Make sure that the seeds you purchase have been treated with a fungicide to prevent rotting. Treated seeds will be coated with a neon pink color. Gloves should be worn when handling treated seeds to prevent exposure. Plant three seeds to a hill, removing all except the strongest plant when they are 4 inches tall. Give the remaining vine plenty of room - typically 8 feet in all directions.
Pumpkins have both male and female flowers on the same plant.
If you desire size over quantity, then only allow 2 pumpkins to develop per plant. Since most varieties mature in 3 to 4 months, seeding should occur by July 4th for Halloween sales. If you seed a crop during this time, be prepared to spray plants with fungicides and insecticides. I am going to have to create a Julie binder to hold all this great stuff I print out. This drought has killed my pumpkin patch and it was doing beautifully.