Over time you lawn can build up thatch, which is a layer of dead or decaying grass leaves, stems, and roots which exists underneath the green vegetation of your lawn. All thatch is not necessarily a bad thing and in fact small amounts (less than 1/2 inch) can be beneficial for your lawn. A good amount of thatch can increase your grass resiliency, improve tolerance against traffic, and insulate against drastic soil temperature changes. However when the thatch layer starts to exceed 1/2 inch, problems begin to occur like your grass actually growing into the thatch layer affecting it’s durability and hardiness. Additional problems such as localized dry spots, mower scalping, disease and even insect pests can become part of the picture.
Thatch build-up is more of a problem in your stoloniferous and rhizome producing warm-season grasses like bermuda and zoysia. Cool-season grasses, which grow in bunches using tillers, produce less amount of thatch.
Thatch can be removed by hand raking or more preferably using a power raking device. Hand raking can be extremely laborious and is only practical for small areas of grass. Power raking devices (or verticutters) use rigid wire tines or steel blades to lift thatch debris and small amounts of soil to the lawn surface. Power rakes can be rented or consult a lawn care service company for their hired service.
Thatch removal is a vigorous process and should only be done when at least 30 days of good growing conditions are anticipated following the process. After de-thatching warm-season grasses in the early summer, apply a pre-emergence herbicide to prevent the germination of crabgrass. For both cool-season and warm-season grasses, a well balanced grass fertilizer application (triple 15, triple 16, or triple 20) at a rate of 1.0 – 1.5 lbs nitrogen/1,000 square feet is highly recommended to encourage new growth.
Early and mid-summer de-thatching is best but can be done in the late spring as long as your lawn has been green for 2-3 weeks and night air temperatures are above 60 degrees F. DO NOT de-thatch in the fall as warm-season grasses are not growing in optimal conditions and a de-hatching session would cause severe injury. De-thatch zoysia grass during the mid-summer for best results. After finishing the process, collect thatch and debris by raking or mowing it up.
Tall fescue, fine fescue, and perennial ryegrass develop thatch slowly and are also slow to recover from a de-thatching treatment and should only be done in the early fall around mid September. NEVER during the summer. Attempt to time the de-thatching so that your lawn has plenty of time to recover under optimal growing conditions. Re-seeding is an option if damage to your grass is severe.
Kentucky bluegrass is a little more hardy and can handle a de-thatching in early spring but will still be much better off doing so in the early fall.