GreenlyDenver: frost dates
United States
In Denver the last spring frost usually comes around 1 May and the first autumn frost around 15 October, which leaves about 167 frost-free days (median of 2016–2025). Tomato seedlings can go into open ground around 8 May.
| 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 |
|---|---|---|---|
| Achocha | 8 March | 17 April | 8 May |
| Arugula | — | 20 March | sow 10 April |
| Basil | 30 March | 7 May | 28 May |
| Beet | — | 20 March | sow 10 April |
| Bell Pepper | 22 February | 7 May | 28 May |
| Black-eyed Susan | 7 March | — | 8 May |
| Bok Choy | 13 March | 17 April | 8 May |
| Broad bean | — | 20 March | sow 10 April |
| Broccoli | — | 20 March | sow 10 April |
| Brussels Sprouts | 3 February | 20 March | 10 April |
| Cabbage | — | 20 March | sow 10 April |
| Calendula | — | 20 March | sow 10 April |
| Carrot | — | — | sow 10 April |
| Cauliflower | 6 February | 20 March | 10 April |
| Celeriac | 30 January | 17 April | 8 May |
| Celery | 30 January | 17 April | 8 May |
| Celosia | 7 March | 21 April | 12 May |
| Chamomile | — | 20 March | sow 10 April |
| Chayote | 19 January | 17 April | 8 May |
| Chickpea | — | — | sow 10 April |
| Chili Pepper | 5 March | 18 May | 8 June |
| China aster | 16 March | 7 May | 28 May |
| Chives | — | — | sow 10 April |
| Cilantro | — | 20 March | sow 10 April |
| Corn | — | 17 April | sow 8 May |
| Cosmos | 7 March | 21 April | 12 May |
| Cucumber | 26 March | 7 May | 28 May |
| Daikon | — | 20 March | sow 10 April |
| Delphinium | 10 February | — | 10 April |
| Dill | — | 20 March | sow 10 April |
| Eggplant | 26 February | 7 May | 28 May |
| Florence fennel | 3 March | 17 April | 8 May |
| Garden sorrel | — | 20 March | sow 10 April |
| Green Beans | 11 March | 17 April | 8 May |
| Hyssop | — | — | sow 10 April |
| Kale | — | 20 March | sow 10 April |
| Kiwano | 16 March | 17 April | 8 May |
| Kohlrabi | — | 20 March | sow 10 April |
| Leek | 9 January | 20 March | 10 April |
| Lemon balm | — | 20 March | sow 10 April |
| Lettuce | — | 20 March | sow 10 April |
| Lisianthus | 23 December | 20 March | 10 April |
| Lovage | — | — | sow 10 April |
| Luffa | 26 March | 7 May | 28 May |
| Marigold | 6 March | 17 April | 8 May |
| Melon | 16 March | 7 May | 28 May |
| Microgreens | — | 21 April | sow 12 May |
| Moringa | 24 March | 18 May | 8 June |
| Mustard greens | — | 20 March | sow 10 April |
| Napa cabbage | 15 March | 17 April | 8 May |
| Nasturtium | 10 March | 17 April | 8 May |
| Okra | 26 March | 7 May | 28 May |
| Oregano | 19 January | 20 March | 10 April |
| Pansy | 23 January | 20 March | 10 April |
| Parsley | — | 20 March | sow 10 April |
| Parsnip | — | — | sow 10 April |
| Peanut | 31 March | 7 May | 28 May |
| Peas | — | 20 March | sow 10 April |
| Petunia | 5 March | 7 May | 28 May |
| Physalis | 3 March | 17 April | 8 May |
| Pumpkin | 11 March | 17 April | 8 May |
| Purple coneflower | 7 February | — | 10 April |
| Radish | — | — | sow 10 April |
| Sage | 30 January | 20 March | 10 April |
| Snapdragon | 14 January | 20 March | 10 April |
| Spinach | — | 20 March | sow 10 April |
| Stevia | 27 February | 17 April | 8 May |
| Stock | — | 20 March | sow 10 April |
| Sunflower | — | 21 April | sow 12 May |
| Sweet Corn | — | 17 April | sow 8 May |
| Sweet pea | 6 February | 20 March | 10 April |
| Sweet William | — | — | sow 10 April |
| Swiss Chard | — | 20 March | sow 10 April |
| Thyme | — | 20 March | sow 10 April |
| Tomato | 19 February | 17 April | 8 May |
| Turnip | — | 20 March | sow 10 April |
| Watercress | — | 20 March | sow 10 April |
| Watermelon | 5 April | 7 May | 28 May |
| Zinnia | 13 April | 18 May | 8 June |
| 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.
Denver: weather for the next 7 days
Forecast by Open-Meteo. Nights at or below 0 °C are marked as frost.
Weather in Denver by month
Average weather in Denver over 2016–2025: the warmest month is July, the wettest May.
| Month | Day, °C | Night, °C | Rain, mm | Rainy days |
|---|---|---|---|---|
| January | 5.1 | -9 | 23 | 5 |
| February | 6.9 | -8.8 | 26 | 5 |
| March | 12.6 | -3.7 | 51 | 7 |
| April | 17.5 | 0.6 | 43 | 8 |
| May | 21.5 | 6.1 | 87 | 12 |
| June | 29.4 | 12.6 | 44 | 7 |
| July | 32.2 | 16.1 | 30 | 7 |
| August | 30.9 | 15.2 | 39 | 8 |
| September | 28.3 | 11.1 | 23 | 5 |
| October | 19.9 | 3.5 | 26 | 5 |
| November | 12.7 | -2.2 | 18 | 4 |
| December | 8 | -5.4 | 14 | 3 |
Average of the daily highs and lows, rain per month and days with at least 1 mm (ERA5 via Open-Meteo, the same grid cell as the frost dates).
Planted in autumn
| Crop | Plant around |
|---|---|
| Bearded Iris | 15 September |
| Crocus | 15 September |
| Daffodil | 15 September |
| Garlic | 15 September |
| Hyacinth | 15 September |
| Lily | 15 September |
| Peony | 15 September |
| Saffron | 15 September |
| Tulip | 15 September |
| Wild garlic | 15 September |
A month before the first autumn frost, so the roots grow before winter.