Short answer: Stop mowing when the grass stops growing, which in Sault Ste. Marie is usually somewhere in the first two weeks of October. Take the final cut down to about 6.5 cm, roughly two and a half inches, and get the leaves off before the first lasting snow. Those two things do more for next spring than anything you can put on the lawn in the fall.
September is not the end of the growing season
Most people in the Soo park the mower far too early. They watch the lawn crawl through August, decide it is done, and put the gas can away. Then the weather turns and the lawn takes off again.
That turn happened this month. The first twelve days of September were hot and completely dry here, highs in the mid to high twenties with no measurable rain. Since the thirteenth the highs have dropped into the mid teens, overnight lows are down around five to ten degrees, and the rain has come back. Cool nights and moisture are exactly what cool-season grass has been waiting for. Bluegrass, fescue and ryegrass have two growth peaks a year, one in late spring and one right now, and the autumn one is when the plant does most of its root building for the following season.
So the lawn is about to grow faster than it has since June. It still needs cutting on a normal schedule through the end of September and into October, and a lawn left to run tall in that window is the one that causes the trouble described below.
How to tell the season is actually over
There is no calendar date. Growth is driven by soil temperature, and the soil holds warmth for weeks after the air has turned. Watch the lawn instead of the forecast:
- Growth between visits gets shorter and shorter, until two weeks produces less than one week used to.
- You have had several hard frosts, not just one cold night.
- The colour flattens to a duller green and stops rebounding after a cut.
- Fallen leaves are sitting on the lawn rather than being pushed up through by new growth.
When those line up, the lawn is done for the year. In most Sault seasons that is the first week or two of October. Some years it is later. Cutting a lawn that is no longer growing does nothing for it, and cutting a frozen or frost-covered lawn bruises the blades, so wait for the frost to lift before the last pass.
How short the last cut should be
Through July and August a Northern Ontario lawn should be carrying 7.5 to 9 cm of grass, because the height shades the soil and holds moisture. The final cut of the year comes down from there to about 6.5 cm, or two and a half inches.
Get there gradually. Drop the deck one notch over each of the last two or three cuts rather than taking the summer height off in one pass. The one-third rule still applies in October: remove no more than a third of the blade at a time. Cutting a 9 cm lawn to 6.5 cm in a single cut takes far more than a third and leaves the plant shocked going into winter, which is the opposite of what you are trying to do. Our guide to how often Northern Ontario lawns should be cut covers that rule in more detail.
Keep the blade sharp for the last cut as much as the first. A dull blade tears the tip instead of slicing it, and a torn tip is an open wound sitting under snow for five months.
Why the height matters once the snow arrives
Snow is not the enemy. A steady snow cover insulates the crowns of the grass from wind and deep cold, and the lawn under it comes through fine. What causes damage is what is lying on the grass when the snow arrives.
The one place snow cover does not protect is the strip where the lawn meets pavement, which takes de-icing salt and plow blades all winter instead. That damage is also prevented in October, and our guide to stopping salt and plow damage at the lawn edge covers how.
Grass left long mats down flat under the weight of the snow and stays damp and dark all winter. That is the condition snow mould needs, and snow mould is what produces those matted grey or pink circles that show up at melt in April, always on the same lawns year after year. University extension guidance on snow mould in home lawns is consistent on this point: prevention is nearly the whole of the control, and mowing at a reasonable height into late fall is a main part of it.
Cutting too short is the other failure. Scalping in October strips the leaf area that protects the crown and exposes the soil to freeze and thaw cycles. About 6.5 cm sits between the two problems. It is short enough not to mat, tall enough to protect.
Leaves matter more than the last cut
If you only do one thing in October, get the leaves off. A mat of wet leaves blocks light, traps moisture and smothers the grass underneath in exactly the same way overgrown turf does, only faster. Lawns that come out of winter with dead grey patches in the shape of last year's leaf piles are common here and completely avoidable.
A light scattering of leaves can be mulched into the lawn with the mower and will break down over winter. Once the leaves cover the grass, mulching stops working and they need to come off. For most West End properties with mature trees, that means at least one proper clearing after the trees have finished dropping. We quote that work as fall yard cleanup, and it is the one fall service worth booking before the rush.
Two other things worth doing while you are out there: keep salt off the edge where the lawn meets the driveway and sidewalk, because a salted edge shows as a dead brown strip in April, and mark the lawn edge with stakes before the first plow so the blade has something to steer by.
What we do for season customers
Our mowing season runs through to the first Saturday of October, and the final visit is cut to the end-of-season height rather than the summer height. It is included, not an extra. Customers on a season agreement do not need to call and ask when the last cut is, we bring the deck down over the closing visits and finish the property clean.
Fall cleanup is quoted separately because every yard drops a different amount, and you can see how that works on the fall cleanup page. Our per-cut prices by property size are published in full, the same as they are all season.
If you want a written quote for the rest of this season or for 2027, send us your address. We measure the property by satellite and normally reply by email within 24 to 48 hours.
Sources
- Ontario Ministry of Agriculture, Food and Rural Affairs: Integrated Pest Management for Turf, Publication 845
- Michigan State University Extension: Snow Mold Management in Home Lawns
- Michigan State University Extension: Fall Lawn Care Tips
- Cornell Integrated Pest Management: Mowing Your Lawn
- University of Maryland Extension: Maintaining an Established Lawn