Cindy, a picture of your hillside site would help us here. Also we need to know what is the end result you want?
Is there irrigation, or a water supply to the area so you can water the grasses until they are well established?
Are you wanting to plant clumps of the grasses with mulch or stones or some other groundcover in between?
Or do you want the grasses to eventually cover the whole area?
Or? What kind of ornamental grass are you thinking of? How many, or how much grass are you thinking about?
Sorry for the 20 questions but . . . can't really help you without knowing these things.
