When to plant brussels sprouts in Des Moines, Iowa

March 21 – April 4

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 brussels sprouts 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 indoorsFeb 7 – Feb 21

Transplant outdoorsMar 21 – Apr 4

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

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

Every method, with its sources

Start seeds indoors

Feb 7 – Feb 21

Sow 4–6 weeks before the set-out window opens (UNH 4–6 weeks; Missouri G6570 6–8 weeks). Anchored to the median last spring freeze (Apr 18). University of New Hampshire Extension · University of Missouri Extension

Transplant outdoors

Mar 21 – Apr 4

UNH: set out 2–4 weeks before the last frost; Purdue's hardy class allows 4–6 weeks before. The later UNH range is used. Anchored to the median last spring freeze (Apr 18). University of New Hampshire Extension · Purdue University Extension

Variety assumption: A long-season crop (about 90–110 days from transplant); sprouts sweeten after light fall frosts.

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 (3)

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.

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