The weak acids in apple cider vinegar will break down the minerals in shells or bones making them water soluble, in forms that plants can use directly. These can be applied as a spray onto plant leaves or simply applied to the soil around the base of the plants. Bones and shells are often thrown away so are available for free from restaurants, fish markets or other food service locations. Close the waste gaps and make your own highly effective mineral amendments for low cost of free. You can also make you own apply cider vinegar to further reduce cost and waste. Visit us at NigelPalmer.com for information about mineral amendment analysis, upcoming workshops, podcasts and other educational opportunities. For mineral and biology amendment recipes that you can make at home for free or low cost that close the waste gaps check out my book "The Regenerative Grower's Guide to Garden Amendments" available from Chelsea Green Publishers.