GreenlyDenver: frost dates
United States
| Last spring frost | around 1 May |
|---|---|
| First autumn frost | around 15 October |
| Frost-free days | 167 days |
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 sow and plant
| Crop | Sow for seedlings | Plant out in a greenhouse | Open ground |
|---|---|---|---|
| Bell Pepper | 22 February | 7 May | 28 May |
| Chili Pepper | 5 March | 18 May | 8 June |
| Corn | — | 17 April | sow 8 May |
| Cucumber | 26 March | 7 May | 28 May |
| Eggplant | 26 February | 7 May | 28 May |
| Green Beans | 11 March | 17 April | 8 May |
| Melon | 16 March | 7 May | 28 May |
| Peas | — | 20 March | sow 10 April |
| Physalis | 3 March | 17 April | 8 May |
| Pumpkin | 11 March | 17 April | 8 May |
| Sweet Corn | — | 17 April | sow 8 May |
| Tomato | 19 February | 17 April | 8 May |
| Watermelon | 5 April | 7 May | 28 May |
| Zucchini | 16 March | 17 April | 8 May |
Planting out: a week after the last frost once the soil is warm enough for the crop; frost-hardy crops three weeks before it; an unheated greenhouse three weeks earlier. Seedlings are sown so they are ready on that day.
Planted in autumn
| Crop | Plant around |
|---|---|
| Crocus | 15 September |
| Daffodil | 15 September |
| Garlic | 15 September |
| Hyacinth | 15 September |
| Lily | 15 September |
| Tulip | 15 September |
A month before the first autumn frost, so the roots grow before winter.