Colorado planting calendar

When to plant cauliflower in Colorado — sow, transplant & harvest dates

Colorado is mostly USDA zone 5b (range 3b-7a). Dates below are derived from cauliflower's frost tolerance and Colorado's frost window — not generic national averages.

Cauliflower planting timetable for Colorado

Stage	When in Colorado	Anchor
Start seeds indoors	early April (April 3)	6 weeks before the last frost (mid-May)
Transplant outside	early May (May 1)	14 days before the last frost (mid-May)
First harvest (estimate)	late July (July 25)	~85 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Colorado's climate shifts the cauliflower dates

Colorado's last spring frost averages mid-May and first fall frost late September, which sets the whole planting clock. Colorado gardening is shaped by altitude, intense sun, low humidity, and big day-night temperature swings. Frost can come in any month at high elevation. Sow early — cauliflower bolt once daytime temperatures hold above 24 °C, so the earlier they go in, the longer the harvest.

More temperature-sensitive than broccoli — optimal growing range is 15–18 °C (60–65 °F); temperatures above 27 °C (80 °F) cause loose, ricey curds, while a sharp frost below −3 °C (27 °F) can damage developing heads. Start indoors 6–8 weeks before last frost and transplant 2–3 weeks before last frost. Blanch white varieties by tying outer leaves over the curd when it reaches golf-ball size, or choose self-blanching types. Succession planting is difficult in spring in hot climates (zones 7+); fall crops from a midsummer sowing are often more reliable.

Frost-risk note

Don't plant before mid-May — a hard freeze can still set young plants back. In the high Rockies and mountain valleys (zone 3b-4b) the safe date runs a week or two later.

Regional variation within Colorado

the high Rockies and mountain valleys (zone 3b-4b) runs roughly 1-2 weeks behind the state average; the western slope around Grand Junction (zone 7a) can plant 1-2 weeks earlier.

Denver — USDA zone 6a
Colorado Springs — USDA zone 6a
Boulder — USDA zone 6a
Grand Junction — USDA zone 7a
Fort Collins — USDA zone 5b

What else to plant in Colorado around then

The same early window suits peas, lettuce, spinach, and onion sets.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 7–24 °C (45–75 °F).
Spacing: 18–24 inches (45–60 cm) between plants.
Days to harvest: ~85 days from planting out.

Frequently asked questions

When is the best time to plant cauliflower in Colorado?

In Colorado (mostly USDA zone 5b), sow cauliflower indoors around early April, transplant outdoors early May (before the last frost, mid-May), and harvest from late July. Cauliflower are half-hardy — young plants shrug off a light frost but not a hard freeze, so sowing can start a couple of weeks before the last spring frost.

What USDA zone is Colorado?

Most of Colorado sits in USDA hardiness zone 5b, with the state spanning roughly 3b-7a from the high Rockies and mountain valleys (zone 3b-4b) to the western slope around Grand Junction (zone 7a). The last spring frost averages mid-May and the first fall frost late September.

Can you grow cauliflower in Colorado?

Yes. Colorado's dominant zone 5b supports cauliflower — the key is timing. Cauliflower are half-hardy — young plants shrug off a light frost but not a hard freeze, so sowing can start a couple of weeks before the last spring frost.

Does the planting date change across Colorado?

the high Rockies and mountain valleys (zone 3b-4b) runs roughly 1-2 weeks behind the state average; the western slope around Grand Junction (zone 7a) can plant 1-2 weeks earlier.

What else can I plant in Colorado around the same time?

The same early window suits peas, lettuce, spinach, and onion sets.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.