When to plant kohlrabi in Grand Rapids, Michigan

April 8 – April 22

Transplant outdoors · typical Grand Rapids year

Climate basis: NOAA station E Grand Rapids, MI (USC00202375), 3 mi (5 km) from downtown Grand Rapids (ZCTA 49503 centroid), elevation 746 ft, on the 1991–2020 climate normals. Transplant kohlrabi outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 6). One year in ten still freezes after May 23.

Last spring freezeMay 61-in-10 after May 23

First fall freezeOctober 101-in-10 before Sep 29

Frost-free season≈ 157 daysmedian at 32°F

Hard freeze, 28°Apr 27 – Oct 23kills even hardy greens

USDA zone6a-10 to -5°F winter low — not frost timing

The Grand Rapids year

Start seeds indoorsFeb 25 – Mar 11

Transplant outdoorsApr 8 – Apr 22

Fall plantingAug 15 – Sep 12

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to May 23

Kohlrabi in Grand Rapids · freeze context from E Grand Rapids, MI, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Feb 25 – Mar 11

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 (May 6). University of New Hampshire Extension

Transplant outdoors

Apr 8 – Apr 22

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 (May 6). University of New Hampshire Extension · Purdue University Extension

Fall planting

Aug 15 – Sep 12

Purdue Table 2: plant fall kohlrabi at least 4–8 weeks before the first fall frost. Anchored to the median first fall freeze (Oct 10). 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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