Heat, drought, and pest obstacles aside, landscape plants now have completed most of this season’s growth.
The result in some cases is a landscape that’s blown past ideal sizes and is now bordering on jungledom.
There’s still time to do something about most overgrown plants this year, but the clock is winding down.
Most pruning work is best done from spring into mid-summer, and in the case of fruit and shade trees, mid to late winter. We’re now approaching the end of that optimal time frame and heading into the worst time to prune most plants, early fall.
Early-fall pruning — up until leaves drop and plants go dormant — is bad timing for three reasons:
1.) It’s a time when woody plants are beginning to prepare for winter cold. This is when plants slow growth and start to “harden” their wood and buds for the coming cold.
Shearing, whacking, or otherwise removing wood interrupts that process, and in at least some species, diverts energy into healing and new growth.
If you encourage new growth by pruning in September or early October, those new shoots and buds will be more susceptible to winter damage and the erratic up-and-down temperature changes we’ve had all too often lately.
2.) For trees and shrubs that flower in spring (forsythia, azalea, lilac, etc.), fall pruning is a bad idea because you’ll cut off flower buds that already have formed for next year. That means fewer or maybe no flowers next spring.
3.) When you whack in early fall, plants usually aren’t going to regrow enough to hide the cuts. That’s especially true of evergreens. The result is plants that look butchered until the following spring when full growth mode kicks back in.
August often isn’t an ideal time for pruning trees, shrubs, and evergreens either. Plants can be heat- and water-stressed this time of year, making pruning cuts one more insult that piles onto the stress load.
But if you really need to cut, now is better than early fall. At least you can compensate by giving pruned plants a good soaking before and after.
Dead wood can be removed any time.
Cutting down and/or removing woody plants in August also is fine.
If you have some leeway, wait until later in fall when leaves drop and plants go dormant. At that point, there’s no concern with young new growth occurring that quickly gets zapped by freezing cold.
Shade and flowering ornamental trees also are a bit easier to prune then when bare since it’s easier to see the branch structure. Plus, it’s less messy without leaves to rake or dispose of afterward.
The exception to fall pruning is flowering trees and flowering shrubs that bloom in spring — ones that generally bloom before about mid-June. These form their flower buds the fall before and are best pruned immediately after they’re done blooming. Examples include forsythia, lilac, azalea, rhododendron, deutzia, mophead and oakleaf hydrangeas, weigela, dogwood, redbud, and magnolia.
Summer-blooming trees and shrubs, such as roses, caryopteris, beautyberry, rose-of-sharon, panicle hydrangeas, smooth hydrangeas, butterfly bush, and summersweet, are best pruned in the dormant season from late fall through the end of winter, just before new growth begins.
The best time to prune evergreens is between the end of winter and mid-August. They should be pruned lightly and regularly as needed to maintain ideal size, not left to get way too big and then cut back sharply into needleless wood.
While boxwoods, yews, hollies, and hemlocks are a few species that can recover from that kind of severe pruning, most evergreens won’t fill back when pruned back into bare wood.
Perennial flowers that are getting too big can be snipped strategically now and then dug and divided into smaller root pieces between Labor Day and mid-October. Complete or bigger foliage cutbacks can be done any time after fall’s first killing frost and when new growth takes place next spring.
Annual flowers and container plantings also can be snipped back now to neaten them and to control size conflicts.
More when-to-do-what tips are in George’s “Pennsylvania Month-by-Month Gardening” book.
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