We just went out and bought a big Hibiscus syriacus 'Minerva' bush and planted it in a large pot of topsoil. Around it we planted seeds from "Avalanche Red" and Pink Petunias. Is there anything besides limestone that we might dress the topsoil with for optimal nutritional value. If so, where can we get it? Also, is it just the flowers of the hibiscus and the petunia that can be consumed, or the leaves of the plants as well?