GreenlyWhen to plant watermelon in Belfast
In Belfast, watermelon: sow seedlings around 15 May for the greenhouse and around 5 June for open ground; plant into a greenhouse around 16 June; plant out into open ground around 7 July.
Last spring frost around 18 April, first autumn frost around 19 November. Frost-free days: 215 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.