The process of dethatching removes the layer of organic material known as “thatch” that builds up under grass over time, giving it a spongy feeling when walked upon.  A thin layer of thatch can be helpful to reduce weed establishment and drought stress, but more than 1/2″ of thatch can become harmful to your lawn.  Increased thatch makes it harder for nutrients and water to pass through and get into the root-zone, creating a stagnant environment for the roots. Reduced oxygen to roots can mean increased risk of fungal disease development while also providing increased habitat potential for pests.

A lawn that receives aeration on a regular basis will typically not need to be dethatched because that process removes thatch with each plug. However, site conditions are the ultimate deciding factor on how effective aeration can be for the lawn. Dethatching is best performed in the spring because the process opens up the lawn for more new growth.

See Also:

What is Aeration?