To dry out a whole pumpkin, choose one that is free of blemishes with a hard, shiny shell and an intact stem that is hard and firm; wash the pumpkin using a mixture of one part chlorine bleach to 10 parts water with a small amount of dish soap added; and scrub the pumpkin with a soft brush to remove any dirt. Rinse it thoroughly with cool water, and let it dry.
Washing the pumpkin helps to remove bacteria, which cause it to rot and deteriorate.
Place the pumpkin in a cool, dry spot away from direct sunlight. If drying more than one pumpkin, leave adequate space between them for air circulation. Store the pumpkins in a location with a temperature of 50 to 55 degrees Fahrenheit and less than 50 percent humidity. Turn the pumpkins every few hours, if desired, and keep them away from warm air. Using a fan in the storage space can increase air circulation.
Spray the pumpkins with a coat of clear spray paint. Decorate the pumpkins while they are in the storage area, and return them to storage when you are no longer displaying them. The pumpkins can keep for up to three months.