Frost dates for 80455Jamestown, CO
The average last spring frost in Jamestown is May 24 and the average first fall frost is September 23, giving a typical growing season of about 120 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 24
- Average first fall frost
- Sep 23
- Growing season
- 120 days
Safer after Jun 10 (1-in-10 risk)
Possible by Sep 9 (1-in-10 risk)
Last frost typically in 209 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) | May 26 · Jun 7 · Jun 23 | Aug 30 · Sep 13 · Sep 24 | 95 days | 100% |
| Frost / freeze (32°F) | May 11 · May 24 · Jun 10 | Sep 9 · Sep 23 · Oct 6 | 120 days | 100% |
| Hard freeze (28°F) | Apr 30 · May 10 · May 27 | Sep 17 · Oct 3 · Oct 17 | 143 days | 100% |
Planting calendar for Jamestown
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 23 – Jun 29 |
| Tomatoes | Transplant outdoors | Jun 9 – Jun 3 |
| Peppers | Start seeds indoors | Apr 23 – May 24 |
| Peppers | Transplant outdoors | Jun 23 – Jul 24 |
| Eggplant | Start seeds indoors | May 10 – Jun 8 |
| Eggplant | Transplant outdoors | Jun 23 – Jul 24 |
| Cucumbers | Sow outdoors | Jun 23 – Jun 13 |
| Summer squash | Sow outdoors | Jun 9 – Jul 24 |
| Winter squash & pumpkins | Sow outdoors | Jun 23 – Jul 24 |
| Snap beans | Sow outdoors | Jun 9 – Jul 6 |
| Sweet corn | Sow outdoors | Jun 9 – Jun 3 |
| Watermelon & cantaloupe | Sow outdoors | Jun 23 – Jul 24 |
| Okra | Sow outdoors | Jun 16 – Jul 9 |
| Peas | Sow outdoors (spring) | Apr 23 – Jun 8 |
| Potatoes | Plant outdoors (spring) | Apr 23 – Jun 23 |
| Onions | Start seeds indoors (spring) | Mar 12 – Apr 8 |
| Onions | Transplant outdoors (spring) | May 10 – Jun 8 |
| Broccoli | Start seeds indoors (spring) | Apr 5 – May 9 |
| Broccoli | Transplant outdoors (spring) | May 10 – Jun 8 |
| Broccoli | Start seeds indoors (fall) | May 24 – Jun 3 |
| Broccoli | Transplant outdoors (fall) | Jun 23 – Jul 4 |
| Cabbage | Start seeds indoors (spring) | Mar 26 – Apr 23 |
| Cabbage | Transplant outdoors (spring) | Apr 23 – May 24 |
| Cabbage | Start seeds indoors (fall) | May 14 – Jun 13 |
| Cabbage | Transplant outdoors (fall) | Jun 13 – Jul 14 |
| Leaf lettuce | Sow outdoors (spring) | Apr 23 – Jul 9 |
| Leaf lettuce | Sow outdoors (fall) | Jun 13 – Jul 30 |
| Spinach | Sow outdoors (spring) | Apr 16 – May 30 |
| Spinach | Sow outdoors (fall) | Jun 30 – Aug 4 |
| Radishes | Sow outdoors (spring) | Apr 23 – Jun 13 |
| Radishes | Sow outdoors (fall) | Jun 13 – Aug 14 |
| Kale | Sow outdoors (spring) | May 10 – May 30 |
| Kale | Sow outdoors (fall) | Jun 6 – Jul 14 |
| Carrots | Sow outdoors (spring) | May 24 – Jul 9 |
| Carrots | Sow outdoors (fall) | May 14 – Jun 29 |
| Garlic | Plant outdoors (fall) | Sep 13 – Oct 14 |
Where these dates come from
ZIP code 80455 is matched to the NOAA station Gross Rsvr, CO, 20.2 km away, at 7,971 ft elevation (1,018 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Gross Rsvr, CO (used) | 7,971 ft | May 24 | Sep 23 |
| Boulder 14 W, CO | 9,829 ft | Jun 21 | Sep 2 |
| Allenspark 3Nw, CO | 8,500 ft | Jun 14 | Sep 12 |
| Boulder, CO | 5,484 ft | May 6 | Oct 5 |
Frost dates near Jamestown
- Boulder, CO 80306 · last May 24, first Sep 23
- Ward, CO 80481 · last Jun 5, first Sep 16
- Lyons, CO 80540 · last May 6, first Oct 5
- Hygiene, CO 80533 · last May 7, first Oct 5
- Allenspark, CO 80510 · last Jun 14, first Sep 12
- Nederland, CO 80466 · last May 24, first Sep 23
- Niwot, CO 80544 · last May 7, first Oct 5
- Longmont, CO 80503 · last May 7, first Oct 5
Frequently asked questions
- When is the last frost in Jamestown, CO?
- For ZIP code 80455, the average last spring frost (32°F) is May 24, based on NOAA 1991-2020 climate normals for the Gross Rsvr, CO weather station. There is a 1-in-10 chance of a frost after June 10.
- When is the first frost in Jamestown, CO?
- The average first fall frost (32°F) is September 23. There is a 1-in-10 chance of frost by September 9, so tender plants are at risk from that point on.
- How long is the growing season in 80455?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 120 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.