GreenlyFrost dates and when to plant in Northern Ireland
United Kingdom
In Northern Ireland the last spring frost comes between 23 March (Derry) and 18 April (Belfast) — the median of 2016–2025 in 2 cities. The first autumn frost comes between 19 November (Belfast) and 21 November (Derry). The frost-free season lasts 215–243 days. Tomato: plant out into open ground 7 June – 1 August, earliest in Derry, latest in Derry.
Frost dates by city in Northern Ireland
| City | Last spring frost | First autumn frost | Frost-free days | Climate zone | Tomato: window |
|---|---|---|---|---|---|
| Derry | 23 March | 21 November | 243 | 210–269 frost-free days | 7 June – 1 August |
| Belfast | 18 April | 19 November | 215 | 210–269 frost-free days | 15 June – 30 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 Northern Ireland: 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 | 7 June (Derry) – 1 August (Derry) |
| Cucumber | 7 July (Belfast) – 6 September (Derry) |
| Bell Pepper, Eggplant | 7 July (Belfast) – 1 August (Derry) |
| Zucchini | 7 July (Belfast) – 4 September (Derry) |
| Pumpkin | 7 July (Belfast) – 27 July (Derry) |
| Watermelon | 7 July (Belfast) – 12 August (Derry) |
| Peas | 2 March (Derry) – 8 September (Derry) |
| Garlic, Tulip, Daffodil, Crocus, Hyacinth | Autumn planting: 20 October (Belfast) – end of December (Belfast) |
Weather by month in Northern Ireland
Across the 2 cities the warmest month is July (average days 17.7 … 18.3 °C) and the coldest January (average nights 2.3 … 3.2 °C). No city here averages below 0 °C at night in any month.
| Month | Day, °C | Night, °C | Rain, mm |
|---|---|---|---|
| January | 6.9 … 7.4 °C | 2.3 … 3.2 °C | 79 |
| February | 7.8 … 8.1 °C | 2.7 … 3.4 °C | 89 |
| March | 9.3 … 9.5 °C | 3 … 3.6 °C | 86 |
| April | 11.1 … 11.5 °C | 4.2 … 4.9 °C | 71 |
| May | 14.9 °C | 7.2 … 7.7 °C | 76 |
| June | 16.8 … 17.2 °C | 10.1 … 10.4 °C | 92 |
| July | 17.7 … 18.3 °C | 11.5 … 11.7 °C | 103 |
| August | 17.7 … 18 °C | 11.5 … 11.9 °C | 109 |
| September | 15.8 … 15.9 °C | 9.8 … 10.3 °C | 100 |
| October | 12.8 … 12.9 °C | 7.8 … 8.4 °C | 102 |
| November | 9.3 … 9.7 °C | 4.6 … 5.4 °C | 90 |
| December | 7.8 … 8.2 °C | 3.5 … 4.2 °C | 98 |
Day and night: the lowest … highest monthly average among the cities; rain: the middle city (ERA5 via Open-Meteo).
What to plant month by month: the UK
Other regions: United Kingdom
More about the United Kingdom
- Gardening in the United Kingdom: climate zones and crops by region
- United Kingdom: frost dates by city
- When to plant tomatoes in the United Kingdom
- When to plant cucumbers in the United Kingdom
- When to plant bell peppers in the United Kingdom
- When to plant peas in the United Kingdom
- When to plant garlic in the United Kingdom
- Gardening by country
