that is a really vauge question, there are tons of different kinds, organic for one, can be hard to dose but will yeild the most flavorfull bud, hardcore chems, for intense bud growth, but destroy the palatability. average ferts are a compromise between the two and time realease ferts for those who wish not to invest time or leave a trail. usually they can be found at bachmans, walmart if your in a pinch, or a gardening shop or indoor growing store.