2009, The Washington Post Perennials whose top growth has withered or looks ragged can be cut back now as part of the fall garden cleanup. Ornamental grasses that remain upright should be left for winter interest and cut to the ground in March. Grasses that have been battered by wind or rain, however, should be cut back now. Adrian Higgins blogs about vegetable gardening Mondays at www.washingtonpost.com/allwecaneat. Find more about gardening online: Follow the fall blooming calendar and watch how-to gardening videos at www.washingtonpost.com/home. 