When to plant lettuce 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 lettuce 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 26 – Feb 9

Transplant outdoorsMar 2 – Mar 16

Direct-sow outdoorsMar 9 – Mar 23

Fall plantingSep 22 – Oct 20

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

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

Every method, with its sources

Start seeds indoors

Jan 26 – Feb 9

Sow 4–5 weeks before the set-out window opens (UNH 4–5 weeks; Missouri G6570 lists 6–8 weeks for head lettuce). Anchored to the median last spring freeze (Mar 30). University of New Hampshire Extension · University of Missouri Extension

Transplant outdoors

Mar 2 – Mar 16

UNH: safe to set out 3–4 weeks before the last frost. Anchored to the median last spring freeze (Mar 30). University of New Hampshire Extension

Direct-sow outdoors

Mar 9 – Mar 23

Purdue: semi-hardy — 2–4 weeks before the last frost; Penn State's earliest sowing Apr 10 (−21 days) is the later start and is used. Anchored to the median last spring freeze (Mar 30). Penn State Extension (York County Master Gardeners) · Purdue University Extension

Fall planting

Sep 22 – Oct 20

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

Variety assumption: Assumes leaf lettuce (about 45–55 days; head types run longer).

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 (4)

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.
University of Missouri Extension: Starting Plants Indoors from Seeds (G6570) (accessed 2026-07-24)
Weeks needed to grow vegetable transplants indoors (Table 2).
Penn State Extension (York County Master Gardeners): Vegetable Seed Planting Guide (accessed 2026-07-24)
Earliest/latest sowing dates for a May 1 last-frost / Oct 1 first-frost baseline; offsets derived by date difference from May 1. Also days-to-maturity figures.
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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