When the growing season draws to an end, knowing when to stop mowing your lawn doesn't include a one-size-fits-all answer. However, there are two factors to consider before storing your mower for winter; the weather and the type of grass growing in your yard.
The proper timing of your last fall mowing is just as important as cutting the grass at the right height. Following a few basic rules helps your lawn make it through the winter and start healthy regrowth in the spring.
Fall Mowing of Cool Season Grasses
If you live in the central and northern United States or southern Canada, your lawn most likely consists of cool season grasses such as Kentucky bluegrass, perennial ryegrass, and tall fescue. As the weather gets colder and soil temperatures drop to 45 degrees, the top growth of the grass gradually slows down. At the first killing frost, cool season grasses stop growing visibly. That’s your cue for the last mowing of the season. For cool season grasses, mow your lawn for the last time just before or right after the first killing frost.
There are, however, exceptions. Cool season grasses don’t go fully dormant and can continue to grow during the winter. Growth is merely suspended (slowed down) and the complex sugars they form during cold weather act as antifreeze. During mild winters with extended warm periods in areas with otherwise subzero winters, the grass might keep growing well into the fall and sometimes even into December, albeit at a much slower rate than during its peak growing season in the spring and fall. If this occurs continue to mow as needed regardless of the calendar date.
Cut the grass at the same height as during the rest of the year, at a mowing height of 2.5 to 3 inches. Or, if adjusting the mower is easy and quick, you can set the mowing height ¾ inch lower but no lower than a height of 2 inches.
Fall Mowing of Warm Season Grasses
In southern regions, the preferred grasses for lawns are warm season grasses such as Bermudagrass, Zoysia grass, and Bahia grass. Unlike cool season grasses, warm season grasses go dormant during the winter when soil temperatures remain consistently below 55 degrees Fahrenheit.
So when warm season grass has stopped growing in the fall, mow it one final time at a height of 1.5 to 2 inches. It is recommended to cut warm season grasses at the higher end of the spectrum in the fall to help them store more carbohydrates during the winter. This also reduces the risk of cold season lawn diseases such as large patch, a fungus that is most active in cool, wet weather.
Proper Mowing Height
Mowing the lawn at the correct height in the fall is just as important as during the rest of the year. The general rule of not cutting grass too short applies. Grass blades should never be cut below the level where they are green. This is where photosynthesis occurs and if you cut the lawn too low at your last fall mowing, it will take longer for to regrow in spring. This can lead to patchy, uneven growth, with empty spaces that will be quickly invaded by moss and weeds.
Longer grass blades also provide better protection during the winter months. Cutting too short in fall can expose roots to frost damage.
On the other hand, leaving grasses too tall over the winter also can have detrimental effects. Especially in areas with mild winters, tall grass blades trap moisture and can harbor fungi and other diseases.
In areas with cold winters, keeping the grass short discourages mice, voles, and other critters from making a home in your lawn, especially under a snow cover. They burrow in the grass, making unsightly ruts and holes that need to be filled and overseeded in the spring.
Cool and Warm Season Grasses. University of Nebraska Extension.