When to plant tomatoes in Montana
Montana’s average last spring frost is May 15, and the first fall frost typically arrives around September 15 — about 123 frost-free days (USDA zones 3a, 3b, 4a, 4b, 5a, 5b, 6a). Tomato needs 60–85 days to mature, which fits comfortably within Montana's growing season.
Montana 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 Montana: the short answer
For a spring planting, plant out May 15 – Jun 1, with seeds started indoors Mar 20 – Apr 3. 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 Montana, step by step
- Start seeds indoors (Mar 20 – Apr 3). 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 15 – Jun 1). 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 21 – Aug 15). 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 Montana’s average frost dates. More in the full tomato growing guide.
Tomato planting dates by USDA zone in Montana
Montana spans USDA zones 3a, 3b, 4a, 4b, 5a, 5b, 6a. 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.
When to plant tomatoes in nearby states
Questions gardeners in Montana ask
When is the best time to plant tomatoes in Montana?
Plant tomato transplants outdoors in Montana between May 15 and June 1. That timing is set by Montana's average last spring frost of May 15; Montana spans several climates, so cooler and higher parts of the state run later.
When should I start tomato seeds indoors in Montana?
Start seeds indoors between March 20 and April 3, about 7 weeks before the last frost, so the seedlings are ready to plant out from May 15.
What is the latest I can plant tomatoes in Montana?
About July 17. Tomatoes need at least 60 days to mature after transplanting, and frost around September 15 ends the season, so later plantings risk being cut short.
When will tomatoes planted in Montana be ready to harvest?
Planted on time, tomatoes are usually ready from about July 21 to August 15, 60-85 days after transplanting.
When is the last frost in Montana?
On average around May 15, with the first fall frost around September 15 - about 123 frost-free days. Your town may differ by two weeks or more.