When to plant winter squash in Des Moines, Iowa

May 2 – May 16

Transplant outdoors · typical Des Moines year

Climate basis: NOAA station Des Moines INTL AP, IA (USW00014933), 4 mi (6 km) from downtown Des Moines (ZCTA 50309 centroid), elevation 957 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 18). One year in ten still freezes after May 2.

Last spring freezeApril 181-in-10 after May 2

First fall freezeOctober 201-in-10 before Oct 4

Frost-free season≈ 184 daysmedian at 32°F

Hard freeze, 28°Apr 8 – Oct 30kills even hardy greens

USDA zone5b-15 to -10°F winter low — not frost timing

The Des Moines year

Start seeds indoorsApr 4 – Apr 11

Transplant outdoorsMay 2 – May 16

Direct-sow outdoorsMay 2 – May 16

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 2

Winter squash in Des Moines · freeze context from Des Moines INTL AP, IA, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Apr 4 – Apr 11

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 18). University of New Hampshire Extension · University of Missouri Extension

Transplant outdoors

May 2 – May 16

UNH: set out 2 weeks after last frost; Purdue very-tender class agrees. Anchored to the median last spring freeze (Apr 18). University of New Hampshire Extension · Purdue University Extension

Direct-sow outdoors

May 2 – May 16

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 18). 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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