Last Frost Date Windsor — April 20 (Zone 7a)

May 1–5 in the central core, a few days longer in rural interior Essex County. Windsor's mild Zone 7a climate makes it one of the earliest safe-transplant cities in Canada outside coastal BC. Tomatoes need both frost-free conditions and warm soil (above 12°C at 5 cm depth). Windsor's exceptional ~190-day season allows any variety, including 85–90 day heirlooms. Always harden off seedlings for 7–10 days before transplanting.

Windsor sits at the southwestern tip of Ontario — further south than parts of northern California — wrapped almost entirely by water: the Detroit River, Lake St. Clair, and Lake Erie. That surrounding water moderates the climate, and the southerly latitude brings long, hot summers. The combination earns Windsor a Zone 7a hardiness rating, the warmest of any major inland Canadian city, with milder winters, hotter summers, and a longer frost-free season than anywhere else in Ontario.

Yes — Windsor is one of the only Canadian cities where sweet potatoes, okra, and peanuts are routine rather than experimental. The ~190-day season and Zone 7a heat give these warm-season crops the long stretch of genuine warmth they need. Transplant sweet potato slips and okra after May 10 into warm soil, choose fast-maturing varieties, and harvest before the late-October first frost. These crops are risky or impossible in Toronto, Hamilton, and everywhere north or east of Windsor.

Around October 28 for the central core — one of the latest first-fall-frost dates of any Canadian city, and a key part of Windsor's exceptional ~190-day growing season. Lake Erie and the Detroit River hold their summer warmth well into autumn, delaying the first frost. Rural interior Essex County frosts a little earlier. Covering tomatoes and peppers with row cover during the first light frosts of late October can stretch the harvest even further.

Environment and Climate Change Canada (ECCC) climate normals for the 1991–2020 reference period, supplemented by station-level observations from Windsor Airport (YQG), the Harrow CDA research station, and surrounding Essex County stations. The April 20 average reflects central-core conditions. Lake Erie shore and Pelee Island dates incorporate Leamington-area and island observations; rural interior dates are adjusted for distance from the lakes and cold-air drainage.

Windsor's last spring frost date is April 20 for the central core — Zone 7a, the warmest hardiness zone of any major inland Canadian city. This is the historical 50th-percentile average from Environment and Climate Change Canada climate normals (1991–2020). The Detroit River waterfront and downtown run 1–3 days earlier (April 17–21) thanks to the river, Lake Erie, and the urban heat island. Suburban and rural Essex County run a few days later. The Lake Erie shore towns of Leamington and Kingsville are as mild as the Windsor core, and Pelee Island — Canada's southernmost inhabited point — is milder still. The full historical range for the central core spans early April to early May.

The historical average last frost in Windsor is April 20, and that average is what 2026 planning should be based on — frost dates are climate normals that do not change year to year. Individual years vary by 1–2 weeks earlier or later. For 2026 specifically, monitor Environment Canada forecasts through the first week of May. After May 1, frost risk in Windsor's central core is very low in any year — Windsor is one of Canada's most frost-reliable cities in spring. Rural Essex County gardeners should add a few days of buffer.

If today's date is past April 20, the average last frost has passed in Windsor's central core. In any given year there is only roughly a 10% chance of a frost after April 20 — Windsor's Zone 7a climate, Detroit River, and Lake Erie moderation make late spring frosts uncommon. For frost-sensitive plants like tomatoes, peppers, and basil, wait until May 1–5 in the city and a few days longer in rural Essex County. After May 5, frost risk is very low across the whole region.

Windsor-area frost dates vary by distance from the water. Downtown / Detroit River waterfront / Walkerville: April 17–21 (Zone 7a — strongest river and urban moderation). Riverside and the east riverfront: April 18–22 (Zone 7a). South Windsor and Devonshire: April 19–23 (Zone 7a). LaSalle: April 19–23 (Zone 7a). Tecumseh and Lakeshore: April 19–24 (Zone 7a). Amherstburg: April 18–22 (Zone 7a). Leamington and Kingsville on the Lake Erie shore: April 17–22 (Zone 7a — Canada's greenhouse and tomato capital). Pelee Island: April 12–18 (Zone 7b — Canada's southernmost inhabited point and mildest pocket). Rural interior Essex County: April 22–28 (Zone 6b/7a — open farmland, cold-air drainage).

April 20 is the 50th-percentile historical average — meaning roughly half of all years see the last spring frost before April 20, and half after. The full historical range for Windsor's central core spans from around April 3 (earliest recorded) to around May 6 (latest). That's a contained 33-day window — narrower than continental Canadian cities, because the Detroit River and Lake Erie strongly moderate Windsor's spring. Treat April 20 as a planning anchor, not a guarantee. Windsor's mild Zone 7a climate makes it one of the safer Canadian cities for an early transplant, but a late-April cold snap is still possible.

Windsor is officially Zone 7a — the warmest hardiness zone of any major inland Canadian city, on par with parts of coastal British Columbia. This means average annual minimum temperatures of -17.8°C to -12.2°C, milder than Toronto (6b), Hamilton (6b/7a), or any Prairie city. The Detroit River core sits firmly in Zone 7a, the Lake Erie shore at Leamington and Kingsville matches it, and Pelee Island reaches Zone 7b. Rural interior Essex County drops slightly to Zone 6b/7a. Windsor's Zone 7a designation allows plants to overwinter — and crops to be grown — that are risky or impossible elsewhere in Ontario.

Frost-tolerant cool-season crops can go in 4–6 weeks before the April 20 last frost — meaning early-to-mid March in Windsor. Direct sow as soon as soil is workable (typically early-to-mid March): peas, spinach, radishes, lettuce, arugula, kale. Direct sow mid-to-late March: carrots, beets, Swiss chard, turnips. Transplant late March/early April: broccoli, cauliflower, cabbage, kohlrabi, onions. Wait until after May 1–5 for tomatoes, peppers, basil, beans, and squash. Windsor's exceptional ~190-day Zone 7a season makes it one of the only Canadian cities where sweet potatoes, okra, peanuts, and melons are routine crops rather than experiments. Hardneck garlic planted mid-October overwinters easily.

Late frost after April 20 happens in only roughly 1 in 10 years in Windsor's central core — among the lowest rates of any Canadian city. When it does happen, the frost is mild, rarely below -2°C. Protection options: floating row cover (Reemay, Agribon) over transplants protects to about -3°C and is more than enough. Cloches or inverted pots over individual seedlings for predicted overnight frosts. Plant tender crops in the warmest spot — a south-facing wall or a river-adjacent garden. Watch the forecast for clear, still nights after warm April days. Rural Essex County gardeners should be slightly more cautious than those in the river-moderated city core. Row cover and cloches are available at garden centres across Windsor and Essex County.

Windsor's April 20 last frost is among the earliest of any Canadian city — tied with Toronto and Mississauga, and behind only coastal BC. But Windsor's real distinction is its Zone 7a rating and its ~190-day growing season, among the longest in Canada. Compared to other Canadian cities: 36 days later than Vancouver (March 15), tied with Toronto (April 20), 5 days earlier than Hamilton (April 25), 19 days earlier than Montreal and Ottawa (May 9), 33 days earlier than Calgary (May 23). Windsor is Canada's warmest inland city — the combination of an early last frost, a late October 28 first fall frost, and Zone 7a heat lets Windsor gardeners grow sweet potatoes, okra, and peanuts that fail everywhere else in Ontario.