The right mowing height for Ontario lawns
If you change one thing about how your lawn is maintained, change this. It costs nothing and it outperforms almost everything else.
Cutting height is the single most underrated variable in lawn care. It is free, it is instant, and in Ontario's climate it does more for turf health across a season than any product you can buy.
The number to aim for
Between 7.5 and 9 centimetres, or roughly three to three and a half inches, for the cool-season grasses that make up almost every lawn in the GTA. Most homeowners cut considerably shorter than that, often because a short lawn reads as tidy.
Why taller wins
A taller blade means a deeper root system, and a deeper root system means the plant reaches moisture that a shallow-rooted lawn cannot. That is the difference between a lawn that goes dormant in a July dry spell and one that holds colour.
Taller grass also shades its own soil. Cooler soil loses less water to evaporation and gives weed seeds a much harder time germinating, because most of the weeds that colonise an Ontario lawn need light at the soil surface to get started.
A thick, tall lawn is the cheapest weed control there is, and the only one that keeps working.
The one time to go shorter
The final cut of the season, in late October or November. Dropping the height slightly for that last pass reduces the amount of leaf matter that mats down under snow, which lowers the risk of snow mould appearing in spring.
One notch down is enough. This is not an invitation to scalp the lawn before winter.
Sharp blades matter as much as height
- A sharp blade slices the leaf cleanly and the wound closes quickly
- A dull blade tears it, leaving a ragged edge that browns within a day
- That browning is what makes a lawn look grey a day after mowing
- It is also an open door for disease
If your lawn looks slightly washed out the day after every cut, the height is probably fine and the blade is probably dull.