Don't use bleach or apple cider vinegar to slow decomposition. The first is dangerous, and vinegar attracts bugs. Instead, add 1 tsp peppermint essential oils or peppermint extract to 1 pint of water, and spritz the inside of Jack (after seeds removed, and remove as much "goop" as possible to slow decomposition...the drier the better). The peppermint is a natural antifungal that will significantly slow the rot of dear Jack. Happy Halloween!!
