Friday, July 19, 1996 - Page updated at 12:00 AM

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Practical Gardener

Casoron Won't Kill Weeds That Are Already Established

WSU/King County Cooperative Extension

Q: After putting Casoron on a flower bed to kill weeds, how long before you can plant and grow anything again?

A: The product you refer to is one brand name for a pre-emergent herbicide, meaning it kills seedlings just as they germinate or prevents germination. Its chemical name is dichlobenil and it is sold under several names.

It's important to understand how this product works. It won't kill established weeds that are already up and flourishing. Because of its action, dichlobenil must be placed around established woody plants such as shrubs. The most appropriate use for it is during the late winter, over shrub areas after all weeds have been removed. It should be mulched over to keep the product working well. Also, do not over-apply it. Research in Oregon has shown that the product can have some residual action from year to year, and it's easy to over-apply by getting in the habit of using it yearly.

Dichlobenil isn't a good choice where bulbs will be planted, where new plants will be installed, in vegetable gardens (not registered for this use) or over perennial flowers. Like all herbicides, its job is to kill or inhibit plant growth, and it must be used properly. Do not use it on any plants that have been in the ground less than six months to a year - which eliminates the annual vegetables and flowers. It's toxic to germinating seeds and damages new root hairs on plants.

Hand-weeding and using a mulch over the area to prevent re-growth of weeds is a better strategy where replanting is desired. If weeds must be treated with herbicide, the chemical glyphosate (sold as Round-up and a number of different names) can be used on weeds that are actively growing. Re-planting can occur within four weeks after weed death. Glyphosate does not work on weeds that aren't in active growth. It wouldn't work, for instance, on the brown crisp weeds in a parking strip.

Q: Are any fuchsias good for growing outside pots, or are they all going to freeze in winter?

A: Explore gardens through September for hardy fuchsias, one of the great - and not used often enough - shrubs for the maritime Northwest. These plants go into the ground in spring and establish woody frameworks, then last through winter and come up the following year.

One of the best, and a plant that seems to need no particular care or fussing, is Fuchsia magellanica, with graceful branches that can grow to more than 5 feet. It has red and purple typical fuchsia flowers in late summer. Others that bloom well are "The President," Fuchsia magellanica "Alba" and "Santa Claus." Santa is just as red and white as you'd expect from the name.

To see hardy fuchsias displayed, watch for late August flower shows. The Seattle Flower Show, usually the last weekend in August at Northgate, has a comprehensive and fascinating fuchsia display sponsored by the Greater Seattle Fuchsia Society. The Bellevue Botanical Garden also has a fuchsia display, as does the Carl English Garden at Hiram Chittenden Locks in Seattle.

------------------------------------------------------------------ Gardening runs Friday in Scene and Sunday in Home/Real Estate. It is prepared by Mary Robson, area horticulture agent; Holly Kennell, Washington State University/King County Cooperative Extension agent, Susan Miller, integrated-pest-management specialist, and volunteer Master Gardeners. ------------------------------------------------------------------

Copyright (c) 1996 Seattle Times Company, All Rights Reserved.


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