This is my best advice on fall pruning for homeowners who finally have time to prune in August and September: Stop.
Don’t get carried away with late-summer and fall pruning.
Reasons not to prune in fall
One reason is that spring-flowering shrubs have already set their flower buds for next spring. If you prune those shrubs now, you cut off next spring's flower buds, which means you won't have any flowers.
So, avoid heavy pruning of forsythia, quince, heirloom and New Dawn roses, mophead and oak-leaf hydrangeas, witch hazel, dogwood, cherries and other ornamental and fruit trees, pieris, azalea and rhododendron, corylopsis, mahonia, magnolia, silverbell, fringe tree, lilac, bridal veil and other early blooming spirea varieties, early viburnum species, redbud, early clematis (especially montana varieties), kolkwitzia, and kerria.
Another reason not to prune in later summer or early fall is that heavy pruning can stimulate lush regrowth if the weather is warm. When that regrowth occurs near a killing frost, the new growth is killed, having not had time to harden off before cold weather.
This is costly to the plant. Better to wait until the plant is fully dormant, when the weather has turned cold, to prune trees and shrubs.
Pruning of evergreens can easily and safely be done around the December holidays to provide greens for decorating. Two birds, one stone.
When pruning roses, cut only long canes or stems that can whip around in hurricane or winter winds. Don’t cut them down below about two feet high.
Winter weather routinely damages rosebushes, and in the spring you will need to reprune heavily to get rid of dead wood and get them off to a good start. If you prune heavily in the fall, there will be no wiggle room to prune off winter-killed material.
Late fall and winter are wonderful times to prune. With the leaves gone, you can easily see structural problems. Remove broken and damaged branches. Branches that rub against one another should be examined. Usually only one needs removal or shortening.
Avoid tree topping
Don’t let anyone talk you into topping your trees. No reputable arborist would do the kind of pruning that causes excessive, weakly attached new growth at the cut ends. You'll end up with more of a problem than you started with.
If you think your tree needs "topping," responsible arborists can thin trees to reduce their overall volume and remove weak, diseased or damaged branches. That's good for the tree.
Before you pick up those hand pruners, loppers, saws, and other tools, get some good information on how to make good pruning cuts and how to cut limbs from trees. This is crucial information and has changed a lot in the past few years. Conventional wisdom about this is often incorrect and ends up damaging your tree. Techniques have been improved and are updated in good books.
Trees and shrubs are important living investments in your landscape. Do it right and save yourself a lot of work.
Donna Williamson blogs regularly at Diggin' It. She's a master gardener, garden designer, and garden coach. She has taught gardening and design classes at the State Arboretum of Virginia, Oatlands in Leesburg, and Shenandoah University. She’s also the founder and editor of Grandiflora Mid-Atlantic Gardening magazine, and the author of “The Virginia Gardener’s Companion: An Insider’s Guide to Low Maintenance Gardening in Virginia.” She lives in the Shenandoah Valley of Virginia. To read more by Donna here at Diggin' It, click here.