When to plant winter squash in St. Louis, Missouri

April 15 – April 29

Transplant outdoors · typical St. Louis year

Climate basis: NOAA station St Louis Sci Ctr, MO (USC00237452), 4 mi (7 km) from downtown St. Louis (ZCTA 63101 centroid), elevation 515 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 (April 1). One year in ten still freezes after April 18.

Last spring freezeApril 11-in-10 after Apr 18

First fall freezeNovember 41-in-10 before Oct 24

Frost-free season≈ 218 daysmedian at 32°F

Hard freeze, 28°Mar 22 – Nov 15kills even hardy greens

USDA zone7a0 to 5°F winter low — not frost timing

The St. Louis year

Start seeds indoorsMar 18 – Mar 25

Transplant outdoorsApr 15 – Apr 29

Direct-sow outdoorsApr 15 – Apr 29

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 18

Winter squash in St. Louis · freeze context from St Louis Sci Ctr, MO, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Mar 18 – Mar 25

Sow 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 (Apr 1). University of New Hampshire Extension · University of Missouri Extension

Transplant outdoors

Apr 15 – Apr 29

UNH: set out 2 weeks after last frost; Purdue very-tender class agrees. Anchored to the median last spring freeze (Apr 1). University of New Hampshire Extension · Purdue University Extension

Direct-sow outdoors

Apr 15 – Apr 29

Purdue: 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 (Apr 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.

This week, not a typical year:

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.

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