Frost dates for 80023Broomfield, 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 80023 is matched to the NOAA station Northglenn, CO, 7 km away, at 5,407 ft elevation (125 ft higher 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 |
| Brighton 3 Se, CO | 5,016 ft | May 3 | Oct 7 |
| Boulder, CO | 5,484 ft | May 6 | Oct 5 |
| Wheat Ridge 2, CO | 5,398 ft | May 5 | Oct 5 |
Frost dates near Broomfield
- Denver, CO 80234 · last May 2, first Oct 11
- Broomfield, CO 80020 · last May 2, first Oct 11
- Eastlake, CO 80614 · last May 2, first Oct 11
- Lafayette, CO 80026 · last May 2, first Oct 11
- Brighton, CO 80602 · last May 3, first Oct 7
- Westminster, CO 80031 · last May 2, first Oct 11
- Thornton, CO 80241 · last May 2, first Oct 11
- Louisville, CO 80027 · last May 6, first Oct 5
Frequently asked questions
- When is the last frost in Broomfield, CO?
- For ZIP code 80023, 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 80023?
- 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.