Power Raking is commonly used to remove excessive layers of thatch, but do so with caution. Deep power raking can cause excessive damage to a lawn and even remove large amounts of living grass. Frequent, shallow power raking may be more beneficial.
Core Cultivation/Aeration is the preferred method for managing thatch. Aeration involves using a machine with hollow tines that penetrate the lawn and remove soil cores. The benefits of core cultivation include relief of compaction, improved air movement into the soil, improved water infiltration and improved root growth. Additionally, the soil cores, if left on the surface, will mix with and help break down thatch. Make sure the ground is moist before aerating to ensure maximum depth penetration of the tines. Dragging the cores with a piece of chain-link fence helps break and mix them into the lawn. Soil cores can also be broken up with a rotary mower. Over time and with irrigation, the cores will wash into the lawn.
When to Aerate and How Often? Most home lawns should be core cultivated at least once each year. The best time of the year is either in the fall or the spring when soil temperatures are ideal for root growth. Fall is the preferred time since the aerification holes will not be exposed to excessively hot temperatures during the summer and any weed seeds that were exposed with the soil cores are less likely to compete with the grass. Do not core cultivate during the summer due to excessive heat and drying.
The University of Idaho publication, Thatch Prevention and Control in Home Lawns, contains additional information and can be downloaded in PDF format.