USDA Hardiness Zone 6a
Frost Dates for 80209 — Denver, Colorado
Averages from Denver Water Dept, Co US, the nearest reporting station, 2.7 miles away.
Plant tender crops after April 30, and expect the first autumn freeze around October 12. That leaves about 165 frost-free days.
- Last spring frost
- April 30
- First fall frost
- October 12
- Growing season
- 165 days
- Hardiness zone
- 6a
50% probability
50% probability
frost-free
-10 to -5°F annual low
Planting calendar for 80209
| When | What to do |
|---|---|
| February 19 – March 5 | Start peppers and aubergines indoors They need eight to ten weeks under lights before they can go out. |
| March 5 – March 19 | Start tomatoes indoors Six to eight weeks gives a transplant big enough to set fruit early. |
| April 2 – April 16 | Sow peas, spinach, lettuce, radish outdoors These tolerate light frost and prefer to germinate in cool soil. |
| April 30 onward | Transplant tomatoes, peppers, basil, squash, cucumbers The average last freeze has passed — still watch the actual forecast. |
| by July 20 | Sow the autumn crop of carrots, beets and brassicas They need about twelve weeks to size up before growth stops. |
| by September 28 | Harvest tender crops, or be ready to cover them A first freeze two weeks early is well within normal variation. |
| October 12 onward | Plant garlic, mulch beds, lift tender bulbs Garlic wants a cold spell; bare soil loses structure over winter. |
What these dates mean
Wait until after April 30 to put tender plants — tomatoes, peppers, basil, squash — in the ground. That is the date by which half of years in Denver, Colorado are past their last freeze. Harvest before October 12, which leaves roughly 165 frost-free days.
ZIP 80209 sits in USDA hardiness zone 6a, meaning the average coldest night of the year falls between -10 to -5°F. Zone decides what survives the winter; frost dates decide when to plant each spring. They are different questions, and a plant can pass one and fail the other.
These are thirty-year NOAA averages for 1991–2020, not a forecast. Any individual year can frost two to three weeks either side of these dates, so check the actual forecast before planting out.