Author: Dianne DeLongchamps
When should I mow my lawn for the last time this fall?
Stop mowing when your grass stops growing, not on a fixed date. CSU Extension says to keep mowing until the lawn stops growing. Along the Front Range, that usually lands sometime in October as the soil cools down. Once the grass has gone two weeks or more without needing a cut, you are close to done for the year.
Keep your mowing height the same for that last cut as it is all season. Luke and I recommend never mowing below 3 inches in Colorado. Kentucky bluegrass and fescue, which make up most of the turf in Northern Colorado, should not be cut low under any circumstance. CSU’s preferred range is 2 to 3.5 inches, so 3 inches sits at the high end of it.
Scalping a lawn low going into winter is a common piece of bad advice, and CSU Extension’s PlantTalk Colorado mowing guidelines push back on it directly, which we get into below. Fort Collins, Windsor, and Timnath all sit in roughly the same frost window, so this timing advice applies across our whole service area, even though any single yard can run a week or two ahead or behind depending on sun and soil. If you would like help with the parts of fall lawn care that are not mowing, Clean Air Lawn Care treats lawns in all three towns.
Why watching the grass beats picking a date
Every fall looks a little different along the Front Range. Some years bring an early cold snap in late September. Other years stay mild into November. Cool-season grasses like Kentucky bluegrass and tall fescue slow down as soil temperature drops, not on a set day on the calendar, so the grass itself is always a better guide than a date.
The Colorado Climate Center, based at Colorado State University, adds another reason to distrust an old calendar date. In its analysis of first fall freezes, it says Front Range and eastern plains locations have generally shifted one to two weeks later. It also says that even with an average shift toward later freezes, an extremely early cold front can still arrive, as one did in eastern Colorado in September 2020.
Don’t cut it shorter for the last mow
This is where a lot of bad advice floats around. Some guidance says to scalp your lawn low before winter to prevent snow mold. CSU Extension’s position is the opposite. The PlantTalk Colorado page says, “Scalping is never recommended, nor is there any reason to change mowing heights during the year.”
The same page explains the cost of cutting too low. Mowing grass to a height of less than 2 inches can reduce drought and heat tolerance, and it can cause a higher incidence of insect, disease, and weed problems. CSU also notes that grass plants undergo less stress when the amount of blade left on the plant can still function efficiently. A last cut at your normal height leaves the lawn with the most blade to work with as it goes into dormancy.
What first frost changes about mowing
Once Fort Collins gets its first light frost, usually sometime in early October, grass blades stop putting out new growth as quickly, even though the roots keep working underground for a while longer. Frosted grass blades are brittle, so wait for any frost to melt off before running a mower over them.
What happens if you mow a little too late
Not much. Mowing after growth has genuinely stopped for the season doesn’t hurt a dormant lawn. It’s just not doing anything at that point. The bigger risk is stopping too early, which lets grass get tall and floppy right as the first snow shows up.
How often you should mow as fall goes on
The general mowing rule is to never remove more than a third of the grass blade in a single cut. CSU’s PlantTalk page puts it the same way: mow often enough that no more than one-third of the blade is removed in a single mowing, which it says can range from four to 10 days between mowings. As fall goes on and growth slows, that gap naturally stretches out on its own. You don’t need a new schedule. Just keep following the same one-third rule and let the time between mows get longer as the grass tells you to.
The mowing interval also works as your growth meter. In the growing season, the one-third rule puts you on a four-to-10-day schedule because that is how fast the grass grows. When the grass has not grown enough to need a cut after 10 days, growth is slowing, and when two weeks pass without a cut, you are close to your last mow of the year.
Clean Air Lawn Care Northern Colorado is owned by Dianne, Paul, and Luke DeLongchamps — a family business serving Fort Collins, Windsor, and Timnath with organic lawn treatments and solar-powered electric equipment.
