WHAT CAUSES LAWN THATCH ACCUMULATION?
What is Thatch?
Lawn thatch is composed of a tightly intermingled layer of stems, leaves and grass roots, which accumulates between the vegetation and the soil. Too much thatch increases the turf's susceptibility to lawn diseases, reduces its tolerance to drought, cold, and heat stress; and hinders the movement of air, water, fertilizers, and nutrients into the soil. In severe cases roots of the grass will not grow into the soil but only take root in the thatch layer making the turf susceptible to drought and heat stress.
What Causes Thatch to Buildup?
Thatch will accumulate in a lawn if the production of dead material exceeds the ability of the microorganisms in the soil to break down the organic matter. Thatch build-up occurs in lawns that have "dead soils" and is caused by an absence of beneficial microbial activity. Thatch buildup happens if there is poor soil aeration and drainage, improper lawn watering practices (usually too much water or too frequent water), cold temperatures, the use of chemical pesticides, and the use of synthetic fertilizers.. When a lawn's thatch layer is greater than 3/4 of an inch thick it may need to be mechanically removed.
Note: 99%+ of lawns DO NOT need to have the thatch removed via power raking or vertical raking. Please contact your local lawn care expert before scheduling a power rake.
If a lawn is building thatch faster than the microbes can break it down, this indicates that the lawn is lacking beneficial microbes. The cure to a thatch problem is not physical removal of the thatch, but the true cure to this lawn care problem is to stop the improper cultural practice that is killing microbes in the soil.
More than 1/2 inch of thatch can be a
problem for the lawn.
Improper Lawn Care Cultural Practices That Kill Microbes
- Shallow or frequent lawn watering practices.
- Severe over watering of the lawn.
- Fertilizing the lawn with fast release nitrogen. Salt based nitrogen like synthetic fertilizer sources kill microbes in the soil.
- Mowing the lawn infrequently, where more than 1/3 of the blade of grass is removed.
- The use of lawn herbicides and lawn fungicides. Both of these have been proven to kill microbial activity.
- Failure to aerate the lawn.
Power raking is a tool that can be used as a last resort to manage a major thatch problem, but power raking is not the cure of the thatch problem.
Steps to Repair a Thatch Problem in a Lawn:
- Power Rake, but only if it is before the lawn has greened up in the spring.
- Double Aeration to bring air into the soil.
- Sprinkler Audit to fix any improper lawn watering practices.
- Stop all fast release nitrogen or synthetic fertilizer applications.
- Stop all lawn herbicide or lawn fungicide applications.
- Apply Synergy with Corn Gluten Meal to stimulate beneficial microbial activity.
- Apply Humate Soil Conditioner to stimulate beneficial microbial activity.
Thatch Explained Quickly:
- Some lawn thatch is good! ½ of an inch or less is a normal amount of thatch.
- Thatch buildup occurs when the microbes in the soil cannot break down the organic matter as fast as it accumulates. This typically only occurs when there is a lack of microbial activity in the soil.
- Excessive thatch is caused by the absence of beneficial microbial activity.
- Excessive thatch is often caused by improper watering practices; usually too much or too frequent of watering.
- If the thatch layer is greater than ¾ of an inch then power raking is a tool to use to help manage the thatch.
- Power raking should not be performed after the lawn greens up. Typically power raking is performed in early March.
- Fast release nitrogen sources (non-organic fertilizers) can stimulate thatch buildup.
- Aeration or double aeration is a good way to help prevent thatch buildup.
THATCH PREVENTATIVE PRACTICES
- Lawn Mowing - Never cut more than 1/3 of the blade of grass at one time. Mulching the grass clippings does not increase the tendency to build thatch. Change the mowing height to 2.5 inches in the spring and fall and increase the height to 3 inches or taller in the summer.
- Lawn Fertilizing - Fast release nitrogen lawn care applications will result in a decrease in thatch decomposition and an increase in thatch production rates. Always avoid high dosages of synthetic nitrogen sources like ammonium nitrate because they are salt based and kill beneficial microbes. Organic fertilizers stimulate beneficial microbial activity in the soil.
- Lawn Irrigation - Avoid light and frequent watering. Always irrigate the turf deeply and infrequently. This entices the roots of the grass to grow deep into the soil instead of the thatch layer. The lawn may look worse for a few weeks, but deep and infrequent watering will stimulate the roots to establish into the soil instead of the thatch.
- Lawn Pesticide - Pesticides negatively affect desirable microorganism and earthworm populations. Lawn care pesticides should be avoided unless absolutely necessary.