When to Plant Grass Seed in Ontario
Fall seeding dates from Windsor to Thunder Bay, and why the same calendar date is fine in Toronto and too late in Sudbury.
When to plant grass seed in Ontario is late summer to early fall for most lawns. In southern Ontario that means late August to mid-September. In Ottawa, Barrie and the north the deadline comes in August.
Ontario spans more than a month of fall. The first frost in Windsor and Toronto arrives about six weeks after Sudbury’s, so a September seeding that works on the lakeshore is a gamble up north.
Ontario grass seeding at a glance: seed in late summer to early fall. Toronto: by about Sep 20; Windsor and Hamilton a few days earlier. Ottawa and Kingston: by late August. Barrie, Sudbury and Thunder Bay: by early to mid-August. Missed it? Wait for spring, once the soil is above 10°C.
Seeding somewhere else in Canada? See When to Plant Grass Seed in Canada for every region in one table.
Ontario Grass Seeding Dates by City
| City | Zone | Avg last spring frost | Avg first fall frost | Fall: seed by |
|---|---|---|---|---|
| Windsor | 7a | Apr 20 | Oct 28 | Sep 16 |
| Toronto | 6b | Apr 20 | Nov 1 | Sep 20 |
| Hamilton | 6b | Apr 25 | Oct 28 | Sep 16 |
| London | 6a | Apr 22 | Oct 18 | Sep 6 |
| Kingston | 6a | May 10 | Oct 10 | Aug 29 |
| Ottawa | 5a | May 9 | Oct 12 | Aug 31 |
| Barrie | 5b | May 21 | Sep 24 | Aug 13 |
| Sudbury | 4b | May 31 | Sep 17 | Aug 6 |
| Thunder Bay | 3b | May 28 | Sep 20 | Aug 9 |
The fall dates use this site’s rule for every lawn page: seed at least six weeks before the average first fall frost, so the grass has time to root before winter. The frost dates are Environment and Climate Change Canada normals; every date in the table is counted from them, not typed.
Southern Ontario: September Works
Along Lake Ontario and Lake Erie the fall is long. Toronto, Hamilton and Windsor can seed into the middle of September, and the cooler nights of late summer suit cool-season grass. Seed into a lawn you have just aerated and the seed lands in the holes, where it stays moist. See aerating and overseeding by city.
Ottawa, Kingston and the North: August
East and north, the first frost comes in late September or early October, so the six-week deadline falls in August. In Sudbury, Barrie and Thunder Bay that means seeding in early August, often during the hottest, driest part of summer. If you cannot water a new lawn through August, spring seeding is the safer choice.
Spring Seeding
In spring, the University of Saskatchewan says grass seed germinates best once the soil is above 10°C. Soil lags behind the air, so it suggests waiting for daytime temperatures of about 15°C. That usually means two to four weeks after the last spring frost.
Spring-seeded grass meets summer heat before it has deep roots, so water it through its first July and August.
Getting the Seed to Take
Keep the seed moist until it comes up: the University of Saskatchewan says to water daily, or even twice a day, and that new grass takes about two weeks to germinate and be ready to walk on. Press the seed into the soil so it makes good contact; seed sitting on top of thatch rarely takes.
Choose a mix that suits the site; see the best grass seed for Ontario. For the rest of the year’s lawn jobs, see the lawn care calendar.
Shade
Shaded lawns are the exception to fall seeding. The University of Massachusetts recommends overseeding thin, shaded turf in early to mid spring, as soon as the soil reaches about 10°C, because more light reaches the ground through bare or young tree canopies than in late summer. See grass seed for shade.
Further east: when to plant grass seed in Quebec · in Atlantic Canada.
Frequently Asked Questions
When should I plant grass seed in Ontario?
Late summer to early fall. In southern Ontario, late August to mid-September; in Ottawa and Kingston by late August, and further north by early to mid-August. Seed at least six weeks before your average first fall frost.
Is September too late to plant grass seed in Ontario?
In Toronto, Hamilton and Windsor, the first half of September is fine. In Ottawa, Barrie, Sudbury and Thunder Bay the deadline falls in August.
When should I plant grass seed in Ottawa?
By the end of August. Ottawa's first fall frost comes in mid-October, so the six-week deadline falls in late August.
Can I plant grass seed in spring instead?
Yes. Seed once the soil is above 10°C, which the University of Saskatchewan says usually means daytime temperatures of about 15°C. Spring-seeded grass needs regular watering through its first summer.
What if I miss the fall deadline?
Wait for spring rather than seeding late into fall. Seed sown too close to freeze-up comes up tender and often does not survive the winter.
How long does grass seed take to grow?
About two weeks to germinate and be ready to walk on, according to the University of Saskatchewan, if the seed is kept moist.
Sources
- University of Saskatchewan, Gardening at USask — Lawns
- University of Massachusetts Amherst Extension — Growing Turf Under Shaded Conditions
- Environment and Climate Change Canada — Canadian Climate Normals (the frost dates in the tables, read from this site’s frost data)