Dormant Seeding in Ontario: How to Seed Your Lawn in Late Fall
Dormant seeding means spreading grass seed in late fall, once it is too cold for the seed to sprout but before the ground freezes, so it sits in the soil over winter and germinates in spring. In southwestern Ontario that window usually falls in November, once daytime highs stay below about 10°C. It works best for thickening thin lawns and patching bare spots, not for starting a lawn from scratch.
If you missed the late-summer seeding window, or your lawn took a beating this year from drought, grubs or heavy use, dormant seeding gives you a second chance. Here is how it works, when to do it in London and area, which grass types suit it, and where it can go wrong.
How dormant seeding works
Grass seed needs warmth and steady moisture to germinate. If you seed in October and a warm week arrives, seed can sprout and the tender seedlings may then die in the first hard freeze. Dormant seeding avoids that by waiting until conditions are too cold to sprout. The seed then:
Sits dormant in the soil through winter.
Gets worked into the soil by freeze-thaw cycles, which improve seed-to-soil contact.
Germinates in early spring as soon as the soil warms, often earlier than spring-sown seed.
University of Minnesota Extension notes that dormant seeding takes advantage of the natural freeze-thaw cycle over winter to improve seed-to-soil contact.
When to dormant seed in southwestern Ontario
The goal is to seed after it's too cold for germination and before the soil freezes solid or snow covers the lawn.
Air temperature: University of Massachusetts turf guidance says to aim for air temperatures consistently below about 10°C (50°F).
Soil temperature: soil in the low single digits Celsius, around 4°C or less. University of Minnesota says dormant seeding can be done any time soil is below 40°F (about 4°C).
Timing: For Ontario, many turf suppliers recommend November, before the permanent freeze.
UMass also advises that it's better to err on the side of too late than too early. In London, average first fall frost arrives in early October, but that alone isn't the signal. Wait until the cold is steady.
Dormant seeding vs. early fall seeding
Typical timing: Early fall seeding: Mid-August to mid-September; Dormant seeding: November, before freeze-up
Germination: Early fall seeding: 2–3 weeks with steady moisture; Dormant seeding: Early spring
Main risk: Early fall seeding: Dry spells; needs watering; Dormant seeding: Winter warm spells, washout, dry spring
Best for: Early fall seeding: New lawns and overseeding; Dormant seeding: Thickening thin turf, patching bare spots
Watering: Early fall seeding: Daily light watering until established; Dormant seeding: None until spring
Iowa State University Extension calls mid-August to mid-September the best time to seed cool-season lawns. Dormant seeding is a backup plan, not a replacement for that window.
Which grass types suit dormant seeding?
Dormant seeding works with cool-season grasses common in Ontario lawns, but some handle it better than others.
Kentucky bluegrass: UMass says bluegrass is among the slowest grasses to establish and tends to suit dormant seeding. It's also the main grass in most Ontario sod.
Tall fescue: deep-rooted and drought-tolerant; Minnesota Extension lists it as suitable.
Fine fescues: good for shade, and also listed by Minnesota Extension.
Perennial ryegrass: UMass says it is among the least tolerant of low temperatures and generally does less well with dormant seeding, even though it sprouts quickly in fall.
A good-quality blend matched to your sun and shade is usually the best choice.
Step-by-step: how to dormant seed
Do your final mow. Keep mowing until the grass stops growing. Iowa State suggests lowering from about 7.5–9 cm (3–3.5 in) to 6–7.5 cm (2.5–3 in) in fall.
Clear the leaves. Bag or mulch leaves first. Seed sitting on matted leaves never reaches the soil. Our guide to fall leaf cleanup in London covers yard waste options.
Rough up bare spots. Rake firmly to expose soil. On larger areas, slice seeding gives better results than broadcasting, according to UMass.
Add a thin layer of topsoil or compost to low or bare patches. Keep it thin, about 0.5–1 cm.
Spread seed at a higher rate. UMass recommends higher seeding rates to make up for losses over winter.
Rake or roll the seed in lightly for good contact.
Leave it alone until spring. No watering is needed.
What can go wrong
A warm winter spell. UMass says the main risk is a warm stretch that starts germination too early, after which seedlings can die.
Little snow cover. A winter with little snow can dry seed out.
Washout on slopes. Heavy rain or melt can carry seed downhill. A light straw or compost topdressing helps and also deters birds.
A dry spring. Minnesota Extension notes seedlings can dry out during a warm, dry spring, so water once they sprout.
Spring weed control. Most crabgrass preventers also stop grass seed from germinating, so skip them on seeded areas next spring.
Spring follow-up after dormant seeding
Dormant seeding doesn't end in November. What you do in April and May decides how well it works:
Watch for seedlings once the snow is gone and the soil warms. Areas in full sun usually sprout first.
Keep the surface moist once seedlings appear. Light, frequent watering is better than an occasional soak until the new grass is established.
Stay off seeded areas as much as possible. Young grass and soft spring soil are easily damaged by foot traffic.
Hold off on mowing until the new grass is tall enough to cut without pulling it out, then mow with a sharp blade.
Skip crabgrass preventer on seeded patches. Hand-pull weeds instead, or wait until the new grass has been mowed a few times before using weed control products, following label directions.
Reseed thin spots in late August or early September if some areas didn't fill in.
If a spring check shows large bare areas, sod is often the quickest fix. It gives you a finished lawn in a day, and the roots knit into the soil within a few weeks with regular watering.
Should you seed, sod, or wait?
Dormant seeding is cheap and simple, but you won't see results until May. If you need a lawn quickly, sod is the faster route. There is still time to lay sod in mid-October while the ground is workable. Our sod vs. seed comparison breaks down the trade-offs, and our sod installation page explains how we prepare and install.
Use this rule of thumb:
Thin lawn, patchy areas: dormant seed in November.
Large bare areas, slopes, or new construction: sod now, or plan sod for spring.
Grub-damaged turf: repair the soil and reseed or sod. See our post on fall grub damage.
Local angle: London's soils
On London's heavy clay, seed can sit on a hard, crusted surface and never make contact. Loosening the surface and adding a thin layer of screened topsoil makes a big difference. On the sandier soils west of the city, toward Strathroy and Komoka, seed has better contact but dries out faster in spring, so plan on watering once seedlings appear.
FAQ
When should I dormant seed my lawn in London, Ontario?
Usually in November, once daytime highs stay below about 10°C and soil is cold, but before the ground freezes or snow covers it. It's better to seed slightly late than too early.
Do I need to water dormant seed?
No. Seed stays dormant through winter. Start watering in spring once seedlings emerge, especially if the weather turns warm and dry.
Can I dormant seed a brand-new lawn?
You can, but UMass Extension recommends dormant seeding mainly for thickening existing turf and filling bare spots. For a new lawn, early fall seeding or sod is more reliable.
Will birds eat dormant seed?
Some seed may be lost to birds. Raking seed in and adding a thin layer of compost or straw helps protect it.
Can I use crabgrass preventer in spring after dormant seeding?
Most crabgrass pre-emergent herbicides also stop grass seed from germinating, so avoid them on seeded areas.
Need a lawn fast? Talk to SPM
SPM Landscape & Excavation has installed sod and prepared lawns across London and southwestern Ontario since 2006. We are WSIB covered and carry $1 million in liability insurance. We supply screened topsoil and can grade, prepare and sod your yard. Call (519) 474-0008 or email spmlandscape@gmail.com.
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