Cool Season, Native Ornamental Grasses for the Home Garden

Spring Up!  Cool-season ornamental grasses boldly announce the early gardening season, bursting forth with substantial foliage and showing interesting habits, textures, and varied leaf hues.  Later in the spring, these grasses begin to flower, offering charming inflorescences. Their eye-catching displays and movement extend into the late season, as colors and forms mature and showy seed heads appear, offering an ornamental spectacle throughout much of the year. And like all native plants, they support biodiversity and garden ecosystems, helping native wildlife thrive.

Ornamental Grass Basics

While there are other grass-like ornamental plants, such as sedges belonging to the genus Carex in the Cyperaceae, along with rushes in the Juncaceae, these are not considered true grasses. True grasses are members of the Poaceae. They have cylindrical hollow stems and solid swollen nodes on the culm, the part of the plant also known as a jointed stem. Sedges, however, have triangular-shaped solid stems with three edges and no nodes. Rushes have a rounded, solid culm without joints.

True grasses can be either cool-season or warm-season perennial plants. Cool-season grasses emerge when temperatures are between 60–75°F. After flowering in early summer, further growth stalls. Their established ornamental features mature late into the season. In contrast, warm-season grasses break dormancy at higher outdoor temperatures and don’t flower until mid to late summer, or even into early fall.

The flowers of ornamental grasses do not have petals, sepals, or nectar. A single flower is called a floret, consisting of both stamen and pistil, which are enclosed by bracts, small scales called lemma or palea.  An assemblage of more than one floret is called a spikelet. Its bracts are known as glumes and are sometimes tipped with long, hairy-like, bristly extensions referred to as awns.

Spikelets, or grass florets, are held atop the terminal end of the central culm, or main stem.  The spikelets are arranged in patterns called an inflorescence. The most common inflorescence types are either spike, raceme, or panicle, each with varying degrees of branching off of its own stem, named a rachis.  A panicle usually has the longest, widest branching, while a raceme’s inflorescence is much shorter. The grass’s culm has no branches, but is sheathed with leaf blades which extend outward, forming the plant's foliage. Most often, the foliage is tufted, mounded, or upright.

Grass plants spread by rhizomes or stolons, or they grow as a discrete clump that forms a crown, inhabiting their planting area. New growth of perennial grasses emerges with new shoots or tillers. Grasses are often wind-pollinated, their spikelets developing into seeds or grains later in the season.

Benefits of Cool-Season, Native Ornamental Grasses

The cool-season ornamental grasses included in Tables 1 and 2 are grown in both public gardens and home gardens.  Table 1 lists tall mature-height grasses, while Table 2 lists those of medium mature height. For each group, there are highlights of ornamental features and growing considerations.  Ornamental features may vary depending on plant maturity and growing conditions. Regardless of height, they all share the same basic grass parts:  floret (flower), culm (stem), and foliage. Each part adds unique ornamental features to a grass’s overall appearance. 

You will find that every cool-season grass has distinctly different and unique ornamental features, offering home gardeners many options to enhance their home garden or pursue new garden styles.

Specifically, the garden benefits of cool-season ornamental grasses include:

• early spring foliage with flowering by early summer
• naturalistic, simple, soft styling
• movement and sound
• maturing, long-lasting forms and colors, well into fall
• sequencing with later, warm-season ornamental grasses
• companion intermingling with the petals, flowers, and foliage of summer plants

According to the USDA, the cool-season grasses listed in the table are native to the lower 48 United States.  All are native to Pennsylvania, except for Diarrhena americana, Festuca idahoensis, and Nassella tenuissima. Although these three are not Pennsylvania natives, they are well-suited for Pennsylvania home gardens based on their USDA Plant Hardiness Zones, growing considerations, and current use in public and home gardens.