How to stop pumpkin from molding - Mix one tablespoon of bleach, such as Clorox, per quart of water. Pour the bleach solution into an empty spray bottle. Sponsored Links Spray the bleach solution inside the carved pumpkin as well as on the carved parts of the pumpkin. This will eliminate much of the bacteria and mold that causes those parts to rot. Allow the solution to penetrate the surfaces of the pumpkin and let it dry for 20 minutes.