Yes, Osmocote is safe to use on all three of these plants. The nutrients are released slowly over time so you don't have to worry about leaf tip burn on sensitive plants like gardenias. Azaleas may benefit even more from the Osmocote made for acid-loving plants, but the regular Osmocote will provide nutrients and benefits to azaleas. Keep Growing, Marianne Binetti P.S. Merry Christmas! Hope you get some Osmocote as a stocking stuffer. The shape of the canister package fits nicely into Christmas stockings.