When to plant kohlrabi in Philadelphia, Pennsylvania

March 2 – March 16

Transplant outdoors · typical Philadelphia year

Climate basis: NOAA station Phila Franklin Inst, PA (USC00366886), 1 mi (1 km) from downtown Philadelphia (ZCTA 19107 centroid), elevation 60 ft, on the 1991–2020 climate normals. Transplant kohlrabi outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (March 30). One year in ten still freezes after April 12.

Last spring freezeMarch 301-in-10 after Apr 12

First fall freezeNovember 171-in-10 before Nov 4

Frost-free season≈ 232 daysmedian at 32°F

Hard freeze, 28°Mar 17 – Nov 29kills even hardy greens

USDA zone7b5 to 10°F winter low — not frost timing

The Philadelphia year

Start seeds indoorsJan 19 – Feb 2

Transplant outdoorsMar 2 – Mar 16

Fall plantingSep 22 – Oct 20

indoors under lights
in the garden
frost-free season
1-in-10 years still freeze to Apr 12

Kohlrabi in Philadelphia · freeze context from Phila Franklin Inst, PA, 1991–2020 normals.

Every method, with its sources

Start seeds indoors

Jan 19 – Feb 2

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 (Mar 30). University of New Hampshire Extension

Transplant outdoors

Mar 2 – Mar 16

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 (Mar 30). University of New Hampshire Extension · Purdue University Extension

Fall planting

Sep 22 – Oct 20

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