Seedless watermelons have been available to home gardeners for more than 40 years. They are the same size and have the same flavor as regular (seeded) watermelons, just without all the seeds. The only problem with seedless watermelons is that they don't produce enough pollen to guarantee fruit development. Planting seeded watermelons as pollinators will help seedless watermelon plants produce outstanding watermelons. Both seedless and seeded watermelon plants and seeds are planted the same way. Just choose seedless and seeded varieties with the same number of days to harvest so their flowers will open at the same time.
Choose a spot in full sun with a soil pH between 6.0 and 8.0. Prepare the planting area 2 to 3 weeks before you want to plant seedless watermelons.
Spread 3 to 4 inches of compost over the planting bed. Sprinkle bone meal and green sand or granite dust over the compost. Mix into the top 6 inches of soil using a garden tiller or shovel.
Rake the bed smooth. Break up soil clumps and remove rocks, roots and other debris.
Spread black plastic mulch over the planting bed. Anchor it with bricks, old boards or loose soil.
Wait until soil temperatures are above 60 degrees F and air temperatures are reliably staying above 55 degrees F.
Use the sharp knife to openings of 12 inches by 12 inches in the black plastic. Space the holes 4 to 6 feet apart for vining seedless watermelons and 2 to 3 feet apart for bush varieties.
Dig holes in each opening. The holes should be 12 inches wide and long and 12 inches deep. Place the soil to one side.
Mix the removed soil with an equal amount of well-rotted manure or compost. Refill the holes with this mix. You should have a 4-to-6-inch mound protruding from the openings in the black fabric mulch.
Sow three watermelon seeds per mound. The seeds should be equidistant from each other and placed toward the edges of the mound. Plant the seeds 1/2 to 3/4 inch deep. Every third mound should be planted with regular watermelon seeds.
Water the seeds well. Allow the top 1/2 to 1 inch of soil to dry slightly before watering again. Depending on the variety, seeds should germinate in 7 to 14 days.
Choose and prepare the planting site as you would if you were planting seedless watermelon seeds.
Select seedless watermelon and regular watermelon seedlings with two to four leaves. Do not use watermelon seedlings that are producing tendrils or flowers or have more than four leaves. These seedlings will have trouble forming the root system needed for optimum fruit production.
Plant two seedless watermelon seedlings per mound. Make holes on opposite sides of the mound and just large enough to accommodate the root systems. Plant at the same level they were growing in their containers. Every third mound should be planted with regular watermelon seedlings.
Give the seedlings 1 to 2 inches of water after planting.