When to plant cucumbers 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). Cucumber needs 50–70 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 cucumbers in Idaho: the short answer
For a spring planting, plant out May 17 – Jun 3, with seeds started indoors Apr 12 – Apr 26. Wait until the soil is at least 60°F and frost is over.
Succession sow again in Idaho: Jun 14 · Jul 5
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 cucumbers in Idaho, step by step
- Start seeds indoors (Apr 12 – Apr 26). Sow seeds 1 inch deep in seed-starting mix under bright light. They take 3-10 days to sprout, fastest in soil around 85°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 14 inches deep, with a pH between 5.5 and 7.0. Dig in compost before planting.
- Plant out (May 17 – Jun 3). Space plants about 12 inches apart in rows 48 inches apart. It is killed by frost, so nothing goes outside until the danger has passed.
- Water and feed. It needs plenty of water; keep the soil evenly moist and never let it dry out.
- Watch for pests and problems. Pests: striped cucumber beetle, squash bug, aphids, spider mite. Diseases and disorders: powdery mildew, downy mildew, bacterial wilt, angular leaf spot.
- Harvest (from about Jul 13 – Aug 2). Cucumber takes 50-70 days to reach harvest. Resents root disturbance - if starting indoors use peat/paper pots. Trellising doubles the plants per square foot and cuts disease. A second sowing in midsummer beats early beetle pressure.
Figures come from our crop data; dates use Idaho’s average frost dates. More in the full cucumber growing guide.
Cucumber 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 cucumber dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant cucumber |
|---|---|---|---|---|---|
| Zone 3 | May 15 | Sep 15 | 120 days | Apr 17 – May 1 | May 22 – Jun 8 |
| Zone 4 | May 10 | Sep 25 | 135 days | Apr 12 – Apr 26 | May 17 – Jun 3 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | Apr 2 – Apr 16 | May 7 – May 24 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | Mar 18 – Apr 1 | Apr 22 – May 9 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | Mar 8 – Mar 22 | Apr 12 – Apr 29 |
When to plant cucumbers in nearby states
Questions gardeners in Idaho ask
When is the best time to plant cucumbers in Idaho?
Plant cucumber 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 cucumber seeds indoors in Idaho?
Start seeds indoors between April 12 and April 26, about 3 weeks before the last frost, so the seedlings are ready to plant out from May 17.
Can I plant cucumbers in the fall in Idaho?
Yes. For a fall crop, sow between June 23 and July 10, so the crop matures in cool weather before Idaho's first frost around September 25.
When will cucumbers planted in Idaho be ready to harvest?
Planted on time, cucumbers are usually ready from about July 13 to August 2, 50-70 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.