It never occurred to me to grow pumpkins in pots until I visited Kim Brix who had a beautiful crop of them growing in containers in her side yard. The plants were gorgeous and healthy and the pumpkins irresistible. I knew I had to try it myself.
I decided to grow small pumpkins and bought seedlings at a local nursery. Pumpkins are easy to start from seed, but I didn't decide until late in the season so went with seedlings. If you do want to grow pumpkins from seeds, plant them about an inch deep after the soil has warmed up to at least 60 °F.
Use a Big Pot - I like large sized Smart Pots which even come in a lovely orange color. I wouldn't try growing pumpkins in any pot that wasn't at least ten gallons. Fifteen to twenty gallons or bigger would be even better if you want to grow more than one plant.
Fill Your Pot With Good Soil - Make sure you use a high quality, fast draining potting soil. The more soil the better because it will retain water, and pumpkins need a lot of water.
Make Sure Your Pot has Good Drainage - The more drainage the better. Your pumpkins will not be happy sitting in wet soil, so either use a fabric pot, like Smart Pots, or make sure your pot has lots of holes (or one big hole that won't clog) so the water can drain out.
Place Pumpkins in Full Sun - Even small pumpkins need lots of sun to develop. Make sure you pot is getting at least six hours of direct sun a day.
Feed Your Pumpkins - I always mix a slow release fertilizer in with my potting soil and then use a diluted liquid fertilizer every couple of weeks during the growing season. You can also scratch a dry slow release fertilizer into the top of your soil, during the growing season, if you don't want to be bothered with the liquid fertilizer. However, you want to be careful not to give pumpkins too much nitrogen.
Give Pumpkins Room to Grow - Pumpkin vines are grow very quickly and some can grow to amazing lengths. Some people train them up trellises or pinch them back. If you grow on a trellis, you will have to figure out a way to cradle the pumpkins. Some people use stockings or cloth attached to the trellis.
Pumpkins Need Pollinators - This sounds obvious, but many places there simply aren't enough bees and pollinators. You can hand pollinate or plant flowers that will attract pollinators near your pumpkins.
Pumpkins Need Time - Pumpkins need seventy-five to one hundred days from planting to harvest, depending on the variety.
Pumpkins Need Turning - Carefully turn your pumpkins, which usually means flipping them from one side to the other without breaking the stem. You do this for sun exposure as well as so the pumpkin doesn't flatten on one side. Some people put their pumpkins on a board or on mesh to keep them from rotting. If your ground is wet for a prolonged period, this is probably a good idea.
When to Harvest Pumpkins - This would seem easier than in reality it is. The advice is to wait until the pumpkin skin is hard enough to withstand pressure from a finger nail and until it is a bright orange. Also, when you thump it with your knuckles it should sound a little hollow. I don't know...I just guess. However, it's a good idea to use a strong pair of pruning shears to cut your pumpkin off the vine--the stem can be very tough to cut. You want to keep the stem as long as possible, so cut as far from the pumpkin and close to the vine as you can.
Curing Pumpkins - After you have cut the pumpkin off the vine, many people suggest to cure it by leaving it in the sun for a week before bringing it inside.