When to Plant Basil in Colorado
Start Seeds Indoors
Monday, February 23, 2026
Transplant outdoors: Monday, May 4, 2026
State
Colorado
USDA Zones
4a, 4b, 5a, 5b, 6a, 6b, 7a
Avg Last Frost
Monday, April 20, 2026
Cities Covered
397
Colorado Planting Schedule by Zone
Colorado spans 7 zones — find yours below for the most accurate dates.
| Zone | Last Frost | Start Indoors | Transplant |
|---|---|---|---|
| 4a | Friday, May 15, 2026 | Friday, March 20, 2026 | Friday, May 29, 2026 |
| 4b | Tuesday, May 5, 2026 | Tuesday, March 10, 2026 | Tuesday, May 19, 2026 |
| 5a | Sunday, May 10, 2026 | Sunday, March 15, 2026 | Sunday, May 24, 2026 |
| 5b | Saturday, April 25, 2026 | Saturday, February 28, 2026 | Saturday, May 9, 2026 |
| 6a | Monday, April 20, 2026 | Monday, February 23, 2026 | Monday, May 4, 2026 |
| 6b | Wednesday, April 15, 2026 | Wednesday, February 18, 2026 | Wednesday, April 29, 2026 |
| 7a | Friday, April 10, 2026 | Friday, February 13, 2026 | Friday, April 24, 2026 |
Dates based on average last frost. Check your local forecast before planting.
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Growing Basil in Colorado: Complete Guide
Basil (Ocimum basilicum) is a warm-season crop that needs a head start indoors before Colorado's last frost. Most Colorado gardeners begin seeds indoors around Monday, February 23, 2026 and move transplants outside around Monday, May 4, 2026, after the risk of frost has passed.
Because Colorado stretches across 7 USDA hardiness zones (4a, 4b, 5a, 5b, 6a, 6b, 7a), planting windows can shift by as much as six to eight weeks from one end of the state to the other. Gardeners in the warmer southern zones can start earlier, while those in cooler northern zones should wait until the zone table above shows their last frost has passed.
With 60 days to maturity, Basil needs the indoor head start that Colorado's growing season requires. Starting indoors ensures you have strong transplants ready the moment outdoor conditions are right.
Basil requires full sun (6-8 hours) and regular (keep moist) moisture. Most of Colorado receives adequate sunlight during the growing season, though gardeners in humid eastern regions should watch for fungal issues and ensure good air circulation.
For the most precise planting dates tailored to your exact location, enter your ZIP code on our planting calendar or use the zone table above to find the schedule for your area of Colorado.
Growing Basil in Colorado: Local Tips
Climate-specific advice for Colorado gardeners.
Start indoors 6 weeks early
Colorado and Utah gardeners lose weeks of basil season to late frosts; start seeds in April and transplant under row cover in late May for a meaningful harvest before fall frost arrives in September.
Frequently Asked Questions
When should I plant Basil in Colorado?
In Colorado, start Basil seeds indoors around Monday, February 23, 2026 and transplant outdoors around Monday, May 4, 2026 after your last frost. Colorado spans zones 4a–7a, so dates shift by 1–4 weeks depending on where you live.
What is the last frost date in Colorado?
Colorado spans 7 USDA zones (4a, 4b, 5a, 5b, 6a, 6b, 7a), so last frost dates vary by region. Hartsel, Gunnison, Craig (4a) sees frost until around Friday, May 15, 2026, while Cortez, Mesa Verde National Park, Towaoc (7a) is frost-free much earlier.
How long does Basil take to grow in Colorado?
Basil takes about 60 days from transplant (or direct sow) to harvest. Starting seeds indoors in Colorado gives you a head start so plants are ready to go out after the last frost.
What USDA zones does Colorado cover for Basil?
Colorado includes zones 4a, 4b, 5a, 5b, 6a, 6b, 7a. Basil grows well across all of these zones with adjusted timing — use the zone table above to find the right dates for your part of the state.
Find Precise Dates for Your City
Select a city for exact planting dates based on local frost records.