Vinegar.  While both bleach and vinegar are effective at killing mold, vinegar is considered a more natural, safer, and better alternative. Actually, if you use bleach, it will only do its job at a surface level and won’t be able to kill the mold for good. By comparison, vinegar has been shown to penetrate deeper into the wood and kill mold spores and colonies that may be hidden within. While on the other hand, bleach will allow it to continue to grow inside, which will result in it growing back up to the surface in the future. Additionally, chlorine bleach is too strong and is more likely to damage and stain the wood’s surface.