I wouldn't. When I planted up a steep bank a long time ago I just made holes in the grass to take the shrubs that I wanted to plant, then kept them clear and made them larger as the bushes grew. The grass roots held the soil together so that it didn't wash away. I found it best to make a flat "watering platform" behind each plant that I wanted so that the water didn't just run off and I mixed in some slow release granular fertilizer and water retaining gel into each planting hole. Keeping the moisture in on a steep bank is important and difficult to do.