Mickeylee
Watermelon in the US

Watermelon needs warm soil, around 70°F (21°C) or more, so wait until after your last frost date. For zones 3-5, sow seeds from May to July, depending on your specific zone. For zones 6-8, April to June works well, and for zones 9-10, you can start as early as January right through to July. Plant seeds about 1 inch (2.5 cm) deep, either directly where they're to grow or in small pots indoors a few weeks before transplanting. Give them plenty of space, maybe 3-4 feet (90-120 cm) apart, as they love to spread out.

If you started seeds indoors, you'll need to harden them off properly before planting them out. Just a week or so, gradually getting them used to the outdoors. Once all danger of frost is gone and the soil is warm enough, plant your young plants into their final spot. They'll want good room, so give them at least 3 feet (90 cm) between plants, maybe more if you can. You can let them trail on the ground or, if you're short on space, try growing them up a sturdy trellis – just make sure to support the fruit as it gets heavy.