Crater Landscape Management




What is thatch?

Thatch is the layer of living and dead stems, roots, stolons, and rhizomes between the green blades of grass and the soil surface. A thin layer of thatch (less than 1/2 inch thick) can be beneficial to the lawn because it helps to limit weed germination, reduce water evaporation, and protect from frost damage. However, thick thatch layers can prevent water, air, and nutrients from penetrating the soil, causing reduced root growth and increased potential for drought stress. Thatch also favors fungal growth and can harbor insect pests. Some turfgrass species, such as tall fescue and perennial ryegrass, do not produce much thatch. Other turfgrass species, such as bermudagrass, bentgrass, and Kentucky bluegrass, have creeping growth habits and rapidly build thick thatch layers.


Extension Service Garden Hints

Oregon State University Extension

Dethatch your lawn this spring

CORVALLIS - By summer's end, does your lawn green on top, but brown underneath? When you mow it, does it look dead and scalped? Your lawn may have too much thatch.

If you didn't dethatch your lawn in the spring, then another good time to get this chore done is early fall if you live in western Oregon, according to Tom Cook, turf grass specialist with the Oregon State University Extension Service.

If you live east of the Cascades, wait until spring, just as the grass starts to green up, generally about April for most areas.

Thatch is a layer of living and dead grass stems and roots. It is the natural consequence of a healthy lawn, explained Cook. For best results, dethatch your lawn about every one to two years, in March or April or in the early fall. Bentgrass lawns, the most common type in the Willamette Valley, are best maintained with an annual dethatching.

Regular dethatching forces buds to grow near the base of the grass stems, preventing the grass plants from being dead underneath and only green on top. Thatching frees new grass shoots to grow in thick and lush.

The easiest, most economical way to dethatch is to rent a dethatcher. Two types are available - the flail-type and the solid knife-type. The solid knife-type is better for bentgrass lawns, but may not be as readily available for rental except in larger, metropolitan areas.

Small dethatchers, sold as lawn mower attachments, are also available, but Cook doesn't recommend those, because they put tremendous strain on the lawn mower engine.

The old-fashioned, elbow-grease method to dethatch is to use a thatching rake.

Once you have rented your dethatcher, set the blades high enough so they are about 1/8- to 1/4-inch above the ground when placed on a hard surface such as a sidewalk.

"You don't want to destroy your lawn in the process of dethatching," warned Cook.

Dethatching should not pulverize the soil surfaces. Adjust the blades to about a quarter-inch above a concrete surface. Make between one to five passes through your lawn, until most thatch is removed.

After dethatching, fertilize the lawn with a nitrogen fertilizer to stimulate regrowth.

Homeowners who dethatch their lawns every one to two years will end up with about one to three pick-up loads of thatch from an average-size lawn.

"Thatch is only a problem when homeowners wait too long to dethatch," said Cook. "Dethatching regularly is just a little more work than mowing a lawn. But if you wait for too many years, removing thatch becomes a long, agonizing process. It needn't be."

The thatch can be composted or used for mulch if it is herbicide-free. If you have used a weed killer or "weed and feed" treatment in the month before dethatching, then do not use the removed thatch to make compost or mulch.

Never use clippings or thatch debris for mulch or compost if you have used a weed killer containing clopyralid. Even after composting, clopyralid remains active and can injure your ornamental plants.

By: Carol Savonen
Source: Tom Cook

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