Floppy perennials that hog too much space or smother their neighbors in August are far from my mind in May, when the garden seems short of foliage and full of promise.

But when an ungainly perennial in full bloom flops over, the only possible remedy is to try to prop up the branches of the offender without breaking them. Not easily done.

Think back to which plants flopped in your garden last year. For most kinds, right now is the perfect time to head off the problem before it happens again. Simply get out the shears and start cutting.

Many perennials that tend to flop can be cut back by about half in late May or early June to prevent the problem without sacrificing any blooms. Russian sage (Perovskia atriplicifolia), for example. Unless you're growing a short selection such as Peek-A-Blue, which stands only 2 feet tall in full bloom, Russian sage often hogs too much space. If you cut this year's growth back by half now, it won't happen.

Tall varieties of asters are also notorious floppers. Cutting back by half now works wonders for them, too. Frequent digging and dividing — as often as every spring for some vigorous varieties — also helps, not only with floppiness but also with preventing mildew.

By fall, a boltonia plant in full bloom sometimes falls over. Cutting back by half now can cure that problem, too.

Sedums such as Mr. Goodbud, Neon, T Rex and Xenox have strong stems not prone to flopping. The commonly grown Autumn Joy, on the other hand, is notorious for falling over when it's blooming. Newly divided plants are not likely to flop but in spring when other garden chores seem more pressing, I buy a little time by simply cutting my Autumn Joy plants back by half.

While there are compact goldenrods (Solidago hybrids) such as Golden Baby and Peter Pan sized just right for a small garden, some beautiful varieties crowd their neighbors by the time their autumn bloom season arrives. Again, the solution is cutting back by half now.

These days, many newer varieties of chrysanthemums are naturally low-growing. The floppiness of older varieties is best controlled by removing the plants' growing tips every couple of weeks fromMay to the Fourth of July. This pruning produces plants that are bushier and sturdier, with more blooms.

Not all perennials can be cut back without sacrificing blooms. A few to avoid pruning include queen-of-the-prairie (Filipendula rubra), goat's beard (Aruncus dioicus), and spiny bear's breeches (Acanthus spinosus). If in doubt, an excellent resource is Tracy DiSabato-Aust's "The Well-Tended Perennial Garden" (Timber Press, 2006, $34.95).

Contact the writer: www.midwestgardening.com

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