Pampas Grass
Cortaderia selloana
Washington State Classification
Class C — Widespread, County-Selected Control
Pampas grass is a nonnative species used in ornamental plantings in Washington and is a known invasive species in California and is escaped in Oregon.
Quick Reference
Identification
Growth Habit
It is a large perennial grass that grows in clumps called tussocks. Basal clumps of long, narrow leaves have sharp edges and grow to around 4 feet tall, and upright stems grow out of the tussock, up to 6 to 13 feet. Plumes of flowers bloom at stem tips, ranging in color from white, silver, cream, pink to violet. After seeds develop and spread, stems with old flowers remain through the winter.
Leaves
Leaves form a rounded tussock. Leaf blades are up to 6.6 feet long and have a prominent midrib. Leaf margins have sharp teeth, which readily cut skin. Leaves are bluish-green, their upper surfaces glabrous at base and their lower surfaces glabrous or hair toward the collar. Leaf sheaths are variable in their hairiness and the ligules consists of a dense ring of hairs.
Flowers
Plants either have all female flowers or all hermaphroditic flowers. The hermaphroditic flowers function primarily as a pollen source, and so are often referred to as male flowers. Female plants need to be pollinated by hermaphroditic plants to produce seed. The inflorescence, called a plume, is a panicle and ranges in length from 1 to 3 feet.
Fruit & Seeds
The fruit is a dry, one-seeded fruit, 1 to 3mm in size. The estimated mean number of seeds produced per plant, counted from escaped pampas grass plants, was 416,399, ranging from 54,567 to 840,905 per plant.
Impact
Pampas grass is a nonnative species used in ornamental plantings in Washington and is a known invasive species in California and is escaped in Oregon. In 2014, escaped populations of pampas grass were discovered in Washington State, with one infestation having almost 500 plants. Due to its apparent recent spread, its ability to crowd out desirable plant species and the range of conditions it can establish and survive, pampas grass is listed as a Class C noxious weed.
Ecology & Spread
Habitat
Pampas grass can invade a wide variety of habitats, including pastures, roadsides, shrublands road-cuts, logged forests, coastal shrub and grasslands (including serpentine soils), coastal sand dunes, bluffs, marshes and wetlands, inland riparian areas, and shrublands. It can grow in away from the coast where sufficient moisture is available. Please click here to see a county level distribution map of Pampas grass in Washington.
Spread Mechanisms
Reproduction
Plants spread by seed. Seeds are very light and can be dispersed in the wind and by human activity. Vegetative spread can occur when fragmented roots receive adequate moisture and develop adventitious roots.
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Control Methods
Biological Control
- There are no approved biological control agents for pampas grass.