to prune trees and shrubs? Wait till after the leaves fall.

Pruning too soon can harm your trees and shrubs.So, when it comes to fall pruning, procrastination is the way to go.

Take my neighbor. I saw him walking his dog last week on a perfect warm September morning. We chatted for a while, and as we parted, he asked, “Is this a good time for me to prune my trees? I want to do some gardening while the weather is mild.”

“Wait a bit,” I replied. Although pruning a little branch or two may be OK, bigger tasks like thinning the crown or cutting a big limb can wait.

Reasons to procrastinate

Why delay? Consider these points:

• In early fall, pruning wounds close more slowly and plants are more at risk for fungal diseases than at other times of year. For most trees, the best time for major pruning is late winter to early spring because wounds close faster.
• Pruning in late summer and early fall may also stimulate new growth, which has little time to harden before cold weather comes. The cold can harm this tender new growth, and the tree may need more pruning in spring to remove the damage.
• If you want to prune in fall, wait until trees drop their leaves and are dormant—usually October or November. After leaf drop, you can see the tree’s structure and identify disease and insect problems more easily. Dormancy (especially late winter to early spring) is also a good time to prune evergreens because vigorous spring growth will hide pruning wounds.
• If you want to transplant transplant a small tree the next spring, late fall (October/November) is a good time for root pruning. This pruning technique stimulates new root growth at the cuts and helps a newly transplanted tree get established in its new location.
• One exception to the no-fall-pruning advice is that you should remove dead, diseased, and damaged wood as soon as possible -- for tree health and your safety. Take proper safety precautions at all times. Hire a professional arborist to remove big limbs, high branches, and any other tree job that you’re not prepared to do.

When I saw my neighbor later that day, he was lounging on his porch. “I’m waiting to prune,” he said, waving at me.

Do you prune in fall?

What’s your experience with fall pruning?

Penelope O’Sullivan is one of nine garden writers who blog regularly at Diggin' It. She is the author of "The Homeowner’s Complete Tree & Shrub Handbook" and 11 more books on trees, shrubs, hedges, flowers, herbs, and garden design. She is a guest speaker on many gardening topics, has written and scouted for numerous magazines, and owns a garden design business in New Hampshire. Her latest book, “The Pruning Answer Book,” co-authored with Lewis Hill, will be published in March 2011. To read more by Penny, click here.