When to plant winter squash in Sioux Falls, South Dakota
May 15 – May 29
Transplant outdoors · typical Sioux Falls yearClimate basis: NOAA station Sioux Falls, SD (USW00014944), 2 mi (3 km) from downtown Sioux Falls (ZCTA 57104 centroid), elevation 1430 ft, on the 1991–2020 climate normals. Transplant winter squash outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 1). One year in ten still freezes after May 14.
The Sioux Falls year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to May 14
Every method, with its sources
Start seeds indoors
Apr 17 – Apr 24Sow in pots 3–4 weeks before the outdoor window opens (UNH 3–4 weeks; Missouri G6570 3–5 weeks). Anchored to the median last spring freeze (May 1). University of New Hampshire Extension · University of Missouri Extension
Transplant outdoors
May 15 – May 29UNH: set out 2 weeks after last frost; Purdue very-tender class agrees. Anchored to the median last spring freeze (May 1). University of New Hampshire Extension · Purdue University Extension
Direct-sow outdoors
May 15 – May 29Purdue: very tender — at least two weeks after the average last frost; Penn State earliest sowing May 15 (+14 days) agrees. Anchored to the median last spring freeze (May 1). Purdue University Extension · Penn State Extension (York County Master Gardeners)
Variety assumption: Assumes an average butternut/acorn-type variety (about 90–110 days; Penn State lists 90). Fruit must mature before fall frost.
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 (4)
- University of New Hampshire Extension: Growing Vegetables: When to Plant Your Vegetable Garden [fact sheet] (accessed 2026-07-24)Per-crop 'time from seed to transplant' and 'safe to set out in garden' relative to last frost.
- University of Missouri Extension: Starting Plants Indoors from Seeds (G6570) (accessed 2026-07-24)Weeks needed to grow vegetable transplants indoors (Table 2).
- 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.
- 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.