How Pumpkins Use Nutrients to Grow

Soil Test

• Pumpkins require a soil pH of 5.5 to 6.8 for optimal growth, as well as adequate magnesium levels. Completing a soil test -- which a local cooperative extension or university agricultural department will usually do -- allows gardeners to fertilize soil properly before they even plant the pumpkins. If the pH is low, or magnesium is required, a simple application of lime will improve the soil. Mix in composted manure prior to planting pumpkin seedlings, and wait at least a week between lime and compost applications.

Nitrogen

• Pumpkins require more nitrogen in the early stages of development to grow lush leaves and vines, as well as a strong root system. However, if it receives too much nitrogen, it can delay flowering -- and ultimately fruit production. If your plant is healthy but is not producing flowers, withhold adding additional nitrogen so that the plant can focus on developing fruit instead of continuing to grow. When adding nitrogen through a commercial fertilizer or compost, do not place it in direct contact with the plant, as it can cause wilting and burning.

Phosphorous

• This nutrient promotes deep, healthy roots, as well as the setting and development of pumpkin fruits. By late July -- or as the plants begin setting fruit -- switch to a commercial fertilizer that is higher in phosphorous, such as a 5-15-5 ratio (5 percent nitrogen, 15 percent phosphorous, 5 percent potassium). Contact or over-application will not harm the plants.

Potassium

• A fertilizer with a higher content of potassium is required after the fruit sets, as this nutrient promotes fast and large growth of pumpkins. Add it slowly, as pumpkins can grow too fast and split their outer skin -- and possibly explode -- during this stage of development.