Japanese Stiltgrass (also known as Mary's Grass or Packing Grass)
Microstegium vimineum · Warm-season, Annual, C4 metabolism
Grass Family
Poaceae, Subfamily Panicoideae, Tribe Andropogoneae
Grass Category
Invasive/Weed Grass, Wetland/Riparian Grass
Variety / Cultivar
No specific commercial cultivar; typically identified as the wild type invasive species.
Hardiness Zones
USDA Hardiness Zones 4-11; highly adaptable, though it dies completely after the first hard frost as it is a true annual.
About This Grass
A sprawling, delicate-looking annual grass that can grow to 1-3 feet in height. It has a distinctive bamboo-like appearance with pale green, offset leaves. In autumn, the foliage often turns a characteristic reddish-purple or bronze color before dying back. Seed heads are slender spikes emerging in late summer.
Blade Characteristics
Lance-shaped blades, 2-10 cm long and 5-15 mm wide, with a distinctive, slightly off-center silvery midrib of reflective hairs. The tips are pointed and the base is asymmetrical. Leaf vernation is rolled; ligule is a short, membranous rim with fine hairs; auricles are absent.
Root System
Shallow, fibrous root system. It spreads primarily via stolons that reach out and root at nodes, but it does not form a dense, deep sod like turfgrass, making it easy to pull by hand.
Growing Information
Origin Region
Native to East Asia (Japan, Korea, China, India); invasive throughout the Eastern United States, particularly in the Appalachian and Mid-Atlantic regions.
Growth Habit
Stoloniferous and decumbent. It roots at the nodes (layering) and forms dense, sprawling mats that smother native vegetation.
Sunlight & Water Needs
Highly shade-tolerant but also thrives in full sun. Prefers moist, acidic to neutral soils; often found in floodplains, streambanks, and moist woodland openings.
Mowing & Maintenance
Not desirable for maintenance; however, frequent mowing in late summer just before seed set (August/September) can prevent the massive seed bank from replenishing. Low maintenance as a plant, but high effort for eradication.
Special Characteristics
Extreme shade tolerance, prolific seed production (up to 1,000 seeds per plant), seeds remain viable in soil for 3-5 years, resistant to deer herbivory, and highly efficient at displacing native forest understory plants.
Ecological Information
Invasive status in North America. It offers very low wildlife value and actively degrades habitats by altering soil chemistry and preventing the regeneration of native trees and wildflowers. It is often a pioneer species in disturbed sites.