Welby, CO planting zone & frost dates
Welby is in USDA hardiness zone 6a. The last spring frost usually comes around May 2 and the first fall frost around October 11, for a growing season of about 160 days.
Planting calendar for Welby
Dates are counted from the average last spring frost (May 2) 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 7 – Mar 21 Transplant outdoors: May 9 – May 16 |
| Peppers | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: May 16 – May 23 |
| Eggplant | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: May 16 – May 23 |
| Broccoli | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: Apr 4 – Apr 18 |
| Cabbage | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: Apr 4 – Apr 18 |
| Onions (sets) | Plant outdoors: Apr 4 – Apr 18 |
| Peas | Sow outdoors: Mar 21 – Apr 4 |
| Spinach | Sow outdoors: Mar 21 – Apr 4 |
| Lettuce | Sow outdoors: Apr 4 – Apr 18 |
| Carrots | Sow outdoors: Apr 4 – Apr 18 |
| Potatoes | Plant outdoors: Apr 4 – Apr 18 |
| Beans | Sow outdoors: May 9 – May 16 |
| Sweet corn | Sow outdoors: May 9 – May 16 |
| Cucumbers | Sow outdoors: May 9 – May 16 |
| Squash & zucchini | Sow outdoors: May 9 – May 16 |
| Basil | Start seeds indoors: Mar 21 – Apr 4 Transplant outdoors: May 9 – May 16 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 16 (8 weeks before the average first fall frost on Oct 11).
Useful for zone 6a 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 18 | May 2 | May 14 |
| First 32°F frost in fall is before | Oct 24 | Oct 11 | Sep 26 |
How to read it: in spring there is a 10% chance of a frost after May 14, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 26. A hard freeze (28°F) usually ends around April 20.
Nearby cities
- Thornton zone 6a, last frost May 2
- Commerce City zone 6a, last frost May 4
- Federal Heights zone 6a, last frost May 2
- Sherrelwood zone 6a, last frost May 2
- Northglenn zone 6a, last frost May 2
- Berkley zone 6a, last frost May 5
- Westminster zone 6a, last frost May 2
- Denver zone 6a, last frost Apr 30
Questions
What growing zone is Welby, CO?
Welby is in USDA Plant Hardiness Zone 6a (average extreme winter low -10°F to -5°F), according to the USDA 2023 map.
When is the last frost in Welby?
The average last spring frost (32°F) in Welby is May 2. There is still a 10% chance of frost until May 14.
When can I plant tomatoes in Welby?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 9 – May 16. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Northglenn, CO (USC00055984), 8.3 km (5.2 mi) from the city center, elevation 1648 m, based on 26 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.