To keep a carved pumpkin fresh, combine a preservative mixture of bleach and water together, and completely submerge the pumpkin in it. After that, let your pumpkin air dry and spray it with a commercial pumpkin preservative of sodium tetraborate decahydrate and sodium benzoate so bacteria and mold do not grow on it.
By soaking your pumpkin in a bleach solution, you keep it hydrated with the water while keeping it clean with the anti-bacterial properties of the bleach. After soaking and bleaching the pumpkin, smear petroleum jelly all over it to keep it moist and prevent it from drying out. For longer-lasting results, keep your pumpkin out of the sun so it does not dry out and out of the rain so mold does not grow on it. Keeping it in the refrigerator preserves your pumpkin even longer.