When Does Grass Stop Growing in the Fall?

Grass stops growing in the fall when daytime highs stay below 10°C (50°F). That's the rule from Iowa State University Extension for cool-season grass like Kentucky bluegrass, which is what most Canadian lawns are. In most of Canada, that happens sometime in October or November. The Prairies and the north stop first. Southern Ontario, like Windsor and Hamilton, keeps going the longest.

What temperature does grass stop growing?

The number to watch is the daytime high, not the overnight low. Iowa State says the leaves of cool-season grass stop growing once daytime highs are steadily below 10°C (50°F). One cold day doesn't do it. It has to stay that cool.

Grass doesn't stop on one day, though. It slows down for weeks first. The Guelph Turfgrass Institute at the University of Guelph says cool-season grass grows best between 15 and 24°C (60 to 75°F). Penn State Extension gives the same range for leaf growth.

So here's how a normal fall plays out:

• Highs of 15 to 24°C (60 to 75°F). Peak growth. Early fall often sits right here.
• Highs of 10 to 15°C (50 to 60°F). Growth slows. You mow less often.
• Highs steadily under 10°C (50°F). The leaves stop growing. Time to put the mower away.

Penn State also says leaf growth rises with longer days, as long as the temperature and moisture are right. Shorter fall days are one more reason your lawn slows down.

When does grass stop growing in Canada?

It depends a lot on where you live. Environment and Climate Change Canada keeps 30-year climate averages for each city. Here are the normal daily highs for fall, plus the average first frost:

City	Sept high	Oct high	Nov high	First fall frost	Usual stop
Windsor, ON	22.9°C	15.8°C	8.8°C	Oct 30	November
Hamilton, ON	21.2°C	14.1°C	7.5°C	Oct 14	November
Kelowna, BC	21.7°C	13.4°C	5.6°C	Sept 28	Late Oct to Nov
Lethbridge, AB	20.2°C	13.7°C	4.8°C	Sept 17	Late Oct to Nov
Moncton, NB	19.5°C	12.8°C	6.1°C	Oct 4	Late Oct to Nov
Sudbury, ON	18.1°C	10.3°C	2.6°C	Oct 1	October
Saskatoon, SK	18.3°C	10.2°C	-1.2°C	Sept 15	October

The "usual stop" column is our plain reading of those averages against the 10°C rule. It's a normal year, not a promise. A warm fall pushes it later. An early cold snap pulls it sooner.

Look at Sudbury and Saskatoon. Their average October high is right around 10°C. That means growth winds down during October in a normal year. In Windsor, the October high is still close to 16°C. That lawn keeps growing into November.

Want a local look? Our city pages for Hamilton and Saskatoon cover more about lawns in each place.

Does frost stop grass from growing?

Not by itself. Look at the table again. In every city, the average first frost comes before daytime highs drop under 10°C for good. Saskatoon's first frost is around September 15, but its average October high is still about 10°C.

A frosty morning can be followed by a sunny 14°C afternoon. The grass keeps growing on days like that. So don't park the mower after the first frost. Watch the daytime highs instead.

One tip: don't mow or walk on frosted grass. Wait until it thaws and dries off later in the day.

Do grass roots keep growing after the top stops?

Yes, and this is the part most people miss. Penn State says roots like cooler weather than leaves do. Roots grow best when the soil is 10 to 18°C (50 to 65°F).

Roots can still grow when the soil is colder than that. Penn State says they slow down sharply as the soil gets close to freezing, 0°C (32°F).

Penn State says fall is a busy time under the ground, too:

• Root growth is greatest in spring and fall.
• New shoots form most in early spring and fall.
• The grass stores the most food in the fall.

That stored food helps the lawn recover in spring. It's why you shouldn't let leaves pile up in October. Iowa State says a layer of leaves blocks the light, so the grass can't make and store food before winter.

Why does grass also slow down in summer?

Cool-season grass doesn't like real heat. Its best range tops out at 24°C (75°F). The Guelph Turfgrass Institute says these grasses can go dormant in hot summer weather if they don't get water.

Penn State says Kentucky bluegrass root growth drops a lot once the top inch of soil hits 32°C (90°F). That's why a lawn can look tired in August, then perk up in September. The cooler weather puts it back in its best range.

So a slow lawn in July isn't the same as a lawn that's done for the year. In summer, it's waiting out the heat. In late fall, it's shutting down for winter.

How do you tell your grass has stopped growing?

You don't need a thermometer. Try these simple checks:

• Check the forecast. Are the daytime highs staying under 10°C (50°F) for the next week or two?
• Walk the lawn a week after you mow. If it looks the same as the day you cut it, it's done.
• Look at the clippings. If the mower barely throws any grass, there's nothing left to cut.

Iowa State says to keep mowing until the grass stops growing in the fall. Once it stops, you can put the mower away for the winter. Our guide on when to stop mowing in Sudbury walks through this for one northern city.

How short should you cut grass before it stops?

Bring it down a little for the last few cuts. Iowa State suggests lowering the mowing height in mid to late September to 6 to 7.5 cm (2.5 to 3 inches). Never cut off more than one third of the blade at once.

Don't leave it long and floppy, either. The University of Saskatchewan says lawns left long and matted over winter can get snow mould. So can lawns with lots of leftover leaves. Its advice is to cut and rake the lawn before snow arrives.

Leaves are the other fall job. You can chop them up with the mower while the grass is still growing. Our post on mulching leaves with a lawn mower shows how. Not sure how often to mow before then? Read how often to mow your lawn in Canada.

One note on lawn problems: our partner crews don't spray, and we don't give advice on chemicals.

Can a crew handle the last cuts for you?

Yes. Fall mowing is tricky to time. The lawn slows down, the leaves pile up, and the days get short.

Golden Oak Lawn Care matches you with a vetted, insured local crew in your city. They do the work. We stand behind it with the Golden Oak Guarantee.

Your crew handles your lawn mowing right up to the last cut. Then they can do a fall cleanup to clear leaves and tidy the beds before the snow. You get the same crew every visit, and a photo after every cut.

We price every lawn by its size from satellite images, so no one has to come by. The price depends on lawn size, how often you want visits, slopes, gates and how many leaves you have. Book the season with the Worry-Free Lawn Season and your first cut is free.

Want it handled? Get your price in 60 minutes, or call 1-866-904-LAWN.

Grass Growth Questions

Sources: Iowa State when to stop mowing, Iowa State fall lawn care, Guelph Turfgrass Institute turfgrass facts, Penn State Extension cool-season turfgrass growth, University of Saskatchewan snow mould, Environment and Climate Change Canada climate normals 1981 to 2010.