Start seeds indoors 3 weeks before last spring frost. Sow 4-6 seeds in slightly mounded hills 3′ across and 6′ apart. Thin or transplant seedlings to 2-3 plants per hill before vines begin to spread. Water and fertilize regularly when pumpkins form. For biggest size, keep only 1 pumpkin per vine. Harvest when vines die back and pumpkin rinds are hard.