Hill Gardens of Maine - Pruning Spring-flowering Shrubs

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Pruning Spring-Flowering Shrubs
by Fred Davis, MG, Hill Gardens of Maine (To view other articles, click Archives)

EMAIL QUESTION: "I've heard what sounds like conflicting recommendations for pruning my lilacs, forsythias and spireas. Some say spring; others fall; still others have told me they don't need pruning. Who's right? Do you have any pruning suggestions?"

ANSWER: Spring-flowering shrubs which fall into this "special" pruning category include: lilac, magnolia, spirea, forsythia, beauty-bush, viburnum, weigela, flowering quince, flowering almond, deutzia, red-twig dogwood and quite a few others. Spring-flowering shrubs are normally pruned immediately after spring flowers fade and fall. Yes, all spring-flowering shrubs and small trees may be cut back or pruned at other times of the year but the following season's flowers will almost certainly be jeopardized - if not lost altogether. Consider that after flowering in the spring, these types spend the remainder of the growing season - until freeze-up - preparing for, and setting, next-season's flowers. Pruning during dormancy or in late summer means that already-prepared flower buds will go into the chipper/shredder, compost pile or trash. After-flowering trimming and thinning also allows sufficient time for re-growth to occur which should quickly cover any evidence of pruning.

It's best to lightly prune every year to maintain a suitable (or desired) shape, rather than putting off the job until every third or fourth year. Procrastination may find you faced with a tangled mass of extensive overgrowth when you finally get on the job. I frequently advise questioners to accomplish most of their annual pruning by cutting bouquets of flowers and enjoying them indoors. Of course, this kind of "pruning" doesn't leave much color in the garden. So...you have a personal choice to make. Later, just after remaining flowers have 'gone-by', a light trim will finish the job.

First, look for any dead, weakened or diseased stems or branches. Remove these back to healthy, live wood - all the way back to the ground, if necessary. I believe it's wise to keep the center, inner part of a shrub fairly open to allow for air circulation and prevent excessive shading. An exception would be the dense, spirea japonica, which should receive an annual "haircut" immediately after flowering to remove seed heads and produce a compact and neat appearance. Or, if desired, they can be left alone to become a more random, undisciplined form (another decision for you to make). Allowing seeds to fall may mean baby shrubs coming up all over the place. So, unless you want seedlings to share or sell, get at your trimming before seeds mature...and rake away all the trimmings.

I also like to remove lower, drooping branches which are outside the normal "character" of the plant. Make clean cuts one-quarter- to one-half-inch above a healthy, outward-facing bud, using very sharp shears or clippers. Simply "whacking" away with a pair of hedge clippers (unless it's a hedge, of course) ignores the cutting-just-above-a-bud rule and, while it certainly looks neat after new growth covers the shearing, down below the random cuts is a tangle of twiggy remains. I prefer to prune and trim with a little more control than that offered by hedge clippers.

Sometimes, heavy, "to-the-ground" pruning may result in some fairly aggressive re-growth - "suckers". You'll want to remove most of these, leaving just enough to replace died-out parts and restore an attractive shape.

A word of caution: lilacs and magnolias should never be pruned back too heavily all at once; forsythias and spirea (Bridal Wreath) can—and should—be dealt with much more vigorously.

Your local Cooperative Extension may have a free publication to give you more guidance in your annual pruning. Don't be afraid to ask...after all, your taxes are paying for it!

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