Ornamental grasses bring texture, movement, and a long season of interest to any landscape design. These plants are generally categorized as either annual, completing their life cycle in a single season, or perennial, returning for many years. Perennial grasses are further divided into two growth habits: clump-forming, which grow in contained tufts that slowly widen, and spreading or running, which expand more aggressively using underground rhizomes or above-ground stolons. Their visual appeal lasts well into the colder months, adding architectural structure and subtle color to the dormant garden.
Selecting Location and Planting
Most varieties perform best when situated in a location that receives a minimum of six hours of direct sunlight each day; insufficient light can cause the plants to become weak and flop over. While grasses are tolerant of many soil types, excellent drainage is necessary to prevent root rot. If the soil is heavy clay, amending the area with organic material like compost before planting will improve its structure and permeability.
The best time to plant container-grown grasses is typically in the spring or early fall, allowing the roots time to establish before summer heat or winter cold. Dig a planting hole that is at least twice as wide as the root ball but no deeper. Placing the plant at the same soil level it was in the nursery pot is important, as planting too deeply can lead to crown rot. After positioning the plant, backfill the hole, tamping lightly to remove air pockets, and water thoroughly. Spacing should be based on the variety’s mature width to ensure air circulation and growth.
Ongoing Watering and Feeding
Newly planted grasses require consistent moisture to encourage a deep, robust root system during their first growing season. Water these young plants regularly, especially during dry spells, until they become well-established in the landscape. Once mature, most ornamental grasses are highly drought-tolerant and need significantly less water than traditional lawns or annual flowers.
Established grasses do not require regular fertilization, as they thrive in lean soil. Over-fertilizing leads to excessive, rapid growth, resulting in weak stems that cannot support the foliage, causing the plant to flop. If soil is exceptionally poor, a single, light application of a balanced, slow-release organic fertilizer in the early spring is sufficient. Applying a two- to three-inch layer of mulch around the base helps to conserve soil moisture and suppress weeds.
Managing Dormant Foliage
Dormant foliage is often left standing through the winter for its texture and visual appeal against snow or frost. The correct time to cut back most deciduous grasses is in late winter or early spring, just before the first signs of new green growth emerge from the crown. Cutting back after new growth has started can inadvertently harm the fresh shoots and make the process more difficult.
For large, clump-forming varieties, first tie the entire plant into a tight bundle using twine or a bungee cord; this simplifies cleanup. Different grass types require different levels of trimming:
- Warm-season grasses, which turn brown after the first hard frost, should be cut back severely, typically to a height of four to six inches above the ground.
- Cool-season grasses, which may retain some green color, require a less severe trim, where only about one-third of the old foliage is removed.
- Evergreen or grass-like plants, such as sedges, do not require a hard cutback but benefit from light grooming to remove any dead or damaged blades.
Long-Term Health Through Division
Perennial ornamental grasses benefit from periodic division to maintain vigor and prevent the center of the clump from dying out. This loss of vitality occurs every three to five years as the plant matures and the central root mass becomes woody and unproductive. Division is also a practical way to manage the size of a grass that has outgrown its designated space.
The timing for division depends on the grass type: warm-season grasses should be divided in late spring or early summer when new growth is visible, while cool-season grasses are best divided in early spring or early fall. To divide, first cut back the foliage to a short height to make the root crown accessible. The entire clump must be carefully dug up, and a sharp spade, knife, or even an axe may be needed to cut the dense, fibrous root mass into smaller, viable sections. Each new section must contain healthy roots and at least one viable growth point, ensuring a successful replanting.