When to plant kohlrabi in Boston, Massachusetts

March 7 – March 21

Transplant outdoors · typical Boston year

Climate basis: NOAA station Boston Logan INTL AP, MA (USW00014739), 3 mi (5 km) from downtown Boston (ZCTA 02108 centroid), elevation 12 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 4). One year in ten still freezes after April 17.

Last spring freezeApril 41-in-10 after Apr 17

First fall freezeNovember 91-in-10 before Oct 29

Frost-free season≈ 218 daysmedian at 32°F

Hard freeze, 28°Mar 28 – Nov 21kills even hardy greens

USDA zone7a0 to 5°F winter low — not frost timing

The Boston year

Start seeds indoorsJan 24 – Feb 7

Transplant outdoorsMar 7 – Mar 21

Fall plantingSep 14 – Oct 12

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 17

Kohlrabi in Boston · freeze context from Boston Logan INTL AP, MA, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Jan 24 – Feb 7

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 4). University of New Hampshire Extension

Transplant outdoors

Mar 7 – Mar 21

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

Fall planting

Sep 14 – Oct 12

Purdue Table 2: plant fall kohlrabi at least 4–8 weeks before the first fall frost. Anchored to the median first fall freeze (Nov 9). 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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