Fix Lawn Spots - Problem: Thatch

By the DIY experts of The Family Handyman Magazine

An ounce of prevention

1. Mow often and cut no more than one-third of the grass height.

2. Water your lawn less often but for longer periods to prevent shallow root systems.

3. Reduce the amount of fertilizer you spread at any one time.

4. Reduce the use of pesticides. This will help keep the worm and microorganism populations healthy.

5. Aerate at least once every year if your lawn is prone to thatch.

Photo 1: Check the turf
Slice the turf grass with a shovel and pry it back.
If the thatch depth measures more than 3/4 in., aerate at least 3 in. deep.

Photo 2: Aerate
Make two or three passes with an aerator until you've made 3-in.-deep holes 2 in. apart throughout your yard.

Photo 3: Rake in topsoil
Spread 1/4 in. of topsoil on the yard's most thatchy areas and then rake vigorously to fill the holes with loose soil.

Symptoms: If your grass feels soft and spongy when you walk on it, your lawn may have a thatch buildup. Thatch is a fibrous mat of dead stalks and roots that settles between the lawn's green leaves and the soil (photo above). When this mat becomes greater than 3/4 in. thick, it can cause your lawn to suffer from heat and drought. Affected lawns will rapidly wilt and turn blue-green, indicating they're hot and dry.

Cause: Cutting off too much at each mowing (letting the grass get too long) and cutting too low. Both will produce more dead grass tissue than microbes and earthworms can recycle. Thatch can develop in any soil but is most often associated with high clay content. Other causes are overfertilization and frequent, light watering, which encourage a shallow root system.

Remedy: Slice open a section of your lawn (Photo 1). If your grass shows 3/4 in. or more of thatch, it's time to rent an aerator. An aerator is a heavy machine that opens the soil by pulling up finger-size soil cores. The lawn will absorb more oxygen and water, which will encourage healthy microbe growth and give worms wiggle room.

Aerate in the spring or fall when the grass is growing but the weather is not too hot to stress the plants (Photo 2). If the machine isn't pulling plugs, your lawn may be too dry. To avoid this problem, water thoroughly the day before you aerate. You can also rake in topsoil (Photo 3) to increase the healthy microorganisms that aid thatch's natural decomposition. Topsoil is available at any garden center.

Recovery time: You can expect the thatch layer to decrease by about 1/4 in. per year, about the same rate at which it forms.

Renting a Lawn Aerator

If your goal is to have one of the nicest lawns on the block, you can go a long way toward achieving it with annual aeration.

When a lawn lacks sufficient air (a “compacted” condition), it grows slowly and becomes vulnerable to disease, insects and heat damage. The soil will become impermeable and shed water instead of absorbing it.

Gas-powered aerators are available at most tool rental stores. They're slow-moving but powerful machines, so ask the clerk for handling directions. An aerator weighs about 200 lbs., so be prepared for some heavy lifting or ask your rental store for a ramp to get it into a truck bed or van.

Cool-season grasses should be aerated in the late summer or early fall. Spring is best for warm-season types. (If you're not sure what type you have, take a sample to an expert at a local garden center.)

Resist the temptation to remove the thatch with a rented power rake. Power raking is less effective than aerating because it typically removes less than 15 percent of thatch and may damage the healthy grass as well.

CAUTION!

Call your local utility provider or 811 to mark your underground utility lines before you dig.