Frost dates for 81638Hamilton, CO
The average last spring frost in Hamilton is May 29 and the average first fall frost is September 20, giving a typical growing season of about 113 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 29
- Average first fall frost
- Sep 20
- Growing season
- 113 days
Safer after Jun 13 (1-in-10 risk)
Possible by Sep 5 (1-in-10 risk)
Last frost typically in 214 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 30 · Jun 12 · Jun 30 | Aug 31 · Sep 11 · Sep 23 | 91 days | 100% |
| Frost / freeze (32°F) | May 13 · May 29 · Jun 13 | Sep 5 · Sep 20 · Oct 3 | 113 days | 100% |
| Hard freeze (28°F) | Apr 29 · May 13 · Jun 1 | Sep 15 · Sep 30 · Oct 13 | 138 days | 100% |
Planting calendar for Hamilton
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 28 – Jul 4 |
| Tomatoes | Transplant outdoors | Jun 14 – May 31 |
| Peppers | Start seeds indoors | Apr 28 – May 29 |
| Peppers | Transplant outdoors | Jun 28 – Jul 29 |
| Eggplant | Start seeds indoors | May 15 – Jun 13 |
| Eggplant | Transplant outdoors | Jun 28 – Jul 29 |
| Cucumbers | Sow outdoors | Jun 28 – Jun 10 |
| Summer squash | Sow outdoors | Jun 14 – Jul 29 |
| Winter squash & pumpkins | Sow outdoors | Jun 28 – Jul 29 |
| Snap beans | Sow outdoors | Jun 14 – Jul 3 |
| Sweet corn | Sow outdoors | Jun 14 – May 31 |
| Watermelon & cantaloupe | Sow outdoors | Jun 28 – Jul 29 |
| Okra | Sow outdoors | Jun 21 – Jul 14 |
| Peas | Sow outdoors (spring) | Apr 28 – Jun 13 |
| Potatoes | Plant outdoors (spring) | Apr 28 – Jun 28 |
| Onions | Start seeds indoors (spring) | Mar 17 – Apr 13 |
| Onions | Transplant outdoors (spring) | May 15 – Jun 13 |
| Broccoli | Start seeds indoors (spring) | Apr 10 – May 14 |
| Broccoli | Transplant outdoors (spring) | May 15 – Jun 13 |
| Broccoli | Start seeds indoors (fall) | May 21 – May 31 |
| Broccoli | Transplant outdoors (fall) | Jun 20 – Jul 1 |
| Cabbage | Start seeds indoors (spring) | Mar 31 – Apr 28 |
| Cabbage | Transplant outdoors (spring) | Apr 28 – May 29 |
| Cabbage | Start seeds indoors (fall) | May 11 – Jun 10 |
| Cabbage | Transplant outdoors (fall) | Jun 10 – Jul 11 |
| Leaf lettuce | Sow outdoors (spring) | Apr 28 – Jul 14 |
| Leaf lettuce | Sow outdoors (fall) | Jun 10 – Jul 27 |
| Spinach | Sow outdoors (spring) | Apr 21 – Jun 4 |
| Spinach | Sow outdoors (fall) | Jun 27 – Aug 1 |
| Radishes | Sow outdoors (spring) | Apr 28 – Jun 18 |
| Radishes | Sow outdoors (fall) | Jun 10 – Aug 11 |
| Kale | Sow outdoors (spring) | May 15 – Jun 4 |
| Kale | Sow outdoors (fall) | Jun 3 – Jul 11 |
| Carrots | Sow outdoors (spring) | May 29 – Jul 14 |
| Carrots | Sow outdoors (fall) | May 11 – Jun 26 |
| Garlic | Plant outdoors (fall) | Sep 10 – Oct 11 |
Where these dates come from
ZIP code 81638 is matched to the NOAA station Craig 4Sw, CO, 14.1 km away, at 6,496 ft elevation (912 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Craig 4Sw, CO (used) | 6,496 ft | May 29 | Sep 20 |
| Craig Moffat Co Ap, CO | 6,186 ft | Jun 6 | Sep 12 |
| Hayden, CO | 6,467 ft | Jun 1 | Sep 20 |
| Meeker Ap, CO | 6,390 ft | May 30 | Sep 22 |
Frost dates near Hamilton
- Craig, CO 81626 · last Jun 6, first Sep 12
- Hayden, CO 81639 · last Jun 1, first Sep 20
- Meeker, CO 81641 · last Jun 4, first Sep 16
- Phippsburg, CO 80469 · last Jun 14, first Sep 11
- Oak Creek, CO 80467 · last Jun 14, first Sep 11
- Yampa, CO 80483 · last Jun 14, first Sep 11
- Steamboat Springs, CO 80487 · last Jun 9, first Sep 12
- Dinosaur, CO 81633 · last May 10, first Oct 4
Frequently asked questions
- When is the last frost in Hamilton, CO?
- For ZIP code 81638, the average last spring frost (32°F) is May 29, based on NOAA 1991-2020 climate normals for the Craig 4Sw, CO weather station. There is a 1-in-10 chance of a frost after June 13.
- When is the first frost in Hamilton, CO?
- The average first fall frost (32°F) is September 20. There is a 1-in-10 chance of frost by September 5, so tender plants are at risk from that point on.
- How long is the growing season in 81638?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 113 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.