When to plant tomatoes in Idaho
Idaho’s average last spring frost is May 10, and the first fall frost typically arrives around September 25 — about 138 frost-free days (USDA zones 3b, 4b, 5b, 6a, 6b, 7a). Tomato needs 60–85 days to mature, which fits comfortably within Idaho's growing season.
Idaho 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 Idaho: the short answer
For a spring planting, plant out May 10 – May 27, with seeds started indoors Mar 15 – Mar 29. 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 Idaho, step by step
- Start seeds indoors (Mar 15 – Mar 29). 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 10 – May 27). 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 16 – Aug 10). 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 Idaho’s average frost dates. More in the full tomato growing guide.
Tomato planting dates by USDA zone in Idaho
Idaho spans USDA zones 3b, 4b, 5b, 6a, 6b, 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 Idaho ask
When is the best time to plant tomatoes in Idaho?
Plant tomato transplants outdoors in Idaho between May 10 and May 27. That timing is set by Idaho's average last spring frost of May 10; Idaho spans several climates, so cooler and higher parts of the state run later.
When should I start tomato seeds indoors in Idaho?
Start seeds indoors between March 15 and March 29, about 7 weeks before the last frost, so the seedlings are ready to plant out from May 10.
What is the latest I can plant tomatoes in Idaho?
About July 27. Tomatoes need at least 60 days to mature after transplanting, and frost around September 25 ends the season, so later plantings risk being cut short.
When will tomatoes planted in Idaho be ready to harvest?
Planted on time, tomatoes are usually ready from about July 16 to August 10, 60-85 days after transplanting.
When is the last frost in Idaho?
On average around May 10, with the first fall frost around September 25 - about 138 frost-free days. Your town may differ by two weeks or more.