When to plant broccoli 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). Broccoli needs 60–85 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 broccoli in Colorado: the short answer
For a spring planting, plant out Apr 14 – May 1, with seeds started indoors Mar 17 – Mar 31. 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 broccoli in Colorado, step by step
- Start seeds indoors (Mar 17 – Mar 31). Sow seeds ½ inch deep in seed-starting mix under bright light. They take 5-10 days to sprout, fastest in soil around 75°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 18 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (Apr 14 – May 1). Space plants about 18 inches apart in rows 30 inches apart. It tolerates a light frost but not a hard freeze. As a cool-season crop it does best before summer heat arrives in Colorado.
- 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, aphids, flea beetle, cabbage root maggot. Diseases and disorders: clubroot, black rot, downy mildew.
- Harvest (from about Jun 20 – Jul 15). Broccoli takes 60-85 days to reach harvest. Days to maturity counted from transplant. Keep cutting side shoots after the main head for weeks. Spring crop must size up before heat or it buttons.
Figures come from our crop data; dates use Colorado’s average frost dates. More in the full broccoli growing guide.
Broccoli 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 broccoli dates shift with them.
| Zone | Last frost | First frost | Season | Start indoors | Plant broccoli |
|---|---|---|---|---|---|
| Zone 3 | May 15 | Sep 15 | 120 days | Mar 27 – Apr 10 | Apr 24 – May 11 |
| Zone 4 | May 10 | Sep 25 | 135 days | Mar 22 – Apr 5 | Apr 19 – May 6 |
| Zone 5 | Apr 30 | Oct 5 | 160 days | Mar 12 – Mar 26 | Apr 9 – Apr 26 |
| Zone 6 | Apr 15 | Oct 15 | 185 days | Feb 25 – Mar 11 | Mar 25 – Apr 11 |
| Zone 7 | Apr 5 | Oct 25 | 200 days | Feb 15 – Mar 1 | Mar 15 – Apr 1 |
When to plant broccoli in nearby states
Questions gardeners in Colorado ask
When is the best time to plant broccoli in Colorado?
Plant broccoli transplants outdoors in Colorado between April 14 and May 1. 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 broccoli seeds indoors in Colorado?
Start seeds indoors between March 17 and March 31, about 6 weeks before the last frost, so the seedlings are ready to plant out from April 14.
Can I plant broccoli in the fall in Colorado?
Yes. For a fall crop, start transplants between June 22 and July 9, so the crop matures in cool weather before Colorado's first frost around October 1.
When will broccoli planted in Colorado be ready to harvest?
Planted on time, broccoli is usually ready from about June 20 to July 15, 60-85 days after transplanting.
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.