When to plant zucchini / summer squash 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). Zucchini / Summer Squash needs 45–60 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 zucchini / summer squash in Colorado: the short answer
For a spring planting, plant out May 5 – May 22, 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 · Jul 7
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 zucchini / summer squash 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 5-10 days to sprout, fastest in soil around 85°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 14 inches deep, with a pH between 5.5 and 7.5. Dig in compost before planting.
- Plant out (May 5 – May 22). Space plants about 30 inches apart in rows 42 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: squash vine borer, squash bug, striped cucumber beetle, aphids. Diseases and disorders: powdery mildew, bacterial wilt, blossom-end rot (calcium disorder).
- Harvest (from about Jun 26 – Jul 11). Zucchini / Summer Squash takes 45-60 days to reach harvest. One or two plants feed a household. A second sowing in early-mid summer dodges the first vine borer generation.
Figures come from our crop data; dates use Colorado’s average frost dates. More in the full zucchini / summer squash growing guide.
Zucchini 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 zucchini / summer squash dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant zucchini / summer squash |
|---|---|---|---|---|---|
| Zone 3 | May 15 | Sep 15 | 120 days | Apr 17 – May 1 | May 15 – Jun 1 |
| Zone 4 | May 10 | Sep 25 | 135 days | Apr 12 – Apr 26 | May 10 – May 27 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | Apr 2 – Apr 16 | Apr 30 – May 17 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | Mar 18 – Apr 1 | Apr 15 – May 2 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | Mar 8 – Mar 22 | Apr 5 – Apr 22 |
When to plant zucchini / summer squash in nearby states
Questions gardeners in Colorado ask
When is the best time to plant zucchini / summer squash in Colorado?
Plant zucchini / summer squash transplants outdoors in Colorado between May 5 and May 22. 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 zucchini / summer squash 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 5.
Can I plant zucchini / summer squash 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 zucchini / summer squash planted in Colorado be ready to harvest?
Planted on time, zucchini / summer squash is usually ready from about June 26 to July 11, 45-60 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.