When to plant pumpkins in Denver, Colorado
May 20 – June 3
Transplant outdoors · typical Denver yearClimate basis: NOAA station Denver Water Dept, CO (USC00052223), 2 mi (3 km) from downtown Denver (ZCTA 80202 centroid), elevation 5228 ft, on the 1991–2020 climate normals. Transplant pumpkins outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (April 30). One year in ten still freezes after May 13.
The Denver year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to May 13
Every method, with its sources
Start seeds indoors
Apr 8 – Apr 22Sow in pots 4–6 weeks before the outdoor window opens (Missouri G6570: 4–6 weeks). Anchored to the median last spring freeze (Apr 30). University of Missouri Extension
Transplant outdoors
May 20 – Jun 3Same outdoor timing as direct seeding, using pot-grown transplants. Anchored to the median last spring freeze (Apr 30). Penn State Extension (York County Master Gardeners) · Purdue University Extension · University of Missouri Extension
Direct-sow outdoors
May 20 – Jun 3Purdue: very tender — at least two weeks after the last frost; Penn State's earliest sowing May 21 (+20 days) is the later start and is used. Anchored to the median last spring freeze (Apr 30). Penn State Extension (York County Master Gardeners) · Purdue University Extension
Variety assumption: Assumes an average carving variety (about 100–115 days; Penn State lists 110). For Halloween pumpkins, sow toward the start of the window.
These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.
Crop rule sources (3)
- University of Missouri Extension: Starting Plants Indoors from Seeds (G6570) (accessed 2026-07-24)Weeks needed to grow vegetable transplants indoors (Table 2).
- Penn State Extension (York County Master Gardeners): Vegetable Seed Planting Guide (accessed 2026-07-24)Earliest/latest sowing dates for a May 1 last-frost / Oct 1 first-frost baseline; offsets derived by date difference from May 1. Also days-to-maturity figures.
- Purdue University Extension: Indiana Vegetable Planting Calendar (HO-186-W) (accessed 2026-07-24)Hardiness classes: hardy = plant 4-6 wk before last spring frost; semi-hardy = 2-4 wk before; tender = after average last frost; very tender = at least 2 wk after. Table 2: fall planting at least 4-8 wk before first fall frost.