Organic Comfrey Cossack Cossack Comfrey is a splendid Potash Rich Organic plant food, for indoor & outdoor plants alike. It has official Organic Status through the Organic Famers & Growers.A great plant food for the development of fruit & flowers, perfect for Roses & Tomatoes, as well as any other plant that you would like to encourage to produce an abundance of quality fruit & flowers.