Espoma Gro-tone is no ordinary fish fertilizer. Unlike other products, Gro-tone is derived solely from farm-raised catfish that have been fed a strict diet of grains, minerals and vitamins. The protein from these fish provide your indoor or outdoor plants some of the best nutrients needed for healthy plant growth. Concentrate may be used in drip systems, hand held sprayers or spray bottles. Feed your plants every 3-4 weeks during growing season.