Dethatching or Power Raking:                    

Thatch is a brown spongy organic layer just above the soil surface made of both dead and living grass roots. 

Improper lawn management practices contribute to thatch.  A thick thatch layer contributes poor lawn health in all seasons and slows nutrient uptake.  Grass clippings do not contribute to thatch build up. 

Performing a light, shallow power raking, will un-mat turf and allow air to the root zone.