When to plant cucumbers in Colorado
Colorado’s average last spring frost is May 5, and the first fall frost typically arrives around October 1 — about 149 frost-free days (USDA zones 3b, 4b, 5a, 5b, 6a, 7a). Cucumber needs 50–70 days to mature, which fits comfortably within Colorado's growing season.
Colorado 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 Colorado: the short answer
For a spring planting, plant out May 12 – May 29, with seeds started indoors Apr 7 – Apr 21. Wait until the soil is at least 60°F and frost is over.
Succession sow again in Colorado: Jun 9 · Jun 30 · Jul 21
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 Colorado, step by step
- Start seeds indoors (Apr 7 – Apr 21). 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 12 – May 29). 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 8 – Jul 28). 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 Colorado’s average frost dates. More in the full cucumber growing guide.
Cucumber planting dates by USDA zone in Colorado
Colorado spans USDA zones 3b, 4b, 5a, 5b, 6a, 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 Colorado ask
When is the best time to plant cucumbers in Colorado?
Plant cucumber transplants outdoors in Colorado between May 12 and May 29. That timing is set by Colorado's average last spring frost of May 5; Colorado spans several climates, so cooler and higher parts of the state run later.
When should I start cucumber seeds indoors in Colorado?
Start seeds indoors between April 7 and April 21, about 3 weeks before the last frost, so the seedlings are ready to plant out from May 12.
Can I plant cucumbers in the fall in Colorado?
Yes. For a fall crop, sow between June 29 and July 16, so the crop matures in cool weather before Colorado's first frost around October 1.
When will cucumbers planted in Colorado be ready to harvest?
Planted on time, cucumbers are usually ready from about July 8 to July 28, 50-70 days after planting.
When is the last frost in Colorado?
On average around May 5, with the first fall frost around October 1 - about 149 frost-free days. Your town may differ by two weeks or more.