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Sunday, August 27, 2000 - Page updated at 12:00 AM

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THE PRACTICAL GARDENER

Thatching, aerating, reseeding: It's the busy season for lawn care

Special to The Seattle Times

Q: When can I reseed my lawn?

A: That's a good question for late August, because as the weather cools and rains return, lawn rejuvenation rises to the top of the gardening list. Many of us are currently looking at dormant, stressed lawns showing the effects of a long, warm summer. In September and October, do the tasks that keep lawns in good health, green and growing. The period between Sept. 15 and Oct. 15 provides weather that suits all steps in lawn installation and renovation, including reseeding.

After aerating, overseeding with a Northwest adapted lawn mixture such as a mixture of fine fescues (such as chewings, creeping red, and hard fescue) and perennial rye will help the lawn fill in and grow thickly. Perennial ryegrass is a good choice for areas that will get traffic, such as play areas. Be sure to water newly seeded areas if there's no rain; allowing the seedlings to dry out will kill the new shoots. The stronger the lawn grows, the better it will resist invasive weeds.

Renewal and renovation also may mean thatching to remove accumulated material at the surface of the ground around the crowns of the plants. (Thatch isn't the result of "grasscycling," which means returning clippings to the lawn.) Aerating, another renewal process, removes cores of soil and thatch, allowing better water penetration. Be sure to aerate after a few good rains have left the soil moist; otherwise, the cores won't hold together to be pulled out. If you plan to aerate or thatch, follow these procedures when reseeding to revive and fill in the lawn.

First, consider how the lawn serves in the landscape. If it's primarily a household play field (or like mine, a parking place for the hammock), maintenance can be basic but not meticulous. Perfection isn't required in a play area. The turf may gradually be invaded by some native grasses and weeds, be kept mowed and fertilized, but not coddled. If the lawn is in a "show" area, a more detailed maintenance standard may prevail.

Does your lawn have its best chance to grow well? There's a principle in landscaping called "Right Plant, Right Place." Some of the difficulties people have with lawns relate to where the turf is placed in the landscape. Problems arise as people cling to the hopeful optimism that a lawn will grow wherever it appeals to us, whether the area is soggy from rain, or shady from trees. But turf grasses have specific needs, just as rhododendrons and roses do.

Is the location sunny? Lawn should be planted where it gets at least six hours of light daily. Shaded lawns grow poorly and ultimately run to moss and other weeds. Grass was originally a prairie plant, accustomed to wide open spaces for light.

The maritime Pacific Northwest was, before contemporary humans began rearranging it, primarily a forested area. Grasses don't grow well inside forests.

So if the lawn is too shaded, and failing to thrive, you may want to consider replacing the shadiest parts this fall with locally adapted ground cover. Washington State University Cooperative Extension/King County distributes a useful list of these, published as Community Horticulture Fact Sheet No. 77, "Ground Covers for Washington." Send a stamped, self-addressed envelope requesting it to Bulletins, WSU Cooperative Extension, 500 S.W. Seventh St., Suite A200, Renton, WA 98055.

The soil beneath the lawn also contributes to its success or failure. Does it drain well? Recent soggy winters have given us a chance to observe drainage patterns. Some people have had low spots that filled with water and just didn't drain.

Lawns won't survive in soggy ground over the long term. If it's impractical to install drainage or regrade to correct existing poor drainage, remove lawn from that soggy spot.

For optimum health, turf requires good soil under its roots. One of the most common sources of lawn trouble is inadequate soil depth. For best growth, aim for at least 6 to 8 inches of well-drained soil, before the sod goes down or seeding is done.

Many people have the unfortunate situation of finding themselves with a lawn that looks fine at first but declines rapidly after a few months or years. This is often traceable to poor soil preparation. Even the best quality sod can't cope with bad soil. Sod is sometimes unrolled over 2 inches of mix, with hardpan beneath. If your lawn is persistently soggy, dies out in spots, or is hard to keep watered in summer, dig out a 1-foot-square section and check the soil quality under the roots.

The Practical Gardener is prepared by Mary Robson, area horticulture agent, Washington State University/King County Cooperative Extension.

Copyright (c) 2000 Seattle Times Company, All Rights Reserved.

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