Japanese Stiltgrass
Microstegium vimineum · Warm-season, Annual, C4
Grass Family
Poaceae, subfamily Panicoideae
Grass Category
Invasive/Weed Grass
Variety / Cultivar
Wild type (no distinct commercial cultivars as it is considered an invasive weed)
Hardiness Zones
Thrives in USDA Hardiness Zones 5 through 9, exhibiting strong cold tolerance via prolific annual seed production rather than perennating structures.
About This Grass
An annual grass with a sprawling, delicate habit. Grows up to 2-3 feet tall when supported by other vegetation, but typically forms a dense, low-growing, sprawling mat 1 to 2 feet high when unsupported. Bright lime-green to yellowish-green foliage with a delicate texture. Distinctive silvery-reflective stripe of hairs down the middle of the upper leaf surface. Produces slender, spike-like racemes in late summer.
Blade Characteristics
Blades are flat, relatively short (1 to 3 inches long), and lanceolate (broader in the middle and tapering to a point), width is medium to coarse (4-12 mm). Color is light yellowish-green. Vernation is rolled in the bud. The ligule is a short, membranous fringe, and auricles are absent. The most distinguishing feature is the off-center, silvery line of pressed hairs along the midrib of the upper leaf surface.
Root System
Shallow, fibrous, and weak root system. Plants pull out of the ground very easily. Does not form a permanent, tough perennial sod because it is an annual, though dense root and stem masses can contribute minor thatch and erosion control temporarily.
Growing Information
Origin Region
Native to Asia (China, Japan, Korea, India, and parts of Southeast Asia); widely naturalized and invasive in the eastern United States and parts of Canada
Growth Habit
Stoloniferous and branching; roots at the nodes when touching the ground, forming dense, expansive, tangled mats
Sunlight & Water Needs
Highly shade tolerant, frequently found in understories of deciduous forests, along shaded trails, and damp shady lawns, though it also tolerates full sun if moisture is sufficient. High moisture requirement; thrives in moist, damp soils and cannot tolerate severe drought.
Mowing & Maintenance
Low to medium maintenance as a weed. In lawns, it can be managed by frequent, low mowing which prevents seed production, but it easily rebounds from seed banks. Fertilization encourages its growth over more desirable turfgrasses. Considered a high-maintenance nuisance for land managers.
Special Characteristics
Extremely invasive, capable of rapidly crowding out native understory vegetation and standard turfgrasses in shaded, moist areas. Low wear tolerance, poor drought tolerance, high tolerance for deep shade, acidic soils, and heavy deer browsing pressure (deer often avoid it, aiding its spread).
Ecological Information
Introduced accidentally to the US around 1919 (used as packing material for porcelain). Highly invasive status; alters soil chemistry, inhibits tree seedling regeneration, and creates a high fire hazard in autumn when it dies back and forms a thick, dry thatch layer. Provides very little wildlife value compared to native plants.