Mow high for weed and grub control

Mow at the highest setting on your lawnmower to promote deep roots, avoid grub damage and crowd out weeds.

Smart Gardening LogoMichigan has a tradition of mowing lawns short. Perhaps it is because many people want their lawn to look like a golf course fairway. Unfortunately, this is not practical for the average homeowner because golf course fairways are mowed three times per week with a frequently-sharpened reel mower, and irrigated daily during the summer. Trying to mow your lawn at a height less than 3 inches is actually stressful to your lawn and may result in the need to apply more insecticide and herbicide.

Mowing height

Raising the mowing height makes a more dense turf that out-competes weeds. Photo by Rebecca Finneran, MSU Extension

What height do you mow at?

It’s easy to determine the true cutting height of your mower. Pull your mower onto your driveway or sidewalk and measure the distance from the cement surface to the bottom of the blade-protection covering that goes all the way around the path of the blades. Most lawn mowers have an adjustment that allows the mowing height to be set between 2 and 4 inches.

What mowing height is best for my lawn?

The highest setting on your mower! The top setting for most mowers gives a cutting height between 3.25 and 4 inches. This is best for your lawn, but at a setting of 4 inches you may sometimes see some “laying-over” of turf blades that some people find undesirable. For this reason, some people prefer to mow at 3 or 3.5 inches. For the healthiest and most sustainable approach, Michigan State University Extension says 3.5 to 4 inches is most desirable.

Lawn mowing height

Lawns mowed at 3.5 or 4 inches out-compete weeds, tolerate grubs and look just as good as lawns mowed at 2.5 inches.

Why is mowing high good for my lawn?

Mowing high provides five valuable services:

  • It makes scalping (turf damage from mowing too short) much less likely to happen.
  • It allows you to clip about 30 percent of the leaf blade each time you mow (the optimum proportion).
  • It promotes establishment of a larger root system, which is more drought tolerant.
  • It provides broadleaf weed and crabgrass control by shading the soil surface.
  • It establishes a grub-tolerant lawn because of the larger root mass.

The weed and grub control provided by mowing high means you can use less pesticide on your lawn. In fact, if you combine mowing high with modest applications of fertilizer (1 to 4 lbs N per year, depending on how green you want your lawn), and watering during dry periods, you may not need to use any pesticides – herbicide for weeds or insecticide for grubs – on your lawn. If you have not been mowing high and watering during dry periods, you may need to do this for at least one year to establish a healthy lawn before you stop using pesticides.

Dr. Smitley's work is funded in part by MSU's AgBioResearch.

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