According to the Purdue University Cooperative Extension, ornamental grasses rival other garden flowers in grace and beauty because of their attractive color, foliage and form. Colorado State University asserts that these grasses enhance the appearance of the landscape with their vertical growth, require low maintenance, grow in poor soils and liven up the spot in the winter when deciduous plants become barren. The three main techniques to control ornamental grasses include cutting back growth, applying root barriers and dividing growth.
Some varieties of ornamental grasses are more invasive than others. These spread rapidly and quickly, crossing over any boundaries placed specifically to keep them in place, and can choke out turf grass or nearby vegetation. According to the United States National Arboretum, a few varieties are so invasive that their supply is held back, which is why despite the hundreds of different types available, garden centers and nurseries repeatedly use only a few.
Cutting Back Growth
Grasses are vigorously pruned or cut back each spring, before the appearance of new growth, to control height and/or spread, putting a prolific grower in scale with the surrounding planting. Spread tarp over the ground so the process of cleaning up is easier. Use a sharp, clean pair of pruning shears to cut the selected grass down to 2 to 4 inches above the ground. According to gardening author Tracy DiSabato-Aust, a fellow gardener cuts back his variegated miscanthus, an ornamental grass, to 3 to 4 inches when it grows 5 feet tall, resulting in a controlled growth of between 2½ to 3 feet rather than an uncontrolled 6 feet.
Applying Root Barriers
Root barriers are a means of controlling plants or trees so invasive that they uplift and damage nearby or adjacent hardscape or pavements with their roots. According to Taylor's Master Guide to Gardening, not all but a select few varieties of ornamental grasses causes damage of this scale.
To divide ornamental grasses, remove 4 to 6 inches of growth from the crown. Insert two spades, each into an opposite side of the mound and tug to pry it apart. Cut the grass mound in smaller sections, each with roots, and replant.
Wear a full-sleeved shirt, long pants, close-tip boots, protective eyeglasses and gloves before the procedure because some grasses have sharp corners or edges that causes cuts and scratches. According to the University of California, roots of plants encircled by root barriers can escape from the base, requiring frequent checking or using another means of control simultaneously. DiSabato-Aust suggests waiting 6 to 7 years after planting the grass before you begin to divide it. This complex procedure sometimes requires the use of a saw and axe.
Care for the ornamental grass appropriately after applying the selected control technique. Water the grass weekly, mulch the area to control weeds and fertilize annually with ¾ to 1 lb. of 10-10-10 fertilizer for a 100-square-yard plot.