Lawn care · Summer
The Right Mowing Height for a Durham Region Lawn
If you change one thing about how your lawn is cut, change the height. It costs nothing, takes ten seconds, and does more for a Durham lawn than any product you can buy.
This one is free and you can do it yourself this weekend. If you’d rather not, we’ll send you a number.
Green in summer. Clear in winter.
The short answer
Cut at 3 inches (about 7.5 cm) for most of the season, and raise to 3.5 inches (9 cm) through the July heat. Never remove more than one third of the blade in a single cut. That's the whole rule.
Why height matters more than anything else you do
Grass is the only plant most people own that they deliberately injure every seven days. How much you take off decides whether that injury is trivial or serious, and the plant responds to it in a way that's close to mechanical.
Root depth follows blade height. A grass plant maintains roughly as much root below ground as it has leaf above it. Cut at 3 inches and you get deep roots that can reach water in a dry August. Cut at 1.5 inches and you get a shallow root mat that dries out the moment the surface does. This is why the lawn cut short is always the first one on the street to go brown, and why its owner ends up watering twice as much for a worse result.
Height is shade, and shade is weed control. Crabgrass seed needs light on soil to germinate. Taller turf shades its own root zone, so the seed never gets the signal. This matters far more in Ontario than it does elsewhere, because since the province banned cosmetic pesticides in 2009 there's no legal spray to fall back on. Density and height are the weed program here. Everything else is cleanup.
Taller turf holds soil moisture. The canopy keeps sun off the ground and slows evaporation. In a July dry spell the difference between a 2-inch and a 3.5-inch lawn is measurable in days of green.
Height by season
What we set our decks to, month by month, and why.
| Period | Height | Reason |
|---|---|---|
| First cut, mid-April | 3 in / 7.5 cm | Preserve leaf area while the plant rebuilds roots |
| May to June | 3 in / 7.5 cm | Peak growth; steady weekly cutting keeps the one-third rule easy |
| July to mid-August | 3.5 in / 9 cm | Maximum shade and moisture retention through heat and dry spells |
| Late August to October | 3 in / 7.5 cm | Back to standard as growth and rainfall return |
| Final cut, November | 2.5 in / 6 cm | Shorter going into winter reduces snow mould risk under the pack |
The final cut is the only intentionally short cut of the year, and it's short, not scalped.
The one-third rule, and why weekly cutting exists
Never remove more than a third of the blade in one pass. From 3 inches, that means cutting when the lawn reaches about 4.5 inches, no taller.
Break the rule and the plant loses more leaf than it can support, dumps a matching amount of root, and browns out for a week or two while it recovers. Do it repeatedly and the lawn never builds the root depth it needs, which is how a lawn cut every third week ends up thin and weedy no matter how carefully each individual cut is done.
That's the real argument for weekly service, and it's worth being honest about: it isn't that your grass needs a professional. It's that in May and June, a Durham lawn grows fast enough that fortnightly cutting can't obey the one-third rule. The schedule is the point. Our weekly visit is built around it.
Three things that undo a correct height
A dull blade
A blunt blade tears the tip rather than slicing it. Torn tips brown off within 48 hours and give the whole lawn a grey cast that people wrongly blame on drought.
Sharpen every 20 to 25 hours of cutting. For a homeowner doing one lawn that's roughly twice a season; for us it's every couple of weeks.
Cutting the same direction every time
Wheels run the same lines and the grass learns to lie the same way, so it gets pressed flat rather than cut and the ruts compact.
Alternate the pattern each visit: one week lengthwise, next week across, then diagonal. It's also what produces the striping people like.
Cutting wet grass
Wet blades bend away from the cutter and spring back up uncut, so the finish looks ragged however slowly you go. The clippings clump and smother.
If it can't wait, raise the deck a notch and take a narrower pass. Better to cut slightly high than to cut wet at the right height.
On clippings: leave them
Mulched clippings return roughly 25 per cent of the lawn's annual nitrogen need for free, and they don't cause thatch; thatch comes from roots and stems, not leaf. The only cuts worth bagging in Durham are the first of the spring, and any cut where the grass has got away from you and the clippings would sit in rows.
Common questions
Won't a taller lawn look untidy?
A 3-inch lawn cut weekly with a sharp blade and a crisp edge looks better than a 2-inch lawn, not worse: it's denser, greener and more even. Most of what people read as 'tidy' is actually the edge and the line, not the height. That's why we trim and edge on every visit; it's the detail that does the work.
Is there any lawn that should be cut shorter?
Fine fescue used as an ornamental, and creeping bentgrass on a putting green. Neither is what's in front of your house in Durham. For a bluegrass and ryegrass home lawn on clay, 3 inches is correct and there's no real argument about it.
What about the strip along the driveway that always burns out?
That's heat radiating off the asphalt plus, in winter, salt spray, a near-universal complaint on the wide new driveways through north Oshawa and west Whitby. Keep that strip at the full 3.5 inches all season, water it a little longer than the rest, and flush it with a deep soaking in early spring to move winter salt down past the root zone.
How high do you cut for Northline members?
3 inches from mid-April, 3.5 through July, and 2.5 on the final November cut. Same standard on every property, every membership: height isn't something we charge extra for. See what each membership includes.
Three inches every week, and the driveway in January
Cut height is the cheapest thing you can get right, and the easiest to let slide in a July heat wave. Members never think about it: three inches from mid-April, three and a half through the heat, 2.5 on the final November cut, and the same membership that keeps the lawn at the right height in August is the one clearing the driveway before the 7 AM target in January.
Three inches all summer is a Gold membership doing its job: $189 a month plus HST, $213.57 on the card. Roughly 26 lawn visits between mid-April and mid-November, then unlimited clearing through the winter, on twelve equal payments that do not spike in January. You are never quoted per visit on either side of the year. Compare the three memberships, or tell us where you are and we'll price your property the same day, Monday to Saturday.
Keep reading
More property care tips
When to start cutting your lawn in Oshawa
The first cut is the one most homeowners get wrong. Soil temperature beats the calendar, and two weeks of patience buys you a better June.
Read the guide →Aeration and overseeding: Ontario's September window
There's one stretch of the year when aeration and new seed actually work in Durham. Miss it and you've spent the money for nothing.
Read the guide →The fall cleanup checklist for Durham homeowners
Nine jobs, in the order they should happen, with the two that matter far more than the rest, and the one everybody does too early.
Read the guide →Want this handled for you?
Every tip on this page is something we do for members every week, on schedule, in uniform, for one flat monthly payment. Tell us your address and we'll send a real number the same day, Monday to Saturday.
Green in summer. Clear in winter.