It’s usually not a good idea to prune trees or shrubs in the fall, for a couple of reasons. If you're confused by instructions to prune on new wood or old wood, or if you're just not sure when is the right time to prune trees, here's what you need to know.

It's usually not a good idea to prune trees in the fall. For one thing, you could trigger a flush of new growth that will not be hardy enough to withstand freezing weather soon to come. Photo credit: gettyimages

One reason not to prune trees in fall is that pruning can trigger a flush of new growth. If this occurs in the fall, the new growth may not have time to harden before freezing weather sets in, leading to damage.

Another reason to avoid fall pruning is if the tree or shrub in question flowers on “old wood.” This means that it has already set flower buds that will open next spring or summer—hence, flowering on "old wood." Pruning this type of tree or shrub in the fall would remove those buds and diminish next year’s flower display.

The Best Time to Prune Trees & Shrubs

For plants that flower in the spring on old wood, wait until right after their bloom to prune them. Here are a few of the plants in this category:

• Witch hazel
• Forsythia
• Andromeda, lily-of-the-valley bush (Pieris japonica)
• Flowering quince
• Japanese rose (Kerria japonica)
• Viburnums, such as Korean Spice

Witch hazels, particularly hybrid varieties such as 'Pallida', bloom on old wood.

For plants that flower on new wood, prune in late winter or very early spring before they bloom. Here are a few plants that bloom on new wood:

• Beautyberry (Callicarpa dichotoma)
• Bluebeard (Caryopteris)
• Bush cinquefoil (Potentilla fruticosa)
• Butterfly bush (Buddleia)
• Rose of Sharon (Hibiscus syriacus)