Q: With the summer heat, some of my plants are leggy or have dead stems. When should I cut them back?

Herbaceous Perennials

A: Many of your summer color plants and herbaceous perennials will send out new growth as regular rain and cooler temperatures come to the area. If there are dead stems on plants, cut them back now and continue to water regularly if rain is sporadic. For plants that are leggy, such as summer blooming salvias and others in the mint family like rosemary, you may want to wait and trim when the weather is not as hot. For other herbs, such as flowering and scented geraniums, you should wait until they start to put on new growth as the weather cools. If you cut these back in hot weather, they may die. On coneflowers, Echinacea hybrids, and other plants in the aster family, such as zinnias, dead flower heads may be trimmed regularly and they will send up a new show of blooms until winter arrives. Then, as the weather cools, leave some of the seed heads as food for migrating birds such as goldfinches.

 

The recommendation for pruning is do not cut more than one-third of the plant’s size, then water and lightly fertilize – a slow-release organic fertilizer will be gentle on the plant. However, don’t cut any fall-blooming plant; they are now ready to go into their flowering cycle. This should help you keep your garden looking good into the fall.

 

Suzzanne Chapman
Author: Suzzanne ChapmanEmail: This email address is being protected from spambots. You need JavaScript enabled to view it.
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Suzzanne Chapman is the botanical collections curator at Mercer Botanic Gardens and promotes organic gardening, growing native plants, and protecting the environment. Send your questions to This email address is being protected from spambots. You need JavaScript enabled to view it..