Pumpkins can be planted directly into your garden by seed or with transplants. If you’re growing your pumpkins in mounds, plant the seeds about 1 or 2 inches deep, in groups of 5. Plant pumpkins in rows with 2 seeds per hole and about 2 to 3 feet between each hole. If you want your pumpkins to mature by Halloween, it’s a good idea to plant them by May or June, but make sure to keep tabs on the soil temperature. Wait to plant your seeds until the risk of frost has past.
Whether you choose rows or mounds, make sure you give your pumpkins plenty of space. It’s preferable that they are surrounded by bare ground without other crops growing. After you’ve planted your pumpkins, frequent weeding is important to keep your pumpkins healthy as they develop.
Also note that you should avoid planting pumpkins where you’ve recently had other vine crops such melons. It’s a good idea to wait at least two years before planting pumpkins in these areas.
Growing pumpkin starter plants in your own greenhouse can be tricky. This site on plug and transplant production can help.