I am going to begin planting a flower garden tomorrow and it will consist of carpet of snow around the borders (then rocks as a barrier to keep the flowers from spilling into the yard) behind the carpet of snow will be poppies, zinnia and cosmos, maybe another couple of types of flowers. But what kind of foliage or green "filler" can I use to cover spots where flowers haven't grown, that isn't too high? I don't want it to hurt the flowers or be taller than them