Watermelons are a garden treat during the summer. This warm-season melon requires up to three months to reach maturity, so seed is often started indoors to get a head start on the growing season and to ensure there is enough warm weather for the melons to ripen. There are many watermelon varieties available to the home gardener, both seedless and seeded watermelons. Start seeds indoors four weeks before the last expected frost or start them outside once all frost danger is past.
Fill 3-inch diameter peat pots with a well-drained potting soil. Water the soil until the excess drains from the bottom, and then leave the pots to soak in the excess water for four to six hours, allowing the soil to become evenly moist throughout.
Sow one seedless watermelon seed or two seeded seed-types in each pot. Plant the seeds 1 inch deep.
Cover the pots with a plastic bag, which helps maintain the moisture in the soil. Place the pots in an 80 to 85 F room to germinate.
Remove the bags when sprouts appear. Move the pots to a warm, sunny windowsill and water them when the soil surface begins to feel dry.
Prepare the garden bed prior to seeding. Spread a 2-inch layer of compost over the bed and work it into the top 6 inches of soil. Pull soil up into 4-inch high ridges along each row with a hoe, spacing the ridges 6 to 8 feet apart.
Sow three seeds per every 5 feet of row, planting the seeds into the top of the ridge. Plant the seeds to a 1-inch depth.
Water the seed bed after planting. Moisten the soil to a 6-inch depth. Water as needed to maintain the 6 inches of moisture in the soil, usually one to two times a week.
Thin the seedlings once they have sprouted so that they are spaced approximately 5 feet apart along each ridge. Pull out the excess seedlings, leaving the stronger seedlings in place.