Mid to late winter is an excellent time to cut your ornamental grasses back. I try to cut them as low as possible. Make sure you have a good sharp tool to do this work. Otherwise you will be frustrated and very sore from your struggle. All perennial ornamental grasses will benefit from a good haircut… even Liriope ( Monkey Grass). So get your pruning shears out and start cutting! Don’t forget to add your clippings to your winter compost pile.