Agents Corner

Switchgrass adds interest, versatility in garden

Amy Dabbs, Clemson Extension Urban Horticulture Extension Agent

Switchgrass (P. virgatum) has made headlines recently, as researchers with the U.S. Department of Energy found that it has excellent potential as a biofuel. This native grass is under close scrutiny for its fuel potential because it thrives in nearly every part of the country, can be grown easily from seed and does not require a lot of agricultural inputs such as fertilizer, pesticides or water.

Researchers are not alone in utilizing versatile switchgrass.  Farmers feed its lush, warm-season growth to livestock and plant it as a windbreak between fields. 

Engineers utilize switchgrass to stabilize soil and to control erosion.

Gardeners find that switchgrass makes a beautiful addition to naturalized gardens, wildflower meadows, perennial borders, pollinator gardens, rain gardens, bioswales, and many other landscape situations.'Rotstralbusch' Switchgrass

A native bunchgrass, Panicum virgatum once comprised a large part of the prairie that covered much of the Midwest and Southeastern United States. Other species within the genus fill ecological niches, including the salt tolerant coastal species P. amarum.

Switchgrass is a clump-forming perennial that typically grows from 3 to 5 feet tall and may reach a height of 6 feet when in bloom. Grow switchgrass in full sun where its striking vertical growth habit can be shown to full advantage, since it tends to flop when planted in shade.

Blue-green foliage unfolds quickly when spring weather warms the soil, but switchgrass really shines in the late summer and fall.

Large, showy panicles of fine-textured, reddish-purple or gold tinged flowers billow above foliage that turns golden yellow in the fall.  After the showy fall color fades, the plant mellows to wheat brown and the dried flowers provide visual and auditory interest when the wind rustles among the plants.

Although switchgrass may be planted any time in Lowcountry gardens, fall or spring are the best times. Water well after planting and maintain even moisture until established.

After maturity, switchgrass will tolerate both wet and dry spells equally well, making it ideal for rain gardens, bogs or bioswales.

Maintaining switchgrass is simple. Cut the grass back in the spring when new growth begins to emerge. Switchgrass is not fussy about soil pH or fertility, but avoid nitrogen fertilization when plants are young to prevent competition with cool season weeds. Over fertilization, or very rich soils may cause the grass to topple over.

Mature clumps may be divided every 3-5 years.

Several improved cultivars of P. virgatum are available in the horticultural trade. One of the oldest and most widely available is 'Heavy Metal', which grows 4-5 feet tall in full sun. Its strong linear form makes it a perfect backdrop for annuals and perennials. The metallic blue foliage is upstaged in July and August by clouds of pink tinged flowers. This selection makes a nice screen and works well in bogs and rain gardens.

'Heavy Metal' may overseed but will not come true to seed, so you may want to remove errant seedlings.

'Prairie Sky' is very similar to 'Heavy Metal' but grows slightly taller and the foliage color is a more striking blue-green.

A new dwarf form, 'Cape Breeze', is a shorter version of switchgrass, reaching only 2 to 2 1/2 feet tall. This pint-sized panicum will work well in containers, or where a shorter vertical statement is needed.

'Shenandoah' emerges with green leaves that quickly take on a burgundy hue at the tips. Hazy pink flowers appear in summer, helping this grass reach its full height of 4 feet.The foliage deepens to a rich red in the fall, making it a standout for mass plantings and container gardens.Shenandoah

Considered the tallest of the ornamental switchgrass cultivars, 'Cloud Nine' reaches heights of 5 to 7 feet tall and 3 to 5 feet wide. The pale blue-green foliage is topped with fine textured clouds of golden flowers. Allow plumes to dry in place for beautiful winter interest. Remember to prune back only in spring.

Coastal gardeners will appreciate 'Dewey Blue' or Blue Sand Switchgrass, a selection of P. amarum that thrives in dry sandy soils with low fertility. This beauty boasts striking blue-green foliage and showy inflorescences in fall.

Plant switchgrass with fall blooming perennials such as Black-Eyed Susan, purple coneflower, salvias and blanket flowers for beautiful fall color and bird-friendly winter landscapes.