GreenlyFrost dates and when to plant in Ontario
Canada
In Ontario the last spring frost comes between 19 April (Hamilton) and 11 May (Thunder Bay) — the median of 2016–2025 in 7 cities. The first autumn frost comes between 23 October (Thunder Bay) and 7 November (Windsor). The frost-free season lasts 165–202 days. Tomato: plant out into open ground 14 May – 18 July, earliest in Windsor, latest in Hamilton.
Frost dates by city in Ontario
| City | Last spring frost | First autumn frost | Frost-free days | Climate zone | Tomato: window |
|---|---|---|---|---|---|
| Hamilton | 19 April | 7 November | 202 | 150–209 frost-free days | 19 May – 18 July |
| Windsor | 24 April | 7 November | 197 | 150–209 frost-free days | 14 May – 18 July |
| Toronto | 26 April | 30 October | 187 | 150–209 frost-free days | 20 May – 10 July |
| London (Canada) | 28 April | 7 November | 193 | 150–209 frost-free days | 19 May – 18 July |
| Kitchener | 30 April | 26 October | 179 | 150–209 frost-free days | 22 May – 6 July |
| Ottawa | 30 April | 1 November | 185 | 150–209 frost-free days | 27 May – 12 July |
| Thunder Bay | 11 May | 23 October | 165 | 150–209 frost-free days | 22 June – 3 July |
Median of 2016–2025 for the 25 km grid cell of the city: the last day at or below 0 °C in spring and the first in autumn (ERA5 reanalysis via Open-Meteo). In a cold year a frost can come a week or two later — Greenly warns 48 hours ahead.
When to plant in Ontario: windows by crop
The earliest start and the latest end among the cities here, each with its city; every city’s own window is on its page. Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.
| Crop | Planting out or sowing |
|---|---|
| Tomato | 14 May (Windsor) – 18 July (Hamilton) |
| Cucumber | 27 May (Windsor) – 23 August (Hamilton) |
| Bell Pepper, Eggplant | 27 May (Windsor) – 14 August (Thunder Bay) |
| Zucchini | 27 May (Windsor) – 21 August (Hamilton) |
| Pumpkin | 27 May (Windsor) – 9 August (Thunder Bay) |
| Watermelon | 27 May (Windsor) – 29 July (Hamilton) |
| Peas | 29 March (Hamilton) – 25 August (Hamilton) |
| Garlic, Tulip, Daffodil, Crocus, Hyacinth | Autumn planting: 23 September (Thunder Bay) – 10 December (Hamilton) |
Weather by month in Ontario
Across the 7 cities the warmest month is July (average days 23.6 … 28.6 °C) and the coldest February (average nights -15.4 … -5.2 °C). Every city averages below 0 °C at night in December–March.
| Month | Day, °C | Night, °C | Rain, mm |
|---|---|---|---|
| January | -6.9 … 1 °C | -15.1 … -5.3 °C | 71 |
| February | -6.2 … 3.2 °C | -15.4 … -5.2 °C | 68 |
| March | 0.6 … 8.6 °C | -8.4 … -0.6 °C | 78 |
| April | 6 … 14 °C | -2.7 … 3.9 °C | 95 |
| May | 14.3 … 20.7 °C | 4.3 … 10.6 °C | 81 |
| June | 19.9 … 26.6 °C | 10.4 … 16.5 °C | 90 |
| July | 23.6 … 28.6 °C | 14.4 … 19.3 °C | 86 |
| August | 22.3 … 27.2 °C | 14.2 … 18.5 °C | 85 |
| September | 18.2 … 24 °C | 10.9 … 15.5 °C | 67 |
| October | 10.5 … 17.2 °C | 4.2 … 9.4 °C | 85 |
| November | 2.5 … 9.1 °C | -3.6 … 2.4 °C | 61 |
| December | -4.1 … 3.7 °C | -11.6 … -2.2 °C | 75 |
Day and night: the lowest … highest monthly average among the cities; rain: the middle city (ERA5 via Open-Meteo).
