When to plant kale 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). Kale needs 50–65 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 kale in Idaho: the short answer
For a spring planting, plant out Apr 12 – Apr 29, with seeds started indoors Mar 22 – Apr 5. Seeds germinate in soil from 45 to 85°F.
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 kale in Idaho, step by step
- Start seeds indoors (Mar 22 – Apr 5). Sow seeds ½ inch deep in seed-starting mix under bright light. They take 5-10 days to sprout, fastest in soil around 70°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. It needs six or more hours of sun for the best growth, though four to six hours in partial shade is enough and loose soil at least 18 inches deep, with a pH between 6.0 and 7.5. Dig in compost before planting.
- Plant out (Apr 12 – Apr 29). Space plants about 16 inches apart in rows 20 inches apart. It tolerates hard frost, so it is one of the first crops to plant. As a cool-season crop it does best before summer heat arrives in Idaho.
- 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: cabbage worm, cabbage looper, cabbage aphid, flea beetle, harlequin bug. Diseases and disorders: black rot, clubroot, downy mildew.
- Harvest (from about Jun 8 – Jun 23). Kale takes 50-65 days to reach harvest. Flavour turns sweet after a hard frost, so the fall crop is the good one. Pick lower leaves and let the plant keep growing upward.
Figures come from our crop data; dates use Idaho’s average frost dates. More in the full kale growing guide.
Kale 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 kale dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant kale |
|---|---|---|---|---|---|
| Zone 3 | May 15 | Sep 15 | 120 days | Mar 27 – Apr 10 | Apr 17 – May 4 |
| Zone 4 | May 10 | Sep 25 | 135 days | Mar 22 – Apr 5 | Apr 12 – Apr 29 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | Mar 12 – Mar 26 | Apr 2 – Apr 19 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | Feb 25 – Mar 11 | Mar 18 – Apr 4 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | Feb 15 – Mar 1 | Mar 8 – Mar 25 |
When to plant kale in nearby states
Questions gardeners in Idaho ask
When is the best time to plant kale in Idaho?
Plant kale transplants outdoors in Idaho between April 12 and April 29. 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 kale seeds indoors in Idaho?
Start seeds indoors between March 22 and April 5, about 6 weeks before the last frost, so the seedlings are ready to plant out from April 12.
Can I plant kale in the fall in Idaho?
Yes. For a fall crop, sow between June 30 and July 17, so the crop matures in cool weather before Idaho's first frost around September 25.
When will kale planted in Idaho be ready to harvest?
Planted on time, kale is usually ready from about June 8 to June 23, 50-65 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.