Thatch is the tan, dry looking, undecomposed layer of tangles that forms just above the soil surface of your lawn. Made up of grass stems, lateral shoots and roots, often bound up with dead leaf blades and other lawn debris, this layer protects roots from exposure to sunlight and keeps water in the soil from evaporating.

However, when thatch builds up to a thickness of 3/4" or more, it prevents water, oxygen, and fertilizer from reaching the soil. Rain will just run off an impenetrable thatch layer. Soil microorganisms can't work to decompose organic material, depriving the grass of nutrients. A thick thatch layer can harbor disease spores and harmful insects and makes the grass less resistant to heat, cold, and drought. Thatch prevents grass seed from sprouting and inhibits the spread of new grass plants by runners.

Thatch often occurs in lawns that are frequently treated with chemical fertilizers. Other causative factors include too much or too little water, soil pH below 6.0, poor drainage, and soil compaction. Thatch grows more commonly in certain grasses, such as bluegrass and zoysiagrass, than in others.

To find out if your lawn has thatch build-up, use a long knife or shovel to take out a section of turf several inches deep in two or three parts of the yard. If thatch is minimal (about 1/4" thick), don't worry about it. If it's thicker than 1/2", you'll need to remove the thatch to maintain the health of your lawn.

Use a dethatcher attachment for your mower or tiller to tear out the thatch as you move across the lawn. Afterwards, use a rake to collect the loosened thatch and compost it.

Dethatching can be done in fall or spring when the weather is favorable for lawn rejuvenation. Do it prior to fertilizing or seeding. You may need to use your dethatcher more than once to reduce thatch to an acceptable level. If you try to get it all up the first time, you'll leave extensive bare spots in your lawn where weeds can encroach if you don't immediately overseed the lawn. Once the thatch layer is significantly reduced, you may not have to dethatch again for two or three years.

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C.R.S., Inc. · Spokane, Washington · USA