Giant Reed


giantreed1Giant reed (Arundo donax)

(Poaceae) Considered very invasive and is on the Hawaii State Noxious Weed List.


This large, clump forming grass is one of the fastest growing terrestrial plants in the world, growing 4” a day and up to 8 m (16’) tall. It has stiff leaves with a clasping connection to the stem and small hairs along the margins which are felt when the leaf is rubbed in the wrong direction. Its long leaves grow to up to 70 cm (2’) long in an alternate pattern along a single plane. Large plume shaped flowers up to (1 m) 3 ft in length develop between March and September. Forms thick masses of scaly rhizomes (horizontal underground roots) and has hollow stems.


Giant reed grows in wet areas, such as in coastal areas, in wetlands, along streams, ditches, and rivers. Once established this grass forms impenetrable thickets that can cover several acres with clonal root masses up to 3’ thick. It outcompete all other vegetation, traps debris, reduce water flow, is a fire hazard when dry and eliminates wildlife habitat. Spreads easily by root and stem fragments floating downstream and taking root, or when dirt containing root pieces are moved (e.g. in topsoil or on heavy equipment such as bulldozers).



Kauaʻi: Eight known populations, mostly on the west side. KISC is working to control these populations and encourages landowners to replace these with non-invasive alternates.

Oʻahu: Several ornamental plantings. Not currently an OISC target.

Maui: Most populations are found in areas where rapid spread is unlikely, areas such as yards, open lots and dry streambeds. However, there is a strong possibility of this plant spreading to ideal habitat such as Keālia or Kanahā Ponds if people plant it nearby, or through the movement of dirt containing root parts, or by flooding of infested streambeds.

Molokaʻi: Two known populations on south side have been controlled by MoMISC. Monitoring and maintenance is ongoing.

Lanai: Presence/absence unknown

Kahoolawe: None known

Big Island: BIISC has no control efforts for giant reed and little is known about its distribution on the Big Island.

Hawai‘i-Pacific Weed Risk Assessment Score: 12. Visit for more info

Regulatory Status: State Noxious Weed (HAR 68) NOTE: it is not actually listed at , though several sites list it as a HI noxious weed

Prevention and control programs: KISC controls small populations in Kekaha, Kalāheo, Lāwaʻi, ʻŌʻmao, Līhuʻe, Hanamāʻulu, Wailuā, Kapaʻa, Anahola, and Kīlauea. Please report any sightings!

What you can do: If you see this species, call 643-PEST, visit  or call your local KISC if found on Kauaʻi.

For more information, see:



Bamboo Bambusoideae spp.
Bamboo is a perennial grass commonly seen on throughout Hawaiʻi. It can be distinguished from giant reed by clearly marked internodes along the stem.

Sugarcane Saccharum officinarum
Sugarcane is a perennial grass with similar growth structure and leaves as giant reed. It can be distinguished from giant reed by its longer leaves arranged in an opposite pattern and its clearly marked internodes along the stem.