GreenlyWhen to plant watermelon in Philadelphia
In Philadelphia, watermelon: sow seedlings around 22 March for the greenhouse and around 12 April for open ground; plant into a greenhouse around 23 April; plant out into open ground around 14 May.
Last spring frost around 3 April, first autumn frost around 11 November. Frost-free days: 222 days.
The dates follow the Greenly calendar: open ground a week after the last frost once the soil is warm enough for the crop, frost-hardy crops three weeks before it, an unheated greenhouse three weeks earlier, seedlings sown so they are ready on the day. In a cold year allow a week or two more.