Basics

• Organic matter such as grass stems and roots, both living and dead, makeup the layer of thatch which naturally develops in all lawns. The materials in thatch do not readily decompose, making this a potential problem in any lawn. Some thatch improves the wear and traffic resistance of grass but excessive amounts have negative effects.
  
  

Development

• Thatch develops at different speeds depending on certain factors affecting its decomposition. Dormancy, acidic soil and pesticide exposure decrease the decomposition rate and cause more thatch accumulation. The growth rate also affects thatch development, with more thatch occurring in fast-growing grass. Thatch develops faster in tall grass, compacted soil and when nitrogen is applied excessively to the lawn. Insecticides and fungicides affect the amount of organisms present in a lawn to break down thatch, so frequent use of these chemicals encourages a thick layer of thatch to develop.
  
  

Damage

• Excessive thatch encourages diseases and pests, giving them ample living area right in the lawn. Water and pesticides fail to reach deep when excessive thatch develops, resulting in weak root systems and increased levels of pest problems. It prolongs humid conditions near the roots and further encourages disease. Lawns harboring too much thatch look brown on the bottom or appear brown after mowing simply due to the fact that the thatch is more visible.
  
  

Treatment

• Cut plugs from the yard and examine them for brown material between the grass and soil levels. Thatch should not measure more than 1/2 inch thick. Power raking, vertical mowing and coring all work for thatch removal. De-thatch on an annual or bi-annual basis for best results. De-thatch during spring growth to allow ample recovery time. De-thatching some lawns in the fall works as well. Complete de-thatching prior to performing lawn improvement or maintenance such as reseeding or fertilizing.
  
  

Prevention

• Avoid future problems with thatch and excessive development by taking preventive steps. Avoid under- and over-fertilizing lawn to prevent excessive growth while still encouraging healthy grass growth. Mow regularly at a high level and remove grass clippings. Irrigate weekly to encourage deep root growth. Core grass annually, power rake every fall and avoid excessive pesticide use.