Seedless varieties are triploid. They should be started in the greenhouse and transplanted when soil temperature in the field are 65°F. Seedless watermelons need a pollinator variety planted with them.
Seedless watermelons require special attention. They must be started indoors. Start at the same time as your pollinator variety (packet of sugar baby gratis with your order).
Use very well drained seed starting mix kept at a steady soil temperature of 85°F. Sow seedless watermelons 3 weeks before outside soil reaches 65°F. Seedlings cannot be transplanted until they have 2-3 sets of leaves and their roots have filled the soil in the pot.