Windsor, CO planting zone & frost dates
Windsor is in USDA hardiness zone 5b. The last spring frost usually comes around May 3 and the first fall frost around October 6, for a growing season of about 154 days.
Planting calendar for Windsor
Dates are counted from the average last spring frost (May 3) 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 8 – Mar 22 Transplant outdoors: May 10 – May 17 |
| Peppers | Start seeds indoors: Feb 22 – Mar 8 Transplant outdoors: May 17 – May 24 |
| Eggplant | Start seeds indoors: Feb 22 – Mar 8 Transplant outdoors: May 17 – May 24 |
| Broccoli | Start seeds indoors: Feb 22 – Mar 8 Transplant outdoors: Apr 5 – Apr 19 |
| Cabbage | Start seeds indoors: Feb 22 – Mar 8 Transplant outdoors: Apr 5 – Apr 19 |
| Onions (sets) | Plant outdoors: Apr 5 – Apr 19 |
| Peas | Sow outdoors: Mar 22 – Apr 5 |
| Spinach | Sow outdoors: Mar 22 – Apr 5 |
| Lettuce | Sow outdoors: Apr 5 – Apr 19 |
| Carrots | Sow outdoors: Apr 5 – Apr 19 |
| Potatoes | Plant outdoors: Apr 5 – Apr 19 |
| Beans | Sow outdoors: May 10 – May 17 |
| Sweet corn | Sow outdoors: May 10 – May 17 |
| Cucumbers | Sow outdoors: May 10 – May 17 |
| Squash & zucchini | Sow outdoors: May 10 – May 17 |
| Basil | Start seeds indoors: Mar 22 – Apr 5 Transplant outdoors: May 10 – May 17 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 11 (8 weeks before the average first fall frost on Oct 6).
Useful for zone 5b gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
- Cold frame / mini greenhouse — adds weeks to a short season
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Apr 21 | May 3 | May 15 |
| First 32°F frost in fall is before | Oct 17 | Oct 6 | Sep 22 |
How to read it: in spring there is a 10% chance of a frost after May 15, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 22. A hard freeze (28°F) usually ends around April 23.
Hardiness zone by ZIP code in Windsor
- 80550 zone 5b
- 80551 zone 5b
Nearby cities
Questions
What growing zone is Windsor, CO?
Windsor 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 Windsor?
The average last spring frost (32°F) in Windsor is May 3. There is still a 10% chance of frost until May 15.
When can I plant tomatoes in Windsor?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 10 – May 17. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Ft Collins 4 E, CO (USC00053006), 15.0 km (9.3 mi) from the city center, elevation 1500 m, based on 29 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.