What’s That Weed?

Introduced species:  Jubata grass (Cortaderia jubata)

Characteristics:  Jubata grass—also called purple or Andean pampas grass—is a very tall (up to 7 meters, or 23 feet) perennial tussock grass species.  Long, dark-green, drooping, sharp-edged leaves roughly 1 cm (½ inch) wide are clustered mostly at the base of the plant, with showy, nodding spikes of flowers arising on stems up to three times as tall as the foliage.  The flowers are pink or purple when they first emerge in early summer, but turn creamy-white later in the season.  Plants may flower twice in one year.  Note:  Jubata grass is easily mistaken for its less-aggressive cousin, pampas grass (Cortaderia selloana); see the California IPC website for help distinguishing the two, or contact the Bureau of Environmental Services Early Detection Rapid Response team at 503-823-2989. The City of Portland provides free assistance to citizens in identifying nuisance plants and methods to remove them; please contact them if you think you have found this species growing within City limits.

Spread:  Jubata grass reproduces mainly through prolific seed production; each plant may produce up to 100,000 seeds.  Curiously, seeds are viable without fertilization, allowing all-female populations to spread rapidly.  Seeds may be transported by wind, water, erosion, and animal movement; windy conditions may disperse seed over 20 miles.  The quick spread and enormous size of the plant allow it to out-compete native species, and pose hazards including fire danger and vermin (as rats often shelter in jubata grass clumps).  Native to South America, jubata grass was introduced to the US as an ornamental; it is very problematic along the California coast.

Control:  Seedlings and young plants can be dug up; larger plants are more labor-intensive to manage mechanically.  Grazing has been reported effective elsewhere; several herbicides appear to provide good control.  It is very important, at minimum, to remove seed heads before they mature.

Native Replacements:  For a focal ornamental, try oceanspray (Holodiscus discolor), which produces showy sprays of creamy-white flowers.  For a grass replacement, Idaho fescue (Festuca idahoensis) is a native perennial bunch grass; while more modest at less than a meter tall, it has attractive blue-green foliage and will do well in habitat occupied by jubata grass.