When to plant celery in Philadelphia, Pennsylvania

March 30 – April 13

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 celery 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 5 – Jan 19

Transplant outdoorsMar 30 – Apr 13

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

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

Every method, with its sources

Start seeds indoors

Jan 5 – Jan 19

Sow 10–12 weeks before the set-out window opens (UNH: time from seed to transplant 10–12 weeks). Anchored to the median last spring freeze (Mar 30). University of New Hampshire Extension

Transplant outdoors

Mar 30 – Apr 13

UNH: set out after the last frost. Purdue's semi-hardy class allows 2–4 weeks before; the later UNH rule is used (celery is easily vernalized by cold spells). Anchored to the median last spring freeze (Mar 30). University of New Hampshire Extension · Purdue University Extension

Variety assumption: A long, steady season (about 100–120 days from transplant; Penn State lists 120).

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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