When to plant tomatoes in Colorado
Colorado’s average last spring frost is May 5, and the first fall frost typically arrives around October 1 — about 149 frost-free days (USDA zones 3b, 4b, 5a, 5b, 6a, 7a). Tomato needs 60–85 days to mature, which fits comfortably within Colorado's growing season.
Colorado covers a wide range of climates, so your exact frost dates may differ from the state average by two weeks or more. For dates tuned to your town, use the calendar generator.
When to plant tomatoes in Colorado: the short answer
For a spring planting, plant out May 5 – May 22, with seeds started indoors Mar 10 – Mar 24. Wait until the soil is at least 50°F and frost is over.
Windows are ~1–2 week bands around each date. Frost dates are a statewide average from NOAA/NCEI normals; your town may differ by two weeks or more. Calendar year 2026.
How to grow tomatoes in Colorado, step by step
- Start seeds indoors (Mar 10 – Mar 24). Sow seeds ¼ inch deep in seed-starting mix under bright light. They take 5-10 days to sprout, fastest in soil around 80°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. They need at least six to eight hours of direct sun a day and loose soil at least 18 inches deep, with a pH between 5.5 and 7.5. Dig in compost before planting.
- Plant out (May 5 – May 22). Space plants about 24 inches apart in rows 36 inches apart. It is killed by frost, so nothing goes outside until the danger has passed.
- Water and feed. Give it steady, even moisture, about an inch of water a week from rain or the hose.
- Watch for pests and problems. Pests: tomato hornworm, aphids, whitefly, flea beetle. Diseases and disorders: early blight, late blight, septoria leaf spot, fusarium wilt, blossom-end rot (calcium disorder).
- Harvest (from about Jul 11 – Aug 5). Tomato takes 60-85 days to reach harvest. Days to maturity counted from transplant. Bury 2/3 of the stem at transplanting for extra roots. Determinate types suit containers and one big harvest; indeterminate types need staking and produce until frost.
Figures come from our crop data; dates use Colorado’s average frost dates. More in the full tomato growing guide.
Tomato planting dates by USDA zone in Colorado
Colorado spans USDA zones 3b, 4b, 5a, 5b, 6a, 7a. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average, so the tomato dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant tomato |
|---|---|---|---|---|---|
| Zone 3 | May 15 | Sep 15 | 120 days | Mar 20 – Apr 3 | May 15 – Jun 1 |
| Zone 4 | May 10 | Sep 25 | 135 days | Mar 15 – Mar 29 | May 10 – May 27 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | Mar 5 – Mar 19 | Apr 30 – May 17 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | Feb 18 – Mar 4 | Apr 15 – May 2 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | Feb 8 – Feb 22 | Apr 5 – Apr 22 |
When to plant tomatoes in nearby states
Questions gardeners in Colorado ask
When is the best time to plant tomatoes in Colorado?
Plant tomato transplants outdoors in Colorado between May 5 and May 22. That timing is set by Colorado's average last spring frost of May 5; Colorado spans several climates, so cooler and higher parts of the state run later.
When should I start tomato seeds indoors in Colorado?
Start seeds indoors between March 10 and March 24, about 7 weeks before the last frost, so the seedlings are ready to plant out from May 5.
What is the latest I can plant tomatoes in Colorado?
About August 2. Tomatoes need at least 60 days to mature after transplanting, and frost around October 1 ends the season, so later plantings risk being cut short.
When will tomatoes planted in Colorado be ready to harvest?
Planted on time, tomatoes are usually ready from about July 11 to August 5, 60-85 days after transplanting.
When is the last frost in Colorado?
On average around May 5, with the first fall frost around October 1 - about 149 frost-free days. Your town may differ by two weeks or more.