Frost dates for 80228Denver, CO
The average last spring frost in Denver is May 3 and the average first fall frost is October 14, giving a typical growing season of about 161 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 3
- Average first fall frost
- Oct 14
- Growing season
- 161 days
Safer after May 17 (1-in-10 risk)
Possible by Sep 30 (1-in-10 risk)
Last frost typically in 188 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 30 · May 12 · May 27 | Sep 20 · Oct 5 · Oct 18 | 143 days | 100% |
| Frost / freeze (32°F) | Apr 21 · May 3 · May 17 | Sep 30 · Oct 14 · Oct 28 | 161 days | 100% |
| Hard freeze (28°F) | Apr 7 · Apr 25 · May 8 | Oct 7 · Oct 23 · Nov 6 | 182 days | 100% |
Planting calendar for Denver
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Apr 2 – Jun 8 |
| Tomatoes | Transplant outdoors | May 19 – Jun 24 |
| Peppers | Start seeds indoors | Apr 2 – May 3 |
| Peppers | Transplant outdoors | Jun 2 – Jul 3 |
| Eggplant | Start seeds indoors | Apr 19 – May 18 |
| Eggplant | Transplant outdoors | Jun 2 – Jul 3 |
| Cucumbers | Sow outdoors | Jun 2 – Jul 4 |
| Summer squash | Sow outdoors | May 19 – Jul 3 |
| Winter squash & pumpkins | Sow outdoors | Jun 2 – Jul 3 |
| Snap beans | Sow outdoors | May 19 – Jul 27 |
| Sweet corn | Sow outdoors | May 19 – Jun 24 |
| Watermelon & cantaloupe | Sow outdoors | Jun 2 – Jul 3 |
| Okra | Sow outdoors | May 26 – Jun 18 |
| Peas | Sow outdoors (spring) | Apr 2 – May 18 |
| Potatoes | Plant outdoors (spring) | Apr 2 – Jun 2 |
| Onions | Start seeds indoors (spring) | Feb 19 – Mar 18 |
| Onions | Transplant outdoors (spring) | Apr 19 – May 18 |
| Broccoli | Start seeds indoors (spring) | Mar 15 – Apr 18 |
| Broccoli | Transplant outdoors (spring) | Apr 19 – May 18 |
| Broccoli | Start seeds indoors (fall) | Jun 14 – Jun 24 |
| Broccoli | Transplant outdoors (fall) | Jul 14 – Jul 25 |
| Cabbage | Start seeds indoors (spring) | Mar 5 – Apr 2 |
| Cabbage | Transplant outdoors (spring) | Apr 2 – May 3 |
| Cabbage | Start seeds indoors (fall) | Jun 4 – Jul 4 |
| Cabbage | Transplant outdoors (fall) | Jul 4 – Aug 4 |
| Leaf lettuce | Sow outdoors (spring) | Apr 2 – Jun 18 |
| Leaf lettuce | Sow outdoors (fall) | Jul 4 – Aug 20 |
| Spinach | Sow outdoors (spring) | Mar 26 – May 9 |
| Spinach | Sow outdoors (fall) | Jul 21 – Aug 25 |
| Radishes | Sow outdoors (spring) | Apr 2 – May 23 |
| Radishes | Sow outdoors (fall) | Jul 4 – Sep 4 |
| Kale | Sow outdoors (spring) | Apr 19 – May 9 |
| Kale | Sow outdoors (fall) | Jun 27 – Aug 4 |
| Carrots | Sow outdoors (spring) | May 3 – Jun 18 |
| Carrots | Sow outdoors (fall) | Jun 4 – Jul 20 |
| Garlic | Plant outdoors (fall) | Oct 4 – Nov 4 |
Where these dates come from
ZIP code 80228 is matched to the NOAA station Ralston Rsvr, CO, 17.1 km away, at 5,900 ft elevation (261 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Ralston Rsvr, CO (used) | 5,900 ft | May 3 | Oct 14 |
| Lakewood, CO | 5,640 ft | May 3 | Oct 7 |
| Wheat Ridge 2, CO | 5,398 ft | May 5 | Oct 5 |
| Marston Fltr Plt, CO | 5,610 ft | May 2 | Oct 11 |
Frost dates near Denver
- Denver, CO 80225 · last May 3, first Oct 7
- Golden, CO 80401 · last May 3, first Oct 14
- Idledale, CO 80453 · last May 23, first Sep 22
- Morrison, CO 80465 · last May 16, first Oct 1
- Littleton, CO 80123 · last May 2, first Oct 11
- Indian Hills, CO 80454 · last May 23, first Sep 22
- Wheat Ridge, CO 80033 · last May 5, first Oct 5
- Kittredge, CO 80457 · last May 23, first Sep 22
Frequently asked questions
- When is the last frost in Denver, CO?
- For ZIP code 80228, the average last spring frost (32°F) is May 3, based on NOAA 1991-2020 climate normals for the Ralston Rsvr, CO weather station. There is a 1-in-10 chance of a frost after May 17.
- When is the first frost in Denver, CO?
- The average first fall frost (32°F) is October 14. There is a 1-in-10 chance of frost by September 30, so tender plants are at risk from that point on.
- How long is the growing season in 80228?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 161 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.