PUMPKIN PUMPKIN PLANT IN 9 CM POT €1.99 Out of stock. Plant pumpkins near the edge of your garden. Space pumpkin plants 2 to 5 feet apart (depending on the variety). Grow each pumpkin on a 3-foot wide mound of warm, fertile soil that has a pH of 6.0 to 6.8. Improve your native soil by mixing in several inches of aged compost or other rich organic matter. Give your pumpkins plenty of nourishment with a continuous-release plant food. As pumpkins start to form, elevate them off the soil to prevent rotting. Harvest pumpkins once they reach their ideal color. The skin should be firm and stems will have started to wither.