CORVALLIS, Ore. – Dethatching home lawns may be the most overlooked landscaping chore that homeowners face every spring.
"Thatch, a layer of living and dead grass stems and roots, is the natural consequence of a healthy lawn," said Tom Cook, turf grass specialist with the Oregon State University Extension Service.
The right amount of thatch provides a softer surface for bare feet and makes the lawn more resilient to wear and tear. But with more than one-half to three-quarters of an inch of thatch, needed water, air and nutrients will not readily penetrate into soil below the lawn. An over-thatched lawn is too dense, usually green on top and brown and dead-looking underneath. When it is mowed, the brown layer is left, making the lawn look "scalped."
How do you tell if your lawn needs dethatching?
"If your lawn is soft or spongy, or you have dry spots despite regular watering, then it needs some work," explained Cook. "If only the very top part of the grass plant is green, and the rest is brown, or you scalp your lawn when you are mowing, then, you may want to dethatch.
"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."
For best results, dethatch your lawn about every one to two years, in March or April. 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.
In central and eastern Oregon, Cook recommends dethatching just as the grass starts to green up which is generally about April for most areas.
"When you dethatch more often, you don't generate this big load of debris," said Cook.
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, according to Cook. Small dethatchers, sold as lawn mower attachments, are also available, but Cook doesn't recommend those, he said. 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 don't hit the ground. "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.
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. 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 to make compost or mulch, he warned.
Cook has posted a photo-illustrated presentation online about thatch management and his research on the subject:
Download PowerPoint Presentation: Thatch Management
The OSU Extension Service offers several of Cook's publications on home lawn care either online or in print.
Online home lawn care publications.
To see and order printed versions, request Extension's printed catalog by calling 1-800-561-6719.