Sow pumpkins in the garden in spring when all danger of frost has passed, and the soil temperature has reached 65°F, and night air temperatures are above 55°F.
Pick pumpkins when deeply colored–deep orange or golden white–and stems and vines have dried and turned brown. The rind should be hard, not easily penetrated by a fingernail. Thump maturing pumpkins; a ripe pumpkin will sound hollow when thumped.
For more information on growing pumpkins, check out this great guide from Harvest To Table: