Frost dates for 80534Johnstown, CO
The average last spring frost in Johnstown is May 7 and the average first fall frost is October 5, giving a typical growing season of about 151 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- May 7
- Average first fall frost
- Oct 5
- Growing season
- 151 days
Safer after May 22 (1-in-10 risk)
Possible by Sep 23 (1-in-10 risk)
Last frost typically in 192 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 5 · May 18 · Jun 2 | Sep 14 · Sep 28 · Oct 8 | 132 days | 100% |
| Frost / freeze (32°F) | Apr 24 · May 7 · May 22 | Sep 23 · Oct 5 · Oct 16 | 151 days | 100% |
| Hard freeze (28°F) | Apr 11 · Apr 28 · May 12 | Sep 30 · Oct 12 · Oct 25 | 169 days | 100% |
Planting calendar for Johnstown
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 6 – Jun 12 |
| Tomatoes | Transplant outdoors | May 23 – Jun 15 |
| Peppers | Start seeds indoors | Apr 6 – May 7 |
| Peppers | Transplant outdoors | Jun 6 – Jul 7 |
| Eggplant | Start seeds indoors | Apr 23 – May 22 |
| Eggplant | Transplant outdoors | Jun 6 – Jul 7 |
| Cucumbers | Sow outdoors | Jun 6 – Jun 25 |
| Summer squash | Sow outdoors | May 23 – Jul 7 |
| Winter squash & pumpkins | Sow outdoors | Jun 6 – Jul 7 |
| Snap beans | Sow outdoors | May 23 – Jul 18 |
| Sweet corn | Sow outdoors | May 23 – Jun 15 |
| Watermelon & cantaloupe | Sow outdoors | Jun 6 – Jul 7 |
| Okra | Sow outdoors | May 30 – Jun 22 |
| Peas | Sow outdoors (spring) | Apr 6 – May 22 |
| Potatoes | Plant outdoors (spring) | Apr 6 – Jun 6 |
| Onions | Start seeds indoors (spring) | Feb 23 – Mar 22 |
| Onions | Transplant outdoors (spring) | Apr 23 – May 22 |
| Broccoli | Start seeds indoors (spring) | Mar 19 – Apr 22 |
| Broccoli | Transplant outdoors (spring) | Apr 23 – May 22 |
| Broccoli | Start seeds indoors (fall) | Jun 5 – Jun 15 |
| Broccoli | Transplant outdoors (fall) | Jul 5 – Jul 16 |
| Cabbage | Start seeds indoors (spring) | Mar 9 – Apr 6 |
| Cabbage | Transplant outdoors (spring) | Apr 6 – May 7 |
| Cabbage | Start seeds indoors (fall) | May 26 – Jun 25 |
| Cabbage | Transplant outdoors (fall) | Jun 25 – Jul 26 |
| Leaf lettuce | Sow outdoors (spring) | Apr 6 – Jun 22 |
| Leaf lettuce | Sow outdoors (fall) | Jun 25 – Aug 11 |
| Spinach | Sow outdoors (spring) | Mar 30 – May 13 |
| Spinach | Sow outdoors (fall) | Jul 12 – Aug 16 |
| Radishes | Sow outdoors (spring) | Apr 6 – May 27 |
| Radishes | Sow outdoors (fall) | Jun 25 – Aug 26 |
| Kale | Sow outdoors (spring) | Apr 23 – May 13 |
| Kale | Sow outdoors (fall) | Jun 18 – Jul 26 |
| Carrots | Sow outdoors (spring) | May 7 – Jun 22 |
| Carrots | Sow outdoors (fall) | May 26 – Jul 11 |
| Garlic | Plant outdoors (fall) | Sep 25 – Oct 26 |
Where these dates come from
ZIP code 80534 is matched to the NOAA station Longmont 2 Ese, CO, 22.6 km away, at 4,950 ft elevation (75 ft higher than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Longmont 2 Ese, CO (used) | 4,950 ft | May 7 | Oct 5 |
| Loveland 2N, CO | 5,080 ft | May 10 | Oct 1 |
| Greeley Unc, CO | 4,715 ft | May 2 | Oct 8 |
| Waterdale, CO | 5,230 ft | May 12 | Oct 1 |
Frost dates near Johnstown
- Milliken, CO 80543 · last May 2, first Oct 8
- Mead, CO 80542 · last May 7, first Oct 5
- Gilcrest, CO 80623 · last May 2, first Oct 8
- Greeley, CO 80632 · last May 2, first Oct 8
- Loveland, CO 80539 · last May 10, first Oct 1
- Windsor, CO 80551 · last May 3, first Oct 6
- Berthoud, CO 80513 · last May 10, first Oct 1
- La Salle, CO 80645 · last May 2, first Oct 8
Frequently asked questions
- When is the last frost in Johnstown, CO?
- For ZIP code 80534, the average last spring frost (32°F) is May 7, based on NOAA 1991-2020 climate normals for the Longmont 2 Ese, CO weather station. There is a 1-in-10 chance of a frost after May 22.
- When is the first frost in Johnstown, CO?
- The average first fall frost (32°F) is October 5. There is a 1-in-10 chance of frost by September 23, so tender plants are at risk from that point on.
- How long is the growing season in 80534?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 151 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.