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Harding Grass (Phalaris aquatica)

Grass Family (Poaceae)

Phalaris aquatica (harding grass).  Photo courtesy of Sepulveda Basin Wildlife, sepulvedabasinwildlife.org
Photo: Sepulveda Basin Wildlife, spulvedabasinwildlife.org


Phalaris aquatica (harding grass).  Photo courtesy of Elkhorn Slough Plants: Harding Grass, elkhornslough.org
Photo: Elkhorn Slough Plants: Harding Grass, elkhornslough.org

Description/Habitat:  Originally from North Africa, harding grass (Phalaris aquatica) is a 3-4 feet (.9-1.2 meters) tall perennial, clumping grass with short rhizomes at the base, that was introduced to United States in 1914, and was first planted by the California Agricultural Experiment Station.
Harding grass grows in dense islands and is most common in coastal valley and foothill grasslands from Oregon to the Mexican border, and is found in the Sacramento and San Joaquin valleys at elevations below 4,000 feet (1,200 m).
Leaves:  The leaves of the harding grass are bluish-green and 4-15” (10-38 cm) long and .25-.75” (.6-2 cm) wide.
Flowers:  The spike-like dense flowering heads grow 2-5” (5-13 cm) and turns green to creamy white during May and June.
Seeds:  The seed heads are at the tip of a stalk from 16 – 60 in (40 – 150 cm) in height. The seed head is a large and bulky.
The seeds of harding grass look like spikelets, and each of the spikes has 3 florets on them. This grass can produce up to 40,000 seeds per m2. These seeds will germinate whenever moisture is available, but the germination rate drops then the temperature is too high (above 85 ºF) or too low (below 50 ºF).
Flowering Period:  This grass flowers in April, and is one of the few grasses that stay green year-round.
Management:  At Fort Ord National Monument, our initial treatments were spraying harding grass with a 1.5% glyphosate solution, however since the sites are now at a more manageable size, all of the sites are treated manually. After we removed the larger plants it has become hard to identify new growth, and to account for this we generally treat this plant after the flowering has begun, but before the seeds are produced. After the flowering heads have been clipped, the plant is manually removed. The heads are bagged and removed from the area.
In general, frequent clipping of harding grass during the active growth period can be effective at preventing spread and reduce tillering. There is no set opportune time for clipping to have the greatest effect, but tillering is typically suppressed when plants are cut during flowering. It has been found that clipping the grass later in the spring retards growth more severely than clipping at the beginning of flowering. In addition, clipping at the end of the growing season when soil moisture is low reduces growth during the following year. While there has been some disagreement on the timing of clipping, repeated clipping or mowing has been found to be an effective mechanical treatment for harding grass, no matter when it was attempted. Clipping can be done during any of the different time periods listed above.
Conducting prescribed burns in the winter, every two years, has shown to be effective in reducing subsequent growth for about two years. During this time more competitive fire-adapted plants come back and increase their biomass. These burns have had the highest success rate during the winter when harding grass is starting to sprout a large number of new shoots, and eliminating a large amount of competition for the native plants.
At locations other than Fort Ord National Monument, different herbicides have been used, but for them to be effective the chemicals had to have a high application rate. An integrated approach of repeated mowing and an application of glyphosate to resprouts seem to be the most effective means of control.
Berry, Sheila, comp. "The History of Harding Grass in California." Keeping Landscapes Working 4 (Fall 2007): 5-7. Print.
"Elkhorn Slough Plants: Harding Grass." ElkhornSlough.org. Elkhorn Slough Foundation. Web. 04 June 2012. <http://www.elkhornslough.org/sloughlife/plants/harding_grass.htm>.

Harrington, Kerry. 2000. Phalaris aquatica. Pp. 262-266 in Bossard, C. C., J.M. Randall, and M. C. Hoshovsky. Invasive Plants of California's Wildlands. University of California Press. Berkeley, CA.

Peterson, David L., and TunyaLee Martin. "Phalaris Aquatica." Bugwoodwiki. The Nature Conservancy, 16 May 2012. Web. 04 June 2012. <http://wiki.bugwood.org/Phalaris_aquatica>.

"Phalaris Aquatica (hardinggrass)." Cal-IPC: Phalaris Aquatica. California Invasive Plant Council, 2012. Web. 04 June 2012. <http://www.cal-ipc.org/ip/management/plant_profiles/Phalaris_aquatica.php>.

"Plants." Santa Cruz CNPS Local Plant Communities. Watsonville Wetlands Watch. Web. 04 June 2012. <http://www.cruzcnps.org/CoastalTerracePrairie.html>.

Last updated: 08-20-2012