Colorado planting calendar

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

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

Pumpkins planting timetable for Colorado

Stage	When in Colorado	Anchor
Start seeds indoors	late April (April 24)	3 weeks before the last frost (mid-May)
Transplant outside	late May (May 29)	14 days after the last frost (mid-May)
First harvest (estimate)	early September (September 6)	~100 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 pumpkins 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. Wait for warm soil — pumpkins stall in cold ground even after the air warms, so don't rush them out.

Pumpkins need a long frost-free window — count back from your first fall frost date to confirm 90-120 days are available before sowing. Soil must be at least 18 °C (65 °F) at planting depth; seeds germinate fastest at 21-32 °C. In zone 3-4 where seasons are tight, starting indoors 2-3 weeks early in large pots avoids root disturbance. Zones 9-11 can direct-sow in late July for a fall crop.

Frost-risk note

Don't plant before mid-May — even a light frost will kill seedlings overnight. 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

Pair the post-frost slot with other warm-season crops — peppers, beans, squash, and cucumbers.

Quick-grow guide

Sun: Full sun — 6-8 hours direct.
Soil temperature for germination: 21-32 °C (70-90 °F).
Spacing: 60-84 inches (150-215 cm) for vining types; 36-48 inches (90-120 cm) for bush types between plants.
Days to harvest: ~100 days from planting out.

Frequently asked questions

When is the best time to plant pumpkins in Colorado?

In Colorado (mostly USDA zone 5b), sow pumpkins indoors around late April, transplant outdoors late May (after the last frost, mid-May), and harvest from early September. Pumpkins are frost-tender — a single light frost kills seedlings, so they only go outside once frost danger has fully passed and the soil is warm.

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 pumpkins in Colorado?

Yes. Colorado's dominant zone 5b supports pumpkins — the key is timing. Pumpkins are frost-tender — a single light frost kills seedlings, so they only go outside once frost danger has fully passed and the soil is warm.

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?

Pair the post-frost slot with other warm-season crops — peppers, beans, squash, and cucumbers.

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.