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Lawn Thatch: Causes, Solutions and What to Look For

Lawn Thatch: Causes, Solutions and What to Look For

Lawn thatch buildup is a common problem for both warm and cold season grasses, occurring when grass or turf produce organic debris faster than microorganisms in the soil can break it down. Thatch develops naturally in nearly all types of grasses, as a layer between the green vegetation and the soil surface, comprised of a loose mixture of living and dead shoots, roots and stems. There are benefits to maintaining a thin layer of thatch, however buildups may occur spring, summer and/or fall, which need to be addressed before it has damaging effects on an otherwise healthy lawn.

A thin layer of thatch naturally protects grass roots, particularly during periods of extreme heat and drought. It also provides a buffer from fluctuations in the soils’ moisture levels. However, excessive thatch, considered when the layer is thicker than ¾”, will prevent moisture, oxygen and nutrients from penetrating the soil and damaging the grass. Other problems associated with excessive thatch:

  • Newly sown seeds may root in thatch layer, not in the soil. Since thatch cannot provide the same insulation, these new grass shoots are more prone to drying out quickly and dying.
  • Heavily thatched lawns will dry out quickly, endangering the root systems and necessitating more frequent watering.
  • Wet thatch will hold excess water during rainy periods, resulting in less oxygen penetrating to nourish the roots.
  • Mower scalping may occur when lawn mower wheels sink into thatch, thus lowering the height of the cut.
  • Excess thatch will increase pest problems, harboring larger populations of disease carrying insects and organisms.
  • Insecticides and fungicides can get trapped in the thatch layer, preventing them from effectively penetrating the soil to do their job.

There are a few main reasons why excessive thatch build up will occur in certain types of grasses:

  • Certain species of grasses are more prone, (including cool season grasses Kentucky bluegrass, creeping red fescue and creeping bent grass) because of their higher production of stem tissue more resistant to decay.
  • Soils higher in acidity inhibit a healthy population of micro-organisms that decompose thatch. Additionally, compacted soils tend to have lower microbial activity.
  • Fungicide and Insecticide application: certain fungicides may promote thatch growth due to an increase in grass root production that outpaces decomposition; certain insecticides lead to thatch build-up due to their affect on the earthworm population, which is very important to microbial activity in the soil.
  • Aggressive fertilization, particularly with nitrogen-based fertilizers, may cause thatch accumulation by encouraging an increase in stem tissue production and soil acidity levels.

The best way to prevent excessive thatch in your lawn is to monitor and manage the thatch levels. Good preventative measures include: seeding the lawn with the proper grass for soil conditions, climate and traffic levels; regular core aeration; periodic soil acidity testing; and proper and controlled pesticide and fertilization use. Once thatch levels reach 1”, preventative measures will no longer be helpful, and physical removal is necessary.

The best time to de-thatch cool weather grass lawns is typically late summer to early fall. The process of de-thatching can be tough on grass, and should never be performed during high stress periods such as drought and extreme heat to reduce the change of injury. Thatching rakes are the best option for smaller areas of grass and turf, which effectively slice into lawn and bring up vast amounts of dead material. It is also important to rake in one direction to prevent damage to grass roots. Once the thatch layer is removed, the lawn can be cleaned with the back side of a metal leaf rake.

Once excessive thatch is identified, it is important to take action and consult lawn care experts if necessary. As with most other lawn care concerns, knowing what to look for and how to properly monitor will make all the difference.

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