Watermelon is much favored in the summer garden for its juicy red fruit. Watermelon does not take well to root disturbance, even as a seedling. Yet it also does not tolerate frost and needs a long growing season to mature. To grow it in areas with short summers, the answer is to start it inside and later transplant outdoors with minimal root disturbance. Start watermelons in peat pots made from compressed peat that can be planted directly in the garden, minimizing root disturbance.
Fill individual peat pots with quality seed-starting soil. Fill with soil to within 3/4 inch of the rim.
Sow two watermelon seeds in the center of each peat pot. Sow to a depth that's twice the seed's width, about 1 inch deep for most watermelon varieties.
Fill a pan with warm water and set the peat pots inside to absorb the water, making sure the water only fills the pot halfway. Remove the peat pots from the water and place them in a drip tray once the surface of the soil is moist, approximately 30 minutes.
Cover the pots in plastic wrap and set in a warm room (70 to 75 degree Fahrenheit) to germinate. Germination takes between seven and 14 days on average.
Remove the plastic wrap once seedlings emerge, and move the pots to a sunny windowsill or place under grow lights. Position grow lights so they maintain a distance of three inches above the plants.
Thin each pot down to one seedling once the second set of leaves appear. Cut the weakest seedling off at soil level using sharp scissors and leave the strongest seedling in the pot.
Transplant seedlings outside two weeks after all danger of frost has passed and the ground has warmed to at least 65 degrees. Cut off the bottom of the peat pot with a sharp knife and plant deep enough that the rim of the pot is just beneath the soil surface.