When to plant basil 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). Basil needs 30–60 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 basil in Montana: the short answer
For a spring planting, plant out May 22 – Jun 8, with seeds started indoors Apr 3 – Apr 17. Wait until the soil is at least 65°F and frost is over.
Succession sow again in Montana: Jun 19 · Jul 10 · Jul 31
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 basil in Montana, step by step
- Start seeds indoors (Apr 3 – Apr 17). Sow seeds ⅛ 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. It needs at least six to eight hours of direct sun a day and loose soil at least 10 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (May 22 – Jun 8). Space plants about 10 inches apart in rows 12 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: aphids, Japanese beetle, slugs. Diseases and disorders: basil downy mildew, fusarium wilt, damping off.
- Harvest (from about Jun 28 – Jul 28). Basil takes 30-60 days to reach harvest. Cold soil stalls it - wait for warm nights. Pinch above a leaf pair every couple of weeks and remove flower buds to keep leaves coming. Downy mildew-resistant varieties are worth seeking out.
Figures come from our crop data; dates use Montana’s average frost dates. More in the full basil growing guide.
Basil 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 basil dates shift with them.
When to plant basil in nearby states
Questions gardeners in Montana ask
When is the best time to plant basil in Montana?
Plant basil transplants outdoors in Montana between May 22 and June 8. 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 basil seeds indoors in Montana?
Start seeds indoors between April 3 and April 17, about 5 weeks before the last frost, so the seedlings are ready to plant out from May 22.
What is the latest I can plant basil in Montana?
About August 16. Basil needs at least 30 days to mature, and frost around September 15 ends the season, so later plantings risk being cut short.
When will basil planted in Montana be ready to harvest?
Planted on time, basil is usually ready from about June 28 to July 28, 30-60 days after planting.
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.