Frost dates for 80021Broomfield, CO
The average last spring frost in Broomfield is May 2 and the average first fall frost is October 11, giving a typical growing season of about 160 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 2
- Average first fall frost
- Oct 11
- Growing season
- 160 days
Safer after May 14 (1-in-10 risk)
Possible by Sep 26 (1-in-10 risk)
Last frost typically in 180 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 26 | Sep 18 · Oct 1 · Oct 14 | 142 days | 100% |
| Frost / freeze (32°F) | Apr 18 · May 2 · May 14 | Sep 26 · Oct 11 · Oct 24 | 160 days | 100% |
| Hard freeze (28°F) | Apr 4 · Apr 20 · May 5 | Oct 7 · Oct 21 · Nov 4 | 182 days | 100% |
Planting calendar for Broomfield
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 1 – Jun 7 |
| Tomatoes | Transplant outdoors | May 18 – Jun 21 |
| Peppers | Start seeds indoors | Apr 1 – May 2 |
| Peppers | Transplant outdoors | Jun 1 – Jul 2 |
| Eggplant | Start seeds indoors | Apr 18 – May 17 |
| Eggplant | Transplant outdoors | Jun 1 – Jul 2 |
| Cucumbers | Sow outdoors | Jun 1 – Jul 1 |
| Summer squash | Sow outdoors | May 18 – Jul 2 |
| Winter squash & pumpkins | Sow outdoors | Jun 1 – Jul 2 |
| Snap beans | Sow outdoors | May 18 – Jul 24 |
| Sweet corn | Sow outdoors | May 18 – Jun 21 |
| Watermelon & cantaloupe | Sow outdoors | Jun 1 – Jul 2 |
| Okra | Sow outdoors | May 25 – Jun 17 |
| Peas | Sow outdoors (spring) | Apr 1 – May 17 |
| Potatoes | Plant outdoors (spring) | Apr 1 – Jun 1 |
| Onions | Start seeds indoors (spring) | Feb 18 – Mar 17 |
| Onions | Transplant outdoors (spring) | Apr 18 – May 17 |
| Broccoli | Start seeds indoors (spring) | Mar 14 – Apr 17 |
| Broccoli | Transplant outdoors (spring) | Apr 18 – May 17 |
| Broccoli | Start seeds indoors (fall) | Jun 11 – Jun 21 |
| Broccoli | Transplant outdoors (fall) | Jul 11 – Jul 22 |
| Cabbage | Start seeds indoors (spring) | Mar 4 – Apr 1 |
| Cabbage | Transplant outdoors (spring) | Apr 1 – May 2 |
| Cabbage | Start seeds indoors (fall) | Jun 1 – Jul 1 |
| Cabbage | Transplant outdoors (fall) | Jul 1 – Aug 1 |
| Leaf lettuce | Sow outdoors (spring) | Apr 1 – Jun 17 |
| Leaf lettuce | Sow outdoors (fall) | Jul 1 – Aug 17 |
| Spinach | Sow outdoors (spring) | Mar 25 – May 8 |
| Spinach | Sow outdoors (fall) | Jul 18 – Aug 22 |
| Radishes | Sow outdoors (spring) | Apr 1 – May 22 |
| Radishes | Sow outdoors (fall) | Jul 1 – Sep 1 |
| Kale | Sow outdoors (spring) | Apr 18 – May 8 |
| Kale | Sow outdoors (fall) | Jun 24 – Aug 1 |
| Carrots | Sow outdoors (spring) | May 2 – Jun 17 |
| Carrots | Sow outdoors (fall) | Jun 1 – Jul 17 |
| Garlic | Plant outdoors (fall) | Oct 1 – Nov 1 |
Where these dates come from
ZIP code 80021 is matched to the NOAA station Northglenn, CO, 8.7 km away, at 5,407 ft elevation (55 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Northglenn, CO (used) | 5,407 ft | May 2 | Oct 11 |
| Ralston Rsvr, CO | 5,900 ft | May 3 | Oct 14 |
| Wheat Ridge 2, CO | 5,398 ft | May 5 | Oct 5 |
| Lakewood, CO | 5,640 ft | May 3 | Oct 7 |
Frost dates near Broomfield
- Broomfield, CO 80038 · last May 2, first Oct 11
- Arvada, CO 80005 · last May 3, first Oct 7
- Westminster, CO 80031 · last May 2, first Oct 11
- Denver, CO 80234 · last May 2, first Oct 11
- Louisville, CO 80027 · last May 6, first Oct 5
- Thornton, CO 80241 · last May 2, first Oct 11
- Wheat Ridge, CO 80033 · last May 5, first Oct 5
- Lafayette, CO 80026 · last May 2, first Oct 11
Frequently asked questions
- When is the last frost in Broomfield, CO?
- For ZIP code 80021, the average last spring frost (32°F) is May 2, based on NOAA 1991-2020 climate normals for the Northglenn, CO weather station. There is a 1-in-10 chance of a frost after May 14.
- When is the first frost in Broomfield, CO?
- The average first fall frost (32°F) is October 11. There is a 1-in-10 chance of frost by September 26, so tender plants are at risk from that point on.
- How long is the growing season in 80021?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 160 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.