Brighton, CO planting zone & frost dates
Brighton is in USDA hardiness zone 5b. The last spring frost usually comes around May 3 and the first fall frost around October 7, for a growing season of about 155 days.
Planting calendar for Brighton
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 12 (8 weeks before the average first fall frost on Oct 7).
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 22 | May 3 | May 16 |
| First 32°F frost in fall is before | Oct 19 | Oct 7 | Sep 26 |
How to read it: in spring there is a 10% chance of a frost after May 16, 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 23.
Hardiness zone by ZIP code in Brighton
- 80601 zone 5b
- 80602 zone 6a
- 80603 zone 5b
Nearby cities
- Frederick zone 5b, last frost May 7
- Firestone zone 5b, last frost May 7
- Thornton zone 6a, last frost May 2
- Northglenn zone 6a, last frost May 2
- Welby 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
Questions
What growing zone is Brighton, CO?
Brighton is in USDA Plant Hardiness Zone 5b (average extreme winter low -15°F to -10°F), according to the USDA 2023 map. Some ZIP codes of the city fall in zone 6a.
When is the last frost in Brighton?
The average last spring frost (32°F) in Brighton is May 3. There is still a 10% chance of frost until May 16.
When can I plant tomatoes in Brighton?
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 Brighton 3 Se, CO (USC00050950), 4.8 km (3.0 mi) from the city center, elevation 1529 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.