When you find the pumpkin seed of your dreams, plant each seed in an individual peat pot 4-6 weeks before the last spring frost. If you are going to plant the seeds directly in the ground, you have to wait until the ground warms up, so normally in Zone 4 or 5, that would be after Memorial Day--the seeds will probably rot before they germinate if you try to plant them too soon. I'm digressing. Put your seedlings in a warm sunny location(under lights works too). Cucurbits, of which pumpkins are a family member, do not like to have their roots disturbed, but the peat pots take care of that problem. Once you're sure that the last frost has passed, plant your pumpkin plants 3 to a hill and watch them grow!
When you see the first pumpkin on each plant start to develop, watch the plants for signs of more developing pumpkins and ruthlessly pinch them off! It's OK to leave the male flowers, but if you really want super giants, ya gotta get rid of the competition. And do yourself a favor--plant some little Sugar Pie pumpkins for awesome pies--you can leave all of them to develop on the plants--in this case, smaller is better. My mouth is watering-time to bake a Sugar Pie(Honey Bun). Can't help myself.
Happy garden dreams,
Diane Dodge, Ramsey County(MN) Master Gardener