year
Ontario Lawn Care Calendar
The whole lawn year on one page for Zone 5b/6a: when to fertilize, overseed, aerate, and dethatch — and the mowing and watering habits that do more for an Ontario lawn than anything in a bag.
Month by month · Zone 5b/6a · pesticide-free by law · Easy — timing is the skill · A few weekends a year
THE YEAR Month by month
Written for Durham Region / east GTA timing. In a late spring, shift April jobs into May; the lawn reads the weather, not the calendar.
| Month | What to do |
|---|---|
| March | Stay off the lawn while it’s soft and thawing. Sharpen the mower blade and service the mower before the rush. |
| April | Rake out matted, snow-moulded patches once the ground firms up. Set the mower to 7.5–9 cm (3–3.5 in) from the first cut. Core-aerate compacted areas if the soil is workable. |
| May | Spring fertilizer once grass is growing steadily (late April–May). Overseed thin areas if you missed fall — spring seed needs faithful watering. Mow weekly; never cut more than a third of the blade. |
| June | Keep mowing high. Water deeply and infrequently — about 2.5 cm (1 in) a week including rain — or let the lawn go summer-dormant and brown; it will green up again in fall. |
| July | Heat and drought: raise the mower a notch, water early morning if you water at all. Watch for grub and chinch bug damage starting late July (see the grub guide). |
| August | The repair season opens late August: core-aerate, overseed, and topdress. This is the single best overseeding window of the year — warm soil, cool nights, fall rains coming. |
| September | Overseed by mid-September at the latest so seedlings establish before frost. Apply the year’s most important fertilizer in early-to-mid September. Keep new seed moist. |
| October | Keep mowing as long as it grows, dropping gradually to about 6 cm for the last cuts. A late-fall fertilizer (late October) is optional; rake leaves off the lawn so it isn’t smothered. |
| November | Final cut around 6 cm (2.5 in). Drain and store hoses, winterize the mower. Stay off frozen grass — footprints on frost kill crowns. |
| December–February | Off season. Keep salt-heavy snow piles off one spot where you can, and plan seed and soil orders for spring. |
THE HABITS The three habits that matter most
Ontario’s cosmetic pesticide ban (in force since 2009) means weed control here is cultural — a thick, tall lawn is the weed control. Everything below serves that one goal.
- Mow high: 7.5–9 cm (3–3.5 in)Tall grass shades the soil, which keeps weed seeds from germinating and keeps roots cool and deep. Scalping is the fastest way to invite crabgrass and clover into an Ontario lawn.
- Water deep, not oftenAbout 2.5 cm once a week in dry spells, early in the morning. Daily light sprinkling grows shallow roots and fungus. A tuna can on the lawn measures your sprinkler’s output.
- Feed twice, at the right timesOnce in spring (May) and once in early fall (September) covers most lawns. Fertilizer on frozen ground or before a downpour mostly feeds the storm drain — and phosphorus near waterways is a genuine problem in the Lake Ontario watershed.
- Overseed a little every fallA bag of seed spread every September keeps the lawn thickening faster than weeds, grubs, and life can thin it. Prevention is the legal — and effective — Ontario strategy.
WATCH OUT Common mistakes
- Fertilizing in the July heatFeeding a heat-stressed or dormant lawn burns it and wastes the fertilizer. The September feed does three times the work.
- Cutting short ‘so I can mow less often’You get the opposite: thin grass, weeds, and more mowing drama by August. High and often beats short and rare.
- Reaching for a weed sprayerCosmetic herbicides are banned for Ontario home lawns — the ‘weed & feed’ products sold elsewhere in North America aren’t sold or legal to use here. Dig isolated weeds, overseed the gaps, and use an iron-based spot treatment where a product is needed.
- Aerating or seeding into mudWorking wet clay soil compacts it further. Wait until it’s moist, not sticky.
Good to know
Grass seed choices matter in Ontario: a mix of Kentucky bluegrass, perennial ryegrass, and fine fescues suits Zone 5b/6a — bluegrass for density and self-repair, ryegrass for fast cover, fescues for shade and drought. ‘Low-maintenance’ and endophyte-enhanced fescue mixes also shrug off some insect damage. Whatever you buy, fresh seed germinates far better than the bag that’s been in the garage for three winters.