Last Cut Before Winter; How Low Should You Mow?
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Q. It's almost time to take the mower deck off the tractor and replace it with the plow, and I have a question that I don't believe you've addressed in your lawn care articles: Should I cut my lawn (predominately fescue with some greengrass) a little shorter than normal when I cut it for the last time? I typically cut my grass at 4 inches; should I cut it at, say, 2.75 or 3 inches for the last cut? The reason I ask is that the grass often continues to grow after the last cut, and may reach 5 to 7 inches in height before it stops. When this happens, the grass becomes matted down from the snow. Part of my concern is that it looks unkempt. I can live with that if the grass is healthy, but some areas look yellow and seem slower to green up in the spring. Thanks for any advice you can give; really enjoy listening to your show on WYSO out of Yellow Springs Ohio.
---Jim in Bethel Township (15 miles north of Dayton)
A. Thanks, Jim! Now, I read through the advice in several State Extension system Bulletins on late season lawn height, and at first glance they seemed to be all over the place. But on closer inspection, I noticed that most of the states that were advising a low cut for the last cut were also advising what I consider to be way too many feedings over the course of the season. Some were even suggesting a July feeding for cool-season lawns, which is death on a stick to the poor grass. The states that provided the best basic lawn care advice mostly advocated not changing the height.
But I think you need to cut lower.
Specifically, I think you should wiggle your cutting height down all year long, not just in the Fall. You say that you're cutting at four inches, but a three-inch cut is ideal for like fescue and Kentucky green. Having three inches of green allows the lawn to maximize its photosynthesis. Cut it lower than that and the grass begins to use up more nutrients to grow faster and regain that missing height—all at the expense of the underground root growth that keeps weeds at bay. And three inches is the perfect height for shading the soil surface from hot summer sun.
But, I hear you asking--wouldn't longer be even better?
No, because a three-inch cut is good at staying upright. Once it gets too tall, the grass begins to bend over, mat down and shade itself, which invites disease to move in, especially in a wet season. Or in your late-season case, when a heavy snow cover sits on the too-tall grass, and you get one of the two diseases collectively known as 'snow mold'. Lawns need good airflow, just like other plants.
And if you're following the one-third rule, your 'four inch grass' is actually around five and a half inches tall by the time you cut it. (The "one third rule" is lawn care 101: Never remove more than one-third of the total height in any one cutting. So if you suddenly awake after aliens have had you trapped in a time-warping alternate dimension (which happens to me all the time) and your lawn has gotten to be seven inches high, you should only cut one and a half to two inches off the top the first time around, wait several days to a week and then cut again. Don't shock the grass by cutting off too much at once.
Anyway, our favorite lawn care advisor, Iowa State Turfgrass Professor Nick Christians, warns against lowering the cutting height at any time of year—Spring or Fall. Always cut at three inches high and always observe the one-third rule. The answer to late fall growth, he says, is to keep cutting until the grass stops growing.
And you know how Nature likes to zing you with these things—if you go down to two and a half inches because you're sure that your grass is only going to grow another half inch, odds are that a hard winter will hit fast, with freezing cold temps but no snow; and now your too-low lawn is suffering frost damage and surface desiccation. (Cold weather without snow cover is the most stressful winter combination for plants.)
Safe Lawn advocate Paul Tukey, author of The Organic Lawn Care Manual, also agrees with keeping cool-season lawns cut at three inches going into winter. And he's a real voice of authority here, as he spent most of his life maintaining and researching lawns in New England—where there's a high risk of winter turf problems like our listener's 'snow mold'. He also notes that he's rarely seen the yellowing and matting that indicate snow mold on lawns that were fed organically. And Nick Christians warns that the problem is worst on lawns that are overfed in the fall, because it's harder for them to stop growing.
So the bottom line is to keep cutting until the grass stops growing. Either delay changing over to that plow, or get the tractor ready to push snow but arrange to have a nearby mower ready for a last-cut loan. And perhaps feed the lawn a bit more gently and/or earlier next Fall to slow down that late season growth a bit.