Certified GKH Gardening Expert
I think this depends more on the type of charcoal used. If it's natural wood charcoal then it's okay to put the ashes in your compost. If it is the type that has additives (chemicals), including lighter fluid, then I wouldn't use it in compost. Check the ingredients and the label. Also, be sure to let it sit for several months to age before using on plants when putting the ashes in the compost.