There are many effective ways to preserve jack-o'-lanterns. If you can carve 2-3 days before Halloween, I recommend the following preservation tricks:
1. Prevent your pumpkin from drying out by placing petroleum jelly on the cut edges of your carving.
2. Spray your pumpkin with water, cover it with plastic wrap then store it in the refrigerator when it's not on display. This helps prevent premature decomposition.
3. Soak or spray the pumpkin with water mixed with a little bit of bleach. This will help ward off mold and kill insects for a longer preservation.
If your pumpkin is showing signs of shriveling, soak it in water for several hours. The more shriveled the pumpkin, the longer it needs to soak. When the pumpkin is removed from the water, dry the inside with a towel as much as possible to impede mold growth. Dried-out pumpkins and melons can be revived almost completely with this technique.
_________________Prairie Pumpkin Carver