Johnstown, CO planting zone & frost dates
Johnstown is in USDA hardiness zone 5b. The last spring frost usually comes around May 10 and the first fall frost around October 1, for a growing season of about 142 days.
Planting calendar for Johnstown
Dates are counted from the average last spring frost (May 10) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Mar 15 – Mar 29 Transplant outdoors: May 17 – May 24 |
| Peppers | Start seeds indoors: Mar 1 – Mar 15 Transplant outdoors: May 24 – May 31 |
| Eggplant | Start seeds indoors: Mar 1 – Mar 15 Transplant outdoors: May 24 – May 31 |
| Broccoli | Start seeds indoors: Mar 1 – Mar 15 Transplant outdoors: Apr 12 – Apr 26 |
| Cabbage | Start seeds indoors: Mar 1 – Mar 15 Transplant outdoors: Apr 12 – Apr 26 |
| Onions (sets) | Plant outdoors: Apr 12 – Apr 26 |
| Peas | Sow outdoors: Mar 29 – Apr 12 |
| Spinach | Sow outdoors: Mar 29 – Apr 12 |
| Lettuce | Sow outdoors: Apr 12 – Apr 26 |
| Carrots | Sow outdoors: Apr 12 – Apr 26 |
| Potatoes | Plant outdoors: Apr 12 – Apr 26 |
| Beans | Sow outdoors: May 17 – May 24 |
| Sweet corn | Sow outdoors: May 17 – May 24 |
| Cucumbers | Sow outdoors: May 17 – May 24 |
| Squash & zucchini | Sow outdoors: May 17 – May 24 |
| Basil | Start seeds indoors: Mar 29 – Apr 12 Transplant outdoors: May 17 – May 24 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 6 (8 weeks before the average first fall frost on Oct 1).
Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 30 | May 10 | May 22 |
| First 32°F frost in fall is before | Oct 13 | Oct 1 | Sep 15 |
How to read it: in spring there is a 10% chance of a frost after May 22, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 15. A hard freeze (28°F) usually ends around May 2.
Hardiness zone by ZIP code in Johnstown
- 80534 zone 5b
Nearby cities
Questions
What growing zone is Johnstown, CO?
Johnstown is in USDA Plant Hardiness Zone 5b (average extreme winter low -15°F to -10°F), according to the USDA 2023 map.
When is the last frost in Johnstown?
The average last spring frost (32°F) in Johnstown is May 10. There is still a 10% chance of frost until May 22.
When can I plant tomatoes in Johnstown?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 17 – May 24. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Loveland 2N, CO (USC00055236), 18.3 km (11.4 mi) from the city center, elevation 1548 m, based on 25 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.