So sorry I do not know why your ornamental grasses died and need more info to make a guess. Where do you garden? Perhaps a very wet winter caused them to rot. Perhaps a very cold winter caused them to freeze. In a warmer climate a fungal infection could have done them in. Perhaps a Master Gardener in your area will know what was happening to have caused the problem. Not sure what a gracillus grass is. Maybe if you sent a photo I could be of more help. Keep growing, Marianne Binetti