Switchgrass, Panicum virgatum, is a robust perennial grass native to the vast prairies of North America. This warm-season plant serves various purposes, from providing forage for livestock and creating valuable wildlife habitats to its increasing role as a biofuel feedstock. Among its many attributes, the mature height of switchgrass stands out as a particularly noticeable and adaptable feature, influenced by both its genetic makeup and surrounding environmental conditions.
Upland and Lowland Varieties
The genetic background of a switchgrass plant is the primary factor determining its potential height. Two distinct genetic types, known as ecotypes, have evolved: Upland and Lowland varieties. Upland ecotypes are shorter, growing 3 to 6 feet tall. These varieties are well-suited to drier conditions and northern climates, often found on well-drained soils. ‘Cave-in-Rock’ and ‘Sunburst’ are examples of Upland cultivars adapted to cooler regions of the North Central United States.
Lowland ecotypes are taller, reaching 6 to 10 feet or more. These varieties thrive in warmer, southern climates and prefer moist, fertile soils, often tolerating periods of inundation. ‘Alamo’ and ‘Kanlow’ are prominent Lowland cultivars, known for their substantial biomass production and adaptation to wetland situations.
Environmental Growth Factors
Beyond its genetic predisposition, the growth environment significantly influences how tall a switchgrass plant ultimately becomes. Adequate sunlight is important; switchgrass achieves maximum height when exposed to full sun. Water availability also plays a role, with sufficient moisture promoting taller growth, although switchgrass exhibits good tolerance to drought and can grow with annual precipitation as low as 300 mm.
Soil quality, while switchgrass is adaptable to a wide range of soil types and pH levels (5.0-8.0), can still affect its stature. While it can persist on marginal lands, it generally reaches its maximum height on fertile, well-drained soils. The age of the switchgrass stand also influences height, as first-year plants primarily allocate energy to developing extensive root systems, resulting in shorter top growth. Mature height and optimal biomass yields are typically observed in the second or third year of establishment.
Seasonal Growth Cycle
Switchgrass follows a distinct annual growth pattern, characteristic of warm-season grasses. New growth typically begins in late spring, around April or May, once soil temperatures consistently rise above 60 to 65 degrees Fahrenheit. The most rapid vertical growth occurs during the summer months (June, July, and August), benefiting from high light intensity and temperatures.
Plants generally reach their maximum height in late summer or early fall, often coinciding with their flowering stage in August or September. As autumn progresses and frost arrives, active growth ceases, and the plant enters dormancy. Despite the cessation of growth, the dried, upright stalks of switchgrass commonly remain standing through the winter, providing structural interest and cover for wildlife.