Spring lawn care in Ontario begins in late March in Windsor and the southwest, and stretches into early May for Ottawa and the eastern counties. The snow retreats unevenly across the province, leaving matted grass, residual de-icing salt along driveways, and the occasional patch of grey or pink snow mould — especially where plows piled snow or where leaves were left under a thick blanket. The soil warms slowly here; it usually crosses the 10°C threshold that wakes Kentucky Bluegrass around late April in the Greater Toronto Area and a week or two later in Ottawa.
Because Ontario is dominated by cool-season grasses — Kentucky Bluegrass first, with Tall Fescue and Perennial Ryegrass filling in — spring is the single best window to recognise winter damage, repair thin patches, and set up the lawn for a resilient summer. The timing of pre-emergent crabgrass control, tied to forsythia bloom, is the most pivotal decision of the season. Get that date right and you will fight far fewer weeds in July.
Spring Timeline for Ontario
- March: Inspect the lawn as snow melts, note snow mould patches, keep traffic off soggy turf, and service mowers and trimmers.
- April: Rake lightly, flush salt-damaged edges, apply pre-emergent at forsythia bloom, and take the first mow at 65mm once growth begins.
- May: First fertiliser application once soil holds 10°C, overseed bare patches, and begin routine mowing at 75mm.
Pre-emergent timing at forsythia bloom
The defining spring task in Ontario is applying a crabgrass pre-emergent at exactly the right moment — and that moment is visually signalled by the forsythia shrub finishing its yellow bloom. When forsythia petals begin to drop, soil temperature at 5cm depth has reached about 12°C, which is the germination threshold for crabgrass. In the southwest (Windsor, London, Sarnia) this usually happens in early-to-mid April. In the Greater Toronto Area it typically falls in mid-April. In Ottawa and eastern Ontario, watch for forsythia in late April.
Apply pre-emergent before the petals have fully dropped — you want the barrier in the soil before the first crabgrass seeds germinate. Water the product in with 6mm of irrigation unless rain is forecast within 24 hours. A split application, with the second half six weeks later, extends protection through the full germination window and is the approach professional services use in southern Ontario where summers run long and hot.
If you plan to overseed bare patches this spring, skip pre-emergent in those specific areas — the same chemistry that blocks crabgrass will block your Kentucky Bluegrass or Tall Fescue seed. Either use a mesotrione-based product that tolerates new seed or save the overseed for late summer, which is a better window anyway in Ontario.
Spring Grass Care in Ontario
Kentucky Bluegrass is the dominant lawn grass across Ontario, prized for its deep blue-green colour, self-repairing rhizomes, and hardiness through cold winters. It is slow to wake in spring, though: do not panic if your neighbour's Perennial Ryegrass is already green while your Kentucky Bluegrass still looks tan — the bluegrass is building its root system first and will catch up by mid-May. Avoid heavy traffic on partially dormant turf; the crowns are vulnerable to bruising.
Tall Fescue has gained ground in Ontario over the last decade because it tolerates heat and drought better than bluegrass, making it a strong choice for unirrigated lawns. In spring, Tall Fescue greens up earlier than bluegrass and benefits from a light fertiliser at the same 10°C soil trigger. Fine Fescue in shady areas along fence lines and under maples should be raked very gently — its slender blades tear easily.
Ontario-Specific Spring Challenges
Snow mould is the most visible spring problem in Ontario, particularly after winters with long, steady snow cover. Grey snow mould (Typhula) looks like matted straw-coloured patches with white webbing; pink snow mould (Fusarium) carries a salmon tint and is more aggressive. For both, rake firmly once the lawn is dry enough to walk on — this breaks the mats and restores air flow, and most lawns recover without fungicide.
European Chafer grubs, which hatched the previous summer, may still be feeding in the upper soil profile in April. Damage shows as irregular tan patches that lift like loose carpet, often accompanied by skunk or raccoon digging. Spring is not the right window to apply nematodes — save that for August — but note the damaged areas so you can reseed and plan a targeted treatment later in the season.
Key Dates for Ontario Spring
| Task | Typical Timing | Condition Trigger |
|---|---|---|
| Service mowers and equipment | Mid-March | Before snow fully melts |
| Light spring rake | Early April | Lawn firm enough to walk on without leaving prints |
| Flush road salt from lawn edges | Early April | Before growth resumes |
| Pre-emergent crabgrass control | Mid-April (SW) to late April (Ottawa) | Forsythia bloom ending |
| First mow at 65mm | Mid-to-late April | Grass reaches 90mm height |
| First fertiliser application | Late April to mid-May | Soil temperature holds 10°C at 5cm |
| Overseed bare patches | Early May | Soil consistently above 10°C |
| Raise mowing height to 75mm | Late May | Daytime highs consistently above 20°C |
FAQs — Ontario Spring
When should I apply pre-emergent in Ontario?
Apply pre-emergent crabgrass control when forsythia finishes blooming — typically early-to-mid April in southwestern Ontario and mid-to-late April in Ottawa and the east. At this point, soil at 5cm depth has reached around 12°C, the germination threshold for crabgrass. Water the product in with 6mm of irrigation if no rain is forecast in 24 hours.
My lawn has grey matted patches after snow melt — what are they?
Those are snow mould patches, most commonly grey snow mould (Typhula) in Ontario. Rake the affected areas firmly once the lawn is dry enough to walk on to break up the mats and restore air flow. Most patches recover without fungicide. Prevent recurrence next year by cutting to 60mm for the final mow, removing all leaves, and avoiding large snow piles on the lawn.
When is the first fertiliser application in Ontario?
Apply the first spring fertiliser once soil temperature at 5cm holds 10°C. In southwestern Ontario this is usually late April; in Ottawa and eastern Ontario it is early-to-mid May. Fertilising earlier wastes product because the grass cannot yet absorb it, and it may encourage disease on cold, wet turf.
Can I overseed in spring in Ontario?
You can, but late August through mid-September is a better window in Ontario because soil is still warm, weed pressure is lower, and young seedlings are not fighting summer heat. If you must overseed now, wait until soil reaches 10°C, avoid pre-emergent in those areas, and keep the seedbed moist for 2–3 weeks.
Should I worry about grubs in spring?
European Chafer grubs from last year's hatch may still be feeding in April, showing as loose patches that lift like carpet. Spring is not the right window for beneficial nematodes — wait until August when new grubs are small and soil is warm and moist. For now, note the damaged areas and reseed them in May.