A. Answering this question requires an understanding of the differences between thatching and aerating. According to Tim Brennan of Brennan Landscaping in Wauwatosa, thatching is the term given to removing a built-up layer of organic debris, typically leaves and grass clippings, that mats between the soil and grass.
Some thatch can be beneficial.
An excessive thatch layer can become a breeding ground for insects and grass diseases. Removing excessive thatch is best done during the vigorous growing seasons of spring and early fall, and should be followed by a root-stimulating fertilizer and watering. For the turf blends in our climate, the best time to aerate is also during the spring and early fall, again followed by an application of a root-stimulating fertilizer and watering. As to which treatment should be done when, Brennan recommends aeration as part of regular lawn maintenance. Every other year is probably sufficient, but this will vary depending upon specific lawn conditions.