GreenlyFrost dates and when to plant in Alberta
Canada
In Alberta the last spring frost comes between 7 May (Edmonton) and 13 May (Calgary) — the median of 2016–2025 in 2 cities. The first autumn frost comes between 1 October (Calgary) and 6 October (Edmonton). The frost-free season lasts 141–152 days. Tomato: plant out into open ground 3 June – 16 June, earliest in Calgary, latest in Edmonton.
Frost dates by city in Alberta
| City | Last spring frost | First autumn frost | Frost-free days | Climate zone | Tomato: window |
|---|---|---|---|---|---|
| Edmonton | 7 May | 6 October | 152 | 150–209 frost-free days | 3 June – 16 June |
| Calgary | 13 May | 1 October | 141 | Short season: under 150 frost-free days | 3 June – 11 June |
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 Alberta: 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 | 3 June (Calgary) – 16 June (Edmonton) |
| Cucumber | 18 June (Calgary) – 22 July (Edmonton) |
| Bell Pepper, Eggplant | 18 June (Calgary) – 28 July (Edmonton) |
| Zucchini | 18 June (Calgary) – 20 July (Edmonton) |
| Pumpkin | 18 June (Calgary) – 23 July (Edmonton) |
| Watermelon | 18 June (Calgary) – 27 June (Edmonton) |
| Peas | 16 April (Edmonton) – 24 July (Edmonton) |
| Garlic, Tulip, Daffodil, Crocus, Hyacinth | Autumn planting: 1 September (Calgary) – 26 October (Calgary) |
Weather by month in Alberta
Across the 2 cities the warmest month is July (average days 23.6 … 24.5 °C) and the coldest February (average nights -15.5 … -13.4 °C). Every city averages below 0 °C at night in November–April.
| Month | Day, °C | Night, °C | Rain, mm |
|---|---|---|---|
| January | -5.6 … -1.3 °C | -14.2 … -11.7 °C | 18 |
| February | -6.1 … -1.9 °C | -15.5 … -13.4 °C | 20 |
| March | 1 … 5.2 °C | -9.3 … -7.7 °C | 24 |
| April | 9.9 … 11.4 °C | -2 … -1.9 °C | 31 |
| May | 18.4 °C | 4.2 … 5.9 °C | 60 |
| June | 21.4 … 21.8 °C | 8.7 … 10.5 °C | 107 |
| July | 23.6 … 24.5 °C | 11.4 … 13 °C | 86 |
| August | 23.1 … 24.6 °C | 10.9 … 11.9 °C | 64 |
| September | 18.5 … 19.8 °C | 6.8 … 7.4 °C | 36 |
| October | 9.7 … 11.3 °C | -0.1 … 0.3 °C | 29 |
| November | 0.2 … 3.5 °C | -7.5 … -6.3 °C | 26 |
| December | -6.2 … -2.3 °C | -14.4 … -11.8 °C | 24 |
Day and night: the lowest … highest monthly average among the cities; rain: the middle city (ERA5 via Open-Meteo).
