When to plant basil in Philadelphia, Pennsylvania
April 13 – April 29
Transplant outdoors · typical Philadelphia yearClimate 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 basil 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.
The Philadelphia year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to Apr 12
Every method, with its sources
Start seeds indoors
Feb 23 – Mar 2Iowa State: start seeds indoors 4 or 5 weeks before the last frost date. Anchored to the median last spring freeze (Mar 30). Iowa State University Extension and Outreach
Transplant outdoors
Apr 13 – Apr 29UNH: set out 2 weeks after the last frost; Oklahoma State: plant one month after the last spring frost; Iowa State: after all danger of frost. The window spans the UNH and Oklahoma State recommendations. Anchored to the median last spring freeze (Mar 30). University of New Hampshire Extension · Oklahoma State University Extension · Iowa State University Extension and Outreach
Direct-sow outdoors
Apr 29 – May 13Oklahoma State Table 1 times basil planting one month after the last spring frost; Iowa State adds direct sowing once nights stay above 50°F. Point rule given a 14-day span. Anchored to the median last spring freeze (Mar 30). Oklahoma State University Extension · Iowa State University Extension and Outreach
Variety assumption: Leaves are harvestable about 30–40 days after transplanting.
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.
Crop rule sources (3)
- Iowa State University Extension and Outreach: Growing Basil in the Home Garden (accessed 2026-07-24)"Start seeds indoors 4 or 5 weeks before the last frost date." "Plant basil outdoors after all danger of frost is past."
- 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.
- Oklahoma State University Extension: Culinary Herbs for Oklahoma Gardens: Culture, Use and Preservation (accessed 2026-07-24)Table 1 planting times relative to last spring frost for common herbs.