Watermelon does best when directly sown once soil temperatures reach 70℉. Plant outside 2-3 weeks after your last frost date. Sow 3-4 seeds 1 inch deep, 4-5 feet apart. Water well with seaweed emulsion after planting. Thin to the strongest plant when plants have 3-4 leaves.
If using square foot gardening, plant shorter bush varieties and plan on one plant taking an entire 4×4 foot bed.
The best time to plant in the low desert of Arizona is during the month of March.
In cooler climates, start seeds indoors in 4 inch or larger pots 1 month before planting outside. Watermelon is very frost tender; wait to plant if there is any danger of frost.