When I was a kid, ‘power raking’ just meant you were putting a little more muscle into the annual spring task. A good raking after the lawn has dried sufficiently always perks it up. How do we know if a few rounds with a leaf rake are sufficient, or if we’re supposed to call in the heavy duty power rakes? Power raking is sometimes called dethatching or vertical mowing.
It’s all about thatch. Thatch is the tightly interwoven layer of undecomposed dead grass between the green grass blades and the soil below. A proper amount of thatch is beneficial in conserving soil moisture and blocking weed growth. Thatch slowly decomposes, releasing nutrients into the soil below. But if thatch builds up faster than it’s breaking down, a too-thick layer can impede water and air penetration into the lawn, increasing chances of disease and insect problems.
A lawn’s thatch can be assessed by cutting a small vertical wedge from the lawn with a knife, showing the lawn’s vertical profile. One-half inch of thatch is considered good. If the thatch layer is thicker than 1/2 inch, then thorough raking is recommended. Small amounts of thatch can be removed by hand-raking. But if the thatch is thick and tightly interwoven, power raking does a better job.
Power raking should wait until the lawn has dried sufficiently in spring to avoid damage to early spring lawns. University of Minnesota and North Dakota State University recommend waiting until the lawn has ‘greened up’ before power raking, and possibly waiting until the lawn has been mowed several times. There’s more danger in too-early power raking, than in delaying, as moist lawns are tender in spring until grass begins some growth. September is also a good month to power rake.
Power raking brings up large amounts of ‘fluff’ which must be raked up and removed.
Another process is called core aeration, in which a machine cuts small plugs of soil and thatch that are brought to the lawn surface to increase air and water penetration, which is valuable if soil is heavy and lawns have become compacted. If thatch is the only problem, then power raking is sufficient.
Some lawns never need power raking. Other lawns benefit greatly. The measurement of the thatch layer is the key.