When to plant kohlrabi in Hartford, Connecticut

March 20 – April 3

Transplant outdoors · typical Hartford year

Climate basis: NOAA station Hartford Brainard Fld, CT (USW00014752), 2 mi (4 km) from downtown Hartford (ZCTA 06103 centroid), elevation 19 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 17). One year in ten still freezes after May 1.

Last spring freezeApril 171-in-10 after May 1

First fall freezeOctober 261-in-10 before Oct 12

Frost-free season≈ 191 daysmedian at 32°F

Hard freeze, 28°Apr 3 – Nov 5kills even hardy greens

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

The Hartford year

Start seeds indoorsFeb 6 – Feb 20

Transplant outdoorsMar 20 – Apr 3

Fall plantingAug 31 – Sep 28

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

Kohlrabi in Hartford · freeze context from Hartford Brainard Fld, CT, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Feb 6 – Feb 20

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 17). University of New Hampshire Extension

Transplant outdoors

Mar 20 – Apr 3

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 17). University of New Hampshire Extension · Purdue University Extension

Fall planting

Aug 31 – Sep 28

Purdue Table 2: plant fall kohlrabi at least 4–8 weeks before the first fall frost. Anchored to the median first fall freeze (Oct 26). 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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