yes, in the North there are two solutions to this, one is to do what
Steve in the Adirondacks does (make a trench with hot manure, that will
heat the soil) and the other is to plant the seed under cover
(hoophouse or tunnel). I have myself noticed how much variation there
is in my transplants, some cuke plants start pumping cukes by late
June, and other plants remain small and start fruiting a month later.
Next year I am going to combine both methods, as I will take the plunge
with both watermelons and melons. Thanks for the Yellow Doll tip.