It’s that time of year when many home lawns in our coastal area are looking pretty tough. Most have not been mowed for several months and our cool, wet, dark winter days have been ideal for moss invasion.
WSU’s standard recommendation for moss control this time of year has been an application of ferrous ammonium sulfate. The iron in this mixture kills the existing moss, turning it black. The ammonium sulfate fertilizer stimulates grass growth by providing nitrogen. Good turfgrass health, however, depends on more than just moss killer and fertilizer. Most lawns can use a good thatching. The question often arises: Just how much thatch is too much?
Different species of grass accumulate thatch at different rates. Perennial ryegrass is a low thatch producer; bluegrass and fine fescues form a dense thatch that is difficult to remove. A layer of thatch ranging from a one-half to three quarters of an inch is generally acceptable in most lawns, but anything greater can cause problems.
Once a thick thatch layer is formed it must be removed by vertical mowing. Use a machine that has rigid or flexible blades or tines (power rakes) that can cut into or pull turf out of the soil surface. You can rent a power rake, or you can hire a professional lawn service to do the job. Attachments to your lawn mower are not as effective as true vertical mowers. The best time to dethatch your lawn is now, which will allow the grass sufficient time to recover before the stress of summer heat. Thatching now will also remove the majority of moss that is present.
After dethatching, always fertilize with a 3-1-2 ratio fertilizer. Be sure to water the fertilizer in thoroughly. De-thatching without follow up fertilization results in increased weed encroachment and ugly turf. Once a thick layer has been removed, dethatching every year or every other year will ensure a healthy lawn that is easy to manage.
Dethatching is less disruptive and a lot less work if it is done regularly. People who dethatch only after a severe thatch layer builds up usually destroy their lawns.
Donald Tapio is a WSU Extension regional specialist emeritus. He may be reached at tapiod@wsu.edu.
