Red, juicy watermelons are a welcome snack after a long, hot day. Growing these sweet fruits in your garden requires proper planting and fertilization as they grow to maturity. Watermelons are warm-season plants, so they must be seeded outdoors only when there is no longer a danger of frost. You can also purchase seedlings and transplant these to the garden for an earlier harvest. These large vine plants take up a lot of room in the garden, but the sweet reward at harvest time makes it well worthwhile.
Add a 4-inch layer of compost over a well-drained, full-sun garden bed. Apply 4 cups of 10-10-10 analysis fertilizer per each 100 square feet of bed, then till the compost and fertilizer into the top 6 to 8 inches of soil.
Sow watermelon seeds 1 to 2 inches deep when soil temperatures reach 65 F. Space the seeds 2 feet apart in rows that are 4 feet apart. Alternately, plant seedlings at the same spacing, sowing them at the same depth as they were growing in their nursery pots.
Water the bed immediately after planting until it feels moist at a 6-inch depth when you stick your finger into it. Apply a 2- to 4-inch layer of straw mulch to the garden to preserve soil moisture once soil temperatures reach 75 F. Water once weekly thereafter, moistening the bed to the 6-inch depth at each irrigation.
Fertilize a second time when the vines begin growing runners, or additional vines that spread across the garden. Apply 1 to 2 tbsp. of high-nitrogen 32-0-0 analysis fertilizer per plant. Work the fertilizer into the soil 6 inches from the watermelon plant. Fertilize a third time in the same manner when the vines begin producing flowers.
Harvest watermelon when the fruits are firm and the skin becomes dull. The curly vines around the watermelon stem will be brown and dry once fruit is completely ripe.