When to plant kohlrabi in Chicago, Illinois

March 13 – March 27

Transplant outdoors · typical Chicago year

Climate basis: NOAA station Chicago Northerly Is, IL (USC00111550), 2 mi (3 km) from downtown Chicago (ZCTA 60602 centroid), elevation 583 ft, on the 1991–2020 climate normals. Transplant kohlrabi outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (April 10). One year in ten still freezes after April 25.

Last spring freezeApril 101-in-10 after Apr 25

First fall freezeNovember 51-in-10 before Oct 24

Frost-free season≈ 208 daysmedian at 32°F

Hard freeze, 28°Apr 1 – Nov 15kills even hardy greens

USDA zone6b-5 to 0°F winter low — not frost timing

The Chicago year

Start seeds indoorsJan 30 – Feb 13

Transplant outdoorsMar 13 – Mar 27

Fall plantingSep 10 – Oct 8

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 25

Kohlrabi in Chicago · freeze context from Chicago Northerly Is, IL, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Jan 30 – Feb 13

Sow 4–6 weeks before the set-out window opens (UNH: time from seed to transplant 4–6 weeks). Anchored to the median last spring freeze (Apr 10). University of New Hampshire Extension

Transplant outdoors

Mar 13 – Mar 27

UNH: safe to set out 4 weeks before the last frost; Purdue's hardy class allows 4–6 weeks before. The later UNH start is used. Anchored to the median last spring freeze (Apr 10). University of New Hampshire Extension · Purdue University Extension

Fall planting

Sep 10 – Oct 8

Purdue Table 2: plant fall kohlrabi at least 4–8 weeks before the first fall frost. Anchored to the median first fall freeze (Nov 5). Purdue University Extension

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 (2)

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.
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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