Once you've hollowed out your jack-o-lantern or made pumpkin pies in the fall, you'll have a bunch of leftover pumpkin seeds. If you're thinking of trying to grow your own pumpkins next year, save them for planting in the spring. You can also obtain pumpkin seeds from any commercial seed supplier. Choose a variety that suits your local climate and your available growing conditions; check the seed packet for specifics.
To grow pumpkins, start them indoors from seed in mid-April or plant them outside in mid-May. They will start to sprout within two weeks. You can transplant the seedlings outside after the last frost. The plants will be finished pollinating by early July, and will begin to bear fruit---the pumpkin---by mid-July. The pumpkins will grow most through July and August. Growth slows in late August and September, and they are ready for harvest by the end of September or early October.
The bigger your pumpkins, the earlier you should start them. Start giant pumpkin varieties indoors to get a jump on the growing season so they reach their full potential. Plant them indoors in late April and early May, then move them to the garden in late May or early June. Start regular-size pumpkins indoors in early May, transplanting them outdoors in early June, or sow them directly into the garden from late May to early June. Sow miniature pumpkin seeds outdoors in the garden from the end of May through July.
Planting dates depend on your area. Pumpkins are not cold-hardy, and frost will kill the seedlings. Sowing in mid-May may be too early in the most northern climates. Wait until the last frost date is past before setting pumpkins outside. Pumpkins grow well in most cold hardiness zones, but do best in zones 4 to 9.
The best method of planting pumpkin seeds depends on the type of pumpkin you are growing. Sow vine pumpkins in groups of five or six seeds, about an inch deep in hills at least 6 feet apart. Sow bush pumpkins an inch deep in groups of three or four seeds about 2 feet apart, in rows about 3 feet apart. If transplanting seedlings, be sure the ground is warm enough; wait until at least mid-May, and in northern climates, until June.
A few weeks into the growing process, thin out the seedlings from the groups you have planted, leaving just the two strongest in each hill or grouping. Fertilize and water throughout the growing season. Depending on the type of pumpkins you have planted, you should be able to harvest within three to four months from when you planted the seeds.