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Wednesday, July 21, 2004 - Page updated at 12:00 AM

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Plant Talk

Q&A: Solutions for over-bearing perennials

Special to The Seattle Times

Q: We have three Crambe cordifolia in our gardens, and they're HUGE. Do you have any idea how and when I might divide them?

A: Crambe cordifolia are perennials with a low-growing rosette of leaves that throw up a statuesque cloud of tiny, honey-scented white flowers in June. The foliage is as broad and crinkled as cabbage leaves, topped with flowers that look like the familiar florist's baby's breath on steroids. To prevent the plant from getting so large it topples over, it's best to divide C. cordifolia every couple of years in early spring when the foliage is 2-3 inches high. But beware — divided plants will grow even more vigorously so be prepared to allow even more space for your crambes.

Q: All I've read (and been told) so far, is that people who grow hollyhocks must be resigned to the fact that they will develop hollyhock blight. I never knew of this condition in our hollyhocks in Los Alamos. Perhaps the altitude (7,600 feet) and the semi-arid conditions were more favorable. So far, I've been told to just let mine grow for a couple of years, cut them down, and burn them. This defeats the whole purpose of growing perennials, if one must periodically destroy them and start over. Do you know of any reliable control for hollyhock blight, or of any resistant strains available on the market?

A: I've never been able to grow healthy hollyhocks two years in a row, but the last couple of drier summers I've seen plenty of healthy plants in other people's gardens. Hollyhock rust, caused by the fungus Puccinia malvacearum, is especially destructive in damp weather, which is no doubt why you grew healthy hollyhocks in dry New Mexico.

Hollyhock rust isn't pretty. Infection first occurs on the lower leaves and progresses upward through the entire plant. Yellowish orange spots on upper leaf surfaces and brown lesions on the stems are followed by brown pustules on the underside of infected leaves. Eventually, leaf spots brown and drop out, leaving holes. Severely infected leaves turn brown and dry.

It is worth trying to control rust with diligence and good garden hygiene. The fungus survives winter in leaves infected the previous year. In the spring, spores are rain splashed or wind blown to hollyhock leaves, starting new infections. So in autumn, be sure to remove every last bit of the hollyhock, and in spring start with healthy transplants or seeds. Grow hollyhocks in a sunny location, space them far apart so that air circulates freely around them, water and fertilize well. To prevent rust spores from being splashed from one plant to another, always water at the plant's roots, never by overhead sprinkler or hose. Check the leaves for any spots and remove infected leaves as they appear. During wet springs and summer, you might need to use a fungicide early in the season to protect the leaves.

Valerie Easton also writes about Plant Life in Sunday's Pacific Northwest Magazine. Write to her at P.O. Box 70, Seattle, WA 98111 or e-mail planttalk@seattletimes.com with your questions. Sorry, no personal replies.

Copyright © 2004 The Seattle Times Company

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