What is thatch and how does it impact my lawn?
Many times, after a tough winter with a lot of snow cover, lawns develop thatch problems. This article will answer questions on how thatch comes to be, how to prevent it and how to manage it once it has become a problem.
What is thatch?
Thatch is a layer of dead and living grass shoots, stems and roots that shows up between the soil and the grass blades in your lawn. Thatch build-up starts when the turf produces organic debris faster than it can be broken down.
The parts of the turf that are most resistant to decay (stems, crowns and roots) make up the bulk of thatch. It is important to note that grass clippings usually do not contribute to thatch build-up because soil microbes will easily break them down in the right turf conditions.
Having some thatch in your turf is actually good. Thatch helps with the resiliency and health of your lawn. It is a good protector, as it provides insulation against temperature extremes and variations in soil moisture. A good thatch layer is a half-inch thick or less.
Problems caused by thatch
Although some thatch is desirable in your lawn, too much can result in some serious problems. Thick thatch layers can cause extensive root damage. Because thatch heats up and dries out quickly, the roots risk becoming too dry.
Wet thatch holds too much water during rainy periods, resulting in root rot. Lawn mower blades can scalp areas of thick thatch. When the wheels of the mower sink into thatch, the height of the cut is lowered. Also, crowns of grass plants growing in thick thatch layers tend to be elevated above the soil, making them more susceptible to scalping.
Another concern of thatch build-up is that it could potentially harbor large populations of disease-causing organisms and insects. Continuous applications of pesticides over a two or three-year period can bind to the thatch, reducing their effectiveness and preventing their movement into the soil. Also, some insecticides reduce earthworm populations resulting in reduced thatch breakdown.
The effects of soil and grass type
Soil conditions also contribute to thatch build-up. Acid soils (pH 5.5 or lower) discourage thatch-decomposing organisms and microbes. Soils containing large amounts of clay or sand also contain low amounts of these microbes as do compacted soils and soils with poor structure.
Some grass types produce a lot of stems and consequently form more thatch than others. Some examples are Kentucky bluegrass, creeping red fescue and creeping bentgrass. Grass types that do not typically produce significant thatch build-up are perennial ryegrass and tall fescue.
A good way to manage thatch is to prevent build-up to begin with. Choose a grass seed or grass seed mix with perennial ryegrass or tall fescue in it. Take soil tests regularly to monitor nutrient and pH levels. If your soil pH is low, applying lime to your turf will raise soil pH levels and encourage thatch decomposition.
Perform core aeration as preventative maintenance every fall. This will help to correct compaction and improve air movement into the soil allowing increased microbe activity. Fertilizing is good for turf health but should be applied at the correct rate and volume to avoid build-up. Also, only apply pesticides and fungicides when there is an evident problem.
When thatch layers reach an inch or more, preventative measures will no longer be effective. The thatch must be physically removed. This can be done with a de-thatching machine or good old-fashioned hand raking.
De-thatching should be done during cooler seasons of the year – ideally in spring, but also in the fall. Never de-thatch when the turf is weak or damaged or under heat or drought stress.
If you are not sure if your lawn has too much thatch, consult your local lawn company for their professional opinion.