GreenlyFrost dates and when to plant in Brittany
France
In Brittany the last spring frost comes between 21 February (Brest (France)) and 12 March (Rennes) — the median of 2016–2025 in 3 cities. The first autumn frost comes between 28 November (Rennes) and 13 December (Brest (France)). The frost-free season lasts 261–295 days. Tomato: plant out into open ground 13 May – 23 August, earliest in Rennes, latest in Brest (France).
Frost dates by city in Brittany
| City | Last spring frost | First autumn frost | Frost-free days | Climate zone | Tomato: window |
|---|---|---|---|---|---|
| Brest (France) | 21 February | 13 December | 295 | 270 frost-free days or more | 26 May – 23 August |
| Quimper | 8 March | 9 December | 276 | 270 frost-free days or more | 19 May – 19 August |
| Rennes | 12 March | 28 November | 261 | 210–269 frost-free days | 13 May – 8 August |
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 Brittany: 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 | 13 May (Rennes) – 23 August (Brest (France)) |
| Cucumber | 1 June (Rennes) – 28 September (Brest (France)) |
| Bell Pepper, Eggplant | 1 June (Rennes) – 23 August (Brest (France)) |
| Zucchini | 1 June (Rennes) – 26 September (Brest (France)) |
| Pumpkin | 1 June (Rennes) – 18 August (Brest (France)) |
| Watermelon | 1 June (Rennes) – 3 September (Brest (France)) |
| Peas | 31 January (Brest (France)) – 30 September (Brest (France)) |
| Garlic | Autumn planting: 29 October (Rennes) – end of December (Rennes) |
| Tulip, Daffodil, Crocus, Hyacinth | Autumn planting: by 29 October (Rennes) |
Weather by month in Brittany
Across the 3 cities the warmest month is July (average days 20.9 … 24.3 °C) and the coldest January (average nights 2.9 … 4.8 °C). No city here averages below 0 °C at night in any month.
| Month | Day, °C | Night, °C | Rain, mm |
|---|---|---|---|
| January | 8.8 … 9.6 °C | 2.9 … 4.8 °C | 126 |
| February | 10.4 … 10.5 °C | 3.6 … 5.4 °C | 98 |
| March | 11.6 … 12.7 °C | 4.6 … 5.9 °C | 97 |
| April | 14.2 … 15.7 °C | 6.1 … 6.7 °C | 68 |
| May | 16.8 … 19.1 °C | 9.4 … 9.6 °C | 69 |
| June | 19.3 … 22.8 °C | 12.2 … 12.9 °C | 83 |
| July | 20.9 … 24.3 °C | 13.9 … 14.3 °C | 65 |
| August | 20.8 … 24.4 °C | 14 … 14.4 °C | 65 |
| September | 18.9 … 21.5 °C | 12.4 … 12.6 °C | 79 |
| October | 15.9 … 17.4 °C | 9.8 … 10.5 °C | 116 |
| November | 12.4 … 12.6 °C | 6.1 … 8.1 °C | 130 |
| December | 9.9 … 10.7 °C | 4.5 … 6.5 °C | 143 |
Day and night: the lowest … highest monthly average among the cities; rain: the middle city (ERA5 via Open-Meteo).
