Other Common Names: giant reed, elephant grass, giant cane grass, Spanish reed, bamboo reed, donax reed, reed cane, reed grass, Danubian reed, Italian reed
Weed class: monitor list
Native to: Asia
Is this Weed Toxic?:
not known to be
Why Is It a Noxious Weed?
How would I identify it?
Giant reed is a large perennial grass with stems that can resemble bamboo. Plants are mostly glabrous and can grow up to a height of 20 feet or taller. It has well-developed, creeping rhizomes that are typically more than 1 cm thick and often form a dense network.
Flowers (florets) are in large, terminal, plume-like panicles. Panicles are open with ascending branches or contracted with more or less erect branches. Spikelets are comprised of 2-4 florets. Floret stalks (rachilla) are glabrous.
Leaves are alternately arranged, 2-ranked (in one plane), pale green to blue-green in color, 2 to 3.2 inches wide at the base by 11.8 inches to 3.28 feet long. The blades are flat and taper to a fine point, with the middle and base of blade about equal in width. Leaf margins are rough to the touch (scabrous) . Blade bases (region of auricles) light to dark brown, more or less broadly rounded to heart-shaped, clasping the stem, often with long, wavy hairs along the margins.
Giant reed stems, also called culms, can grow up to 30 feet tall in large tussocks or hedges. The culms grow 0.4 to 1.6 inches in diameter and have long hollow internodes of varying lengths, generally 5 to 12 inches. First year culms are unbranched and then culms commonly branch the second year and may only have leaves on the branches.
Fruit Seed Description
Giant reed fruit is a single-seeded dried fruit (a caryopsis) that is light brown and 3-4 mm long. North American populations are not known to produce viable seeds.
May Be Confused With
Giant reed is similar to, but usually larger than, common reed, Phragmites australis, another large grass in Washington. Common reed has a native and non-native strain, of which the non-native strain is a Class B noxious weed and somewhat common in parts of Washington. Generally giant reed is taller with thicker stems, thicker rhizomes and wider leaves than common reed, but there is some overlap. Giant reed has a wedge-shaped, broad, round-lobed or clasping leaf base while common reed leaf bases gradually taper or narrow. Giant reed leaves are also arranged in one plane (2 ranked), while common reed leaves are not arranged in one plane.
Where does it grow?
Giant reed grows in moist places in a variety of soils, from heavy clays to loose sands, but grows best in moist, well-drained soils. It is typically terrestrial but tolerates flooding. Plants establish in riparian areas, floodplains, ditches, culverts, and roadsides. It can often be found along drainage ditches, where it was planted for bank stabilization. Plants tolerate some salinity and extended periods of drought but not in areas with prolonged or regular periods of freezing temperatures. Arundo donax grows in full sun to part shade and can survive in low light levels.
How Does it Reproduce?
Giant reed is currently known to spread only by vegetative means in North America, since it does not produce pollen or viable seed. Plants vegetatively reproduce from rhizomes, rhizome and stem fragments, and layering.
How Do I Control It?
For More Information
See our draft written findings on giant reed Arundo donax
Whatcom County NWCB Fact Sheet on giant reed