If you surf the web for lawn-mowing advice, you’ve probably seen this: Make your last mow of the season low — cut your grass lower than normal before putting your mower away for the winter.
Hold on, experts say. Setting mowing height too low could easily damage your lawn. And depending on where you live and the type of grass you have, you may want to do the opposite, and mow higher late in your growing season.
“I can’t think of any time mowing low is a good idea, but I know some recommend it,” says Karl Danneberger, Ph.D., a professor at the Department of Horticulture and Crop Science at The Ohio State University in Columbus, Ohio. Danneberger says to stick with the guidelines for cool- and warm-season grasses when it comes to mower blade height, and there are a few recommendations that are applicable to most of the United States.
Damage From Cutting Too Short
- Any time you cut a lawn below its recommended height, you risk scalping it, cutting so deeply that you damage the part of the grass plant that produces blades — the crown.
- Cutting well below the ideal height also discourages grass plants from establishing a deep root system.
Why Grasses Differ in Recommended Mowing Height
Considerable research has gone into turfgrass varieties and their proper cutting height.
The names of the two major types of grasses — warm-season and cool-season — reflect the climates where they thrive. Warm-season grasses and cool-season grasses both perform photosynthesis — taking in carbon dioxide and exhaling oxygen as part of their growth process.
But researchers found they vary in how the grasses capture carbon dioxide. The cool-season grasses, including fine fescue, Kentucky bluegrass and perennial ryegrass, begin the photosynthetic process with a three-carbon compound, while the warm-season grasses begin with a four-carbon compound. That difference distinguishes grass varieties’ ideal growing conditions and their need for shade. That in turn helps determine their proper height and how high or how low they can be mowed.
In general, grass should be clipped every week during the growing season, and more often during periods when growth has accelerated. One well-established rule of thumb says you should mow frequently enough so you never remove more than one-third of the blade.
Mower height recommendations for major grass types include:
|Recommended Mowing Height by Grass Type|
|Grass species||Recommended mow height (inches)||Mow when it reaches this height (inches)|
|Annual ryegrass||1.5 - 2||2.25 - 3|
|Bermudagrass (seeded)||1 - 1.5||1.5 - 2.25|
|Buffalograss||1 - 2||1.5 - 3|
|Colonial bentgrass||0.5 - 1||0.75 - 1.5|
|Creeping bentgrass||0.5 inch or less||0.75 inch or less|
|Dichondra||0.5 - 0.75||0.75 - 1.125|
|Hard fescue||1.5 - 2.5||2.25 - 3.75|
|Hybrid Bermuda||0.5 - 1||0.75 - 1.5|
|Kikuyugrass||1 - 1.5||1.5 - 2.25|
|Perennial ryegrass||1.5 - 2.5||2.25 - 3.75|
|Red fescue||1.5 - 2.5||2.25 - 3.75|
|Tall fescue||1.5 - 3||2.5 - 4|
|Zoysiagrass||0.5 - 1||0.75 - 1.5|
|Sources: University of California-Davis Integrated Pest Management program, University of Georgia-Augusta Richmond County Extension|
“With cool-season turfgrasses like the bluegrasses, ryegrasses, and tall fescue, I recommend mowing at the same height (correct or desired height for the turfgrass species) that has been done through the summer and fall,” says Danneberger. “The key thing is to keep mowing until you no longer are taking off clippings.”
Danneberger practices what he preaches: “My lawn was mowed this past Saturday at the same mowing height, which happens to be the last mow.”
Warm-season grasses such as Zoysiagrass and St. Augustine typically need more sunlight than cool-season grasses. Bermudagrass is not shade-tolerant, so shorter mows could help by allowing more light between grass blades during growing seasons. However, Danneberger suggests mowing higher than the recommended height when you prepare for winter.
“On warm-season turfgrasses like Bermudagrass, I would begin to raise the mowing height up a little,” says Danneberger. “This would be especially important in the more northern region of its adaptation (ex.Tennessee, Kentucky) going into fall. A slightly higher height of cut will enhance the plant’s ability to tolerate winter injury a little better. Also scalping or mowing short going into winter may inhibit fall photosynthetic activity.”
But Not Too High
But Danneberger warns against mowing too high. That’s because winter lawn diseases such as microdochium patch (pink snow mold) thrive on long grass. It thrives in areas with extended periods of cool, wet weather. This disease loves thatch, and after the snow melts, appears as pinkish spots in the lawn.
Snow cover is not necessary for the grass to become infected with microdochium patch. The pathogen grows best in cool, moist periods of 32 to 46 degrees Fahrenheit.
The University of Minnesota Extension Service says homeowners should keep mowing grass at the proper mowing height until it stops growing. That’s usually around late fall. The service adds that leaving grass too high could encourage vole activity during the winter months. These furry pests, sometimes called meadow mice, leave tunnels in your lawn you won’t find until after the snow cover melts.
Put Proper Mowing Practices First
Good lawn care practices matter more, the experts say, than trying to get your grass height within a millimeter of some golf-course ideal.
- Keep a mowing frequency that never lets the grass get too tall. You want to hit that balance between encouraging root growth (good) and encouraging weed heads to seed (bad).
- Leave your grass clippings in the lawn as mulch. Mulching beats bagging because the cut grass blades return valuable nitrogen to the soil.
- Vary your mowing pattern. Grass leans in the direction of the mower, and eventually becomes uneven. Mowing in a different direction also prevents you from wearing ruts into the lawn. That’s a particular issue for heavy riding mowers.
- Sharpen mower blades regularly. Dull blades damage lawn grasses, as they pull and shred rather than cut.
- Water infrequently, but deeply to encourage a deep, vigorous root system.
So if it’s growing, keep on mowing — but in general, keep within the recommended range. Once the grass stops growing, winterize that lawn mower before turning your attention to the leaf blower or snow plow. Your lawn will high-five you with spring green.