When to plant broccoli in Seattle, Washington

February 13 – February 27

Transplant outdoors · typical Seattle year

Climate basis: NOAA station Seattle Boeing Fld, WA (USW00024234), 5 mi (8 km) from downtown Seattle (ZCTA 98104 centroid), elevation 20 ft, on the 1991–2020 climate normals. Transplant broccoli outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (March 13). One year in ten still freezes after April 1.

Last spring freezeMarch 131-in-10 after Apr 1

First fall freezeNovember 171-in-10 before Nov 1

Frost-free season≈ 247 daysmedian at 32°F

Hard freeze, 28°Feb 18 – Dec 2kills even hardy greens

USDA zone9a20 to 25°F winter low — not frost timing

The Seattle year

Start seeds indoorsJan 2 – Jan 16

Transplant outdoorsFeb 13 – Feb 27

Fall plantingSep 22 – Oct 20

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

Broccoli in Seattle · freeze context from Seattle Boeing Fld, WA, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Jan 2 – Jan 16

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 (Mar 13). University of New Hampshire Extension · University of Missouri Extension

Transplant outdoors

Feb 13 – Feb 27

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 (Mar 13). University of New Hampshire Extension · Purdue University Extension

Fall planting

Sep 22 – Oct 20

Purdue Table 2: plant fall broccoli at least 4–8 weeks before the first fall frost. Anchored to the median first fall freeze (Nov 17). Purdue University Extension

Variety assumption: Assumes an average heading variety (about 60–70 days from transplant).

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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