To reseed a lawn in Ontario, seed between mid-August and mid-September, when the Guelph Turfgrass Institute says new grass establishes best. Mow short, loosen the soil so seed can reach it, spread the seed in two passes, rake it in lightly, roll it, and keep the top of the soil moist until the seedlings are up. Spring seeding also works for bare patches, as long as the soil has thawed and is not waterlogged.
This guide covers when to reseed, which seed to choose, each step of the job, how to water new seed, and what to expect in the weeks after.
When to Reseed a Lawn in Ontario
The Guelph Turfgrass Institute at the University of Guelph puts the best window for establishing a lawn from seed in Ontario at mid-August to mid-September. The University of Minnesota Extension gives the same mid-August to mid-September window for its similar climate.
Spring is the second choice. The Guelph Turfgrass Institute says you can seed in spring if you see bare patches or winter damage, but the soil should be thawed and not saturated, because seed may not germinate in cold, wet soil. Spring seedlings also face summer heat sooner, so they need more attention.
Reseed, Overseed or Lay Sod?
- Reseeding means seeding bare or badly damaged areas, often after removing dead grass and loosening the soil.
- Overseeding means spreading seed into an existing lawn that has thinned out, without starting over.
- Laying sod gives an instant lawn and suits slopes and areas prone to erosion. The University of Minnesota Extension notes sod can be laid at almost any time in the growing season, but it costs more than seed.
If most of the lawn is bare, weedy or uneven, sod may be faster. Our guide to what sod is and how it is installed and our post on sod installation cost in Durham Region help you compare.
Choosing Grass Seed
Pick seed for the conditions in each part of your yard:
- Sunny lawns with family traffic: the Guelph Turfgrass Institute often recommends a mixture of Kentucky bluegrass and perennial ryegrass. The University of Minnesota Extension adds turf-type tall fescue as a good choice for sunny, high-wear areas.
- Shady areas: look for seed mixtures labelled for shade tolerance, as the University of Minnesota Extension advises.
- Low-maintenance areas: fine fescues or turf-type tall fescues give a durable lawn with less care.
Buy fresh seed from a nursery or garden centre and check the label for the species mix. Our guide to choosing the right type of grass explains the main species.
How to Reseed a Lawn, Step by Step
- Test the soil. The University of Minnesota Extension recommends a soil test first, then amending the soil as the results suggest.
- Mow low and clear debris. Cut the existing grass shorter than usual and rake out dead grass, leaves and thatch so seed can reach the soil.
- Loosen the surface. Rake bare spots firmly or core aerate thinning areas. Seed needs contact with soil, not a mat of old grass.
- Firm the soil. Roll or lightly firm the area so it is level and not fluffy.
- Spread the seed in two passes. The University of Minnesota Extension suggests spreading half the seed in one direction and half at right angles to it, for even coverage. Use the rate on the seed bag.
- Rake it in lightly. Lightly rake so about 10 to 15% of the seed still shows on the surface, then roll again for good seed-to-soil contact.
- Water. Soak the soil once, then switch to light, frequent watering (details below).
Watering New Grass Seed
Water decides whether reseeding works. The University of Minnesota Extension recommends watering to a depth of 4 to 6 inches right after seeding, then keeping the surface moist with light watering up to 3 or 4 times a day, cutting back when it rains. After germination, it advises watering less often as the roots grow into the soil.
Do not let the seedbed dry out while the seed is germinating. The light, frequent watering above is what keeps it moist.
How Long Until the New Grass Grows?
Germination time depends on the species. Seed producer Barenbrug lists these typical ranges:
| Grass | Typical germination time |
|---|---|
| Perennial ryegrass | 5 to 10 days |
| Tall fescue | 7 to 21 days |
| Fine fescue | 7 to 21 days |
| Kentucky bluegrass | 14 to 30 days |
A mixture fills in gradually: ryegrass shows first, and bluegrass catches up over the following weeks. The University of Minnesota Extension notes that it takes nearly a full season for a seeded lawn to become mature and durable, so expect to keep foot traffic light for a while.
Mowing and Feeding New Grass
Make the first cut high, and never cut more than a third of the blade length at one time, the rule the Guelph Turfgrass Institute gives. Use a sharp blade so seedlings are cut cleanly rather than torn out. For feeding, the University of Wisconsin-Madison Extension names early September as the most important time to fertilize cool-season lawns, which fits neatly with late-summer reseeding.
Mistakes to Avoid
- Seeding outside the window. Aim for the mid-August to mid-September window the Guelph Turfgrass Institute recommends, with spring as the fallback.
- Burying the seed. Seed raked in too deep may not come up. A light raking that leaves some seed visible is enough.
- Letting the surface dry out during germination.
- Using banned weed killers. Ontario bans the cosmetic use of pesticides containing ingredients such as 2,4-D and glyphosate on lawns. Use only products whose active ingredients are on the province's allowable list.
- Mowing too soon or walking on the new grass before it has rooted.
Common Questions
Can I just throw grass seed on my lawn?
Seed scattered on top of thatch or hard soil often dries out or washes away. Rake or aerate first so the seed touches soil, then rake it in lightly and keep it moist.
Is it better to reseed in spring or fall in Ontario?
Late summer to early fall. The Guelph Turfgrass Institute says mid-August to mid-September is generally the best time to establish a lawn from seed in Ontario, with spring as a fallback for bare patches.
How long does it take to reseed a lawn?
The work itself takes a day for most yards. Seedlings appear in 5 to 30 days depending on the species, and the lawn needs most of a season to become fully durable.
Should I aerate before reseeding?
Core aeration helps when you are overseeding a thin, compacted lawn, because the holes give seed a place to meet the soil. On bare patches, loosening the surface with a rake does the same job.
Let Us Reseed Your Lawn
Fall aeration and overseeding are part of the seasonal programs in our lawn maintenance service, and our sod installation service is there when a lawn needs to start over. Our fall lawn care guide covers the rest of the season. Contact us for a free quote anywhere in Durham Region.
Sources: Guelph Turfgrass Institute, Spring care tips for your yard; University of Minnesota Extension, Seeding and sodding home lawns; Barenbrug, Frequently asked questions; University of Wisconsin-Madison Extension, Lawn Maintenance; Ontario.ca, Pesticides (home lawns and gardens).
