Pumpkins (Cucurbita spp.) grow during warm weather and need to be planted in soil that has warmed to at least 60 degrees Fahrenheit. Whether you're growing pumpkins for food or for carving, plan on supplying these heavy feeders with plenty of fertilizer before and during the growing season.
Choosing Fertilizers for Pumpkins
Pumpkins benefit from soil that has been enriched with plenty of organic matter, and this can work in conjunction with any chemical fertilizer you choose to add at planting time and during the growing season. Well-rotted compost or aged manure worked into the garden at planting time or a few days before provides nutrients and improves the soil's texture and drainage capabilities. A 5-10-10 chemical fertilizer blend provides the recommended amount of nitrogen, phosphorus, and potassium, which are the three most important nutrients that these annual plants need to get off to a good start.
How Much to Add
Use 3 pounds of 5-10-10 fertilizer for every 100 square feet of garden space before planting, and work it into the top 6 inches of soil. When the pumpkin blossoms appear at about mid-season, side dress the plants with 1/2 cup of a high-nitrogen 46-0-0 fertilizer or or 1 cup of 27-3-3 fertilizer for every 25 feet of row. Place the fertilizer along the rows, several inches from the pumpkins' main stems, and work it into the top few inches of soil.
The Organic Approach
Organic soil amendments, such as manure and compost, break down more slowly in the soil, and are less likely to result in over-fertilizing. If you're working with fresh manure or newly finished compost, it's a good idea to add it to the garden in the fall to give it plenty of time to age before you plant the pumpkin seeds. Aged compost or well-rotted manure can be added to the soil at planting time or several days before. In either case, spread 1 or 2 inches of compost on top of the soil, and work it in to a depth of at least 3 inches, as pumpkins send down long roots. Side dress midway through the season with another 1/2 inch of compost worked into the soil around the base of the plants. The New York City Compost Project suggests side dressing heavy feeders like pumpkins once a month.
Pumpkins are not fussy about the soil, but they perform best in a rich well-draining heavy medium with a pH of 6.0 to 6.5, which is mildly acidic. Pumpkins will still grow if the pH is slightly higher or lower. The soil should also retain enough water to a depth of 6 inches and drain off any excess, as pumpkins fare poorly in soggy soil or standing water.