When to plant basil 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). Basil needs 30–60 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 basil in Idaho: the short answer
For a spring planting, plant out May 17 – Jun 3, with seeds started indoors Mar 29 – Apr 12. Wait until the soil is at least 65°F and frost is over.
Succession sow again in Idaho: Jun 14 · Jul 5 · Jul 26
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 Idaho, step by step
- Start seeds indoors (Mar 29 – Apr 12). 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 17 – Jun 3). 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 23 – Jul 23). 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 Idaho’s average frost dates. More in the full basil growing guide.
Basil 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 basil dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant basil |
|---|---|---|---|---|---|
| Zone 3 | May 15 | Sep 15 | 120 days | Apr 3 – Apr 17 | May 22 – Jun 8 |
| Zone 4 | May 10 | Sep 25 | 135 days | Mar 29 – Apr 12 | May 17 – Jun 3 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | Mar 19 – Apr 2 | May 7 – May 24 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | Mar 4 – Mar 18 | Apr 22 – May 9 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | Feb 22 – Mar 8 | Apr 12 – Apr 29 |
When to plant basil in nearby states
Questions gardeners in Idaho ask
When is the best time to plant basil in Idaho?
Plant basil transplants outdoors in Idaho between May 17 and June 3. 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 basil seeds indoors in Idaho?
Start seeds indoors between March 29 and April 12, about 5 weeks before the last frost, so the seedlings are ready to plant out from May 17.
What is the latest I can plant basil in Idaho?
About August 26. Basil needs at least 30 days to mature, and frost around September 25 ends the season, so later plantings risk being cut short.
When will basil planted in Idaho be ready to harvest?
Planted on time, basil is usually ready from about June 23 to July 23, 30-60 days after planting.
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.