Warm Season, Native Ornamental Grasses for the Home Garden

Providing dramatic bursts of textured foliage, habits of every kind and distinctively intricate flowering, warm-season ornamental grasses create a feeling of being in nature. This is just the start of their ornamental prominence. Their bountiful displays are ever changing, lasting well into fall and winter.

Native ornamental grasses provide important wildlife habitat, shelter and food from both seeds and the insects they attract. Warm-season grasses, with their bunchy, stiff-stemmed upright growth, provide structure for nest building, protection from weather and predators, and ground openings for wildlife foraging. These grasses also support a variety of insect communities, including larval caterpillars.

Features of Ornamental Grasses in the Poaceae Family

Members of the Poaceae are considered to be true grasses. In the field, Poaceae grasses have a cylindrical hollow stem called a culm. Solid swollen nodes or joints appear along the culm. Other "grass-like" ornamental plants that are not true grasses, such as sedges that belong to the genus Carex in Cyperaceae, have triangular-shaped solid culms with three edges and without joint nodes. Rushes in Juncaceae have a rounded, solid culm without joints. 

Grass plants grow in two main ways, either clumping or running.  The vast majority of warm-season grasses are clumping, also known as a bunch grass. These grasses have discrete crowns, tending to stay mostly around their planting area. Fewer warm-season grasses grow via "runners," which spread by rhizomes or stolons, usually growing beyond the area where they were planted. In either case, new seasonal growth of grasses emerge with shoots or tillers. 

Figure 2.  In summer, prairie dropseed (Sporobolus heterolepis) - distinctive dense arching mound of fine foliage and airy flowering panicles by Thomas J Mrazik, Penn State Master Gardener.

Warm-season ornamental grasses are perennial plants often referred to as C4 plants. Cool-season grasses, on the other hand, are known as C3 plants. The number refers to the quantity of carbon atoms initially produced during the process of photosynthesis which is key to how grasses are able to adapt to different environmental conditions. One consequence of their unique photosynthetic process is that warm-season grasses are more often drought tolerant due to high light and temperatures. Thus, they tend to adapt well to hot, dry weather, usually staying "green" in July and August.

Warm-season grasses emerge in late spring to early summer, with flowering extending from mid to late summer and even into early fall.  Their ornamental features mature well into fall and even winter. In contrast, cool-season grasses emerge in late March through April and mostly flower by early summer.

Figure 3.  In summer, side oats grama (Bouteloua curtipendula) - striking red-orange anthers on flowering raceme of pendulous oat-like spikes by Thomas J Mrazik, Penn State Master Gardener.

Ornamental grasses have distinctive flowers but with no petals or sepals. A floret is the basic flower unit of an ornamental grass. It is comprised of bracts or small scales named lemma and palea. A fertile floret has an enclosed reproductive stamen, which includes pollen, an anther, and a pistil. An assemblage of more than one floret is a spikelet, with its outer bracts named glumes. Bracts might be tipped with a long, hairy-like, bristly extension called an awn. Grasses do not have nectar to attract pollinators. They are wind-pollinated, developing seeds or grains later in the season. Many of these grasses are host plants for various larval caterpillars.

Florets or spikelets are held atop the main stem or culm. The culm has no branches but is sheathed with leaf blades that extend outward, forming the plant's foliage. Typically, the foliage habit of these attractive grasses is either tufted, mounded, or upright. 

Ornamental grass flowers have several patterns of inflorescence. Common types are either spike, raceme, or panicle, each varying to the extent of how the grass flower branches off the culm. For example, a panicle shows the most open and longest branching inflorescence, while a raceme is shorter, and a spike typically adheres directly to its stem.

Figure 4. Typical parts of a grass plant. Forest Practices Branch, Ministry of Forests, British Columbia.  Remedial Measures Primer V1. Chapter 6.

Benefits of Warm Season, Native Ornamental Grasses

The warm-season ornamental grasses listed in Tables 1 and 2 are often found in public gardens, natural landscapes, and home gardens. Table 1 lists grasses of tall mature height, while Table 2 lists those of medium-low mature height. The tables provide highlights of each grass’s ornamental features and growing considerations.  Note that ornamental features vary depending on the plant’s maturity and growing conditions. Cultivars of warm-season grasses also vary in features from those of the straight species.  An example includes some of the common cultivars of Panicum virgatum, such as 'Shenandoah' noted for its burgundy-red color foliage; 'Heavy Metal' for its metallic blue-green color foliage; 'Northwind' for its olive blue-green color foliage and compact, vertical form; and 'Cloud Nine' for its taller height, up to 7 feet. 

Figure 5. In summer, 'Shenandoah' switchgrass (Panicum virgatum) - bold burgundy-red foliage with airy flowering panicles; upright habit by Thomas J. Mrazik, Penn State Master Gardener.

Each warm-season ornamental grass has its own distinct ornamental beauty comprised of its foliage habit, color, culm, flowers, and type of inflorescence, and then, later in the season, how those ornamental features mature and seeds develop. Aesthetics are enhanced by planting multiples of a grass, such as three or more in a clump, band, or drift.  Such a wide variety of distinctive ornamental features offers the home gardener many design options and ways to pursue new styles, especially those that are naturalistic.

Figure 6. In fall, purple love grass (Eragrostis spectabilis) - wispy panicles of soft reddish-purple flower spikelets. Foliage matured from green to copper color by Thomas J. Mrazik, Penn State Master Gardener.

Benefits of warm-season ornamental grasses in the home garden include:

• bursts of foliage by early summer
• ornate flowering from mid-late summer, even into early fall
• maturing forms and colors, lasting well into fall and even winter
• companion intermingling with petal plants and foliage
• thoughtful sequencing with cool-season ornamental grasses
• centerpiece of naturalistic, meadow-style gardens and landscapes

According to the USDA, these warm-season grasses are native to the continental United States, including Pennsylvania. The one exception is Bouteloua gracilis. Although it is not native to Pennsylvania, it is well suited for Pennsylvania home gardens based on its USDA hardiness zones, growing considerations, and current use in public and home gardens.