Image from USDA Plants Database6


Plant Data Sheet:  American Threesquare (Schoenoplectus pungens/ Scirpus americanus)




American threesquare is common throughout the world, including the Americas and Europe.3


Climate, elevation

American threesquare may be found at low elevations.4


Local occurrence (where, how common)

American threesquare occurs in the following counties of Washington State:  San Juan, Island, King, Pacific, Okanogan, Grant, Benton, Klickitat, and Kitsap.6  Of particular note are populations found in Grays Harbor, Willapa Bay, and Padilla Bay.7


Habitat preferences

American threesquare does not tolerate high salinity, so it may be found in fresh, low salt and brackish marshes.4,7  It prefers semi-shade to no shade.3


Plant strategy type/successional stage (stress-tolerator, competitor, weedy/colonizer, seral, late successional)

American threesquare is both an obligate climax species and initial community species.1


Associated species

American threesquare is found associated with smooth cordgrass, seaside arrowgrass, and Lynby’s sedge.7


May be collected as: (seed, layered, divisions, etc.)

American threesquare may be collected as seed or divisions.6


Collection restrictions or guidelines

Divisions and rhizomes may be collected in the spring.5  Seeds may be collected when fruiting ends from August to September.3,6


Seed germination (needs dormancy breaking?)

Ripe seeds will usually germinate quickly when sown in a cold frame in a pot of ~3 centimeters of water.3


Seed life (can be stored, short shelf-life, long shelf-life)

Information on seed life was not available.


Recommended seed storage conditions

Information on seed storage was not available.


Propagation recommendations (plant seeds, vegetative parts, cuttings, etc.)

Successful propagation may occur from seeds and divisions.  Larger divisions may be planted immediately, but smaller ones should be allowed to grow more before planting.3


Soil or medium requirements (inoculum necessary?)

American threesquare requires sandy, loamy, and clay soils; acid, neutral, and alkaline soils will all work.3


Installation form (form, potential for successful outcomes, cost)

Install as seedlings or divisions. 3


Recommended planting density

It is recommended that related species that grow the same height be planted at 12-15 inch (30-38 centimeters) intervals.8


Care requirements after installed (water weekly, water once etc.)

American threesquare must be kept at water depths 2-4 inches above the soil surface for 3-4 weeks after planting.1  Be careful to discourage goose herbivory by using fencing or some other innovative technique.


Normal rate of growth or spread; lifespan

American threesquare can grow to a height of 0.6 meters.3


Sources cited

(1)    Fire Effects Information System, USDA Forest Service.  Retrieved April 12, 2006.

(2)    Hitchcock, C.L. and Cronquist, A.  Flora of the Pacific Northwest.  University of Washington Press, 2001.

(3)    Plants for a Future.  Retrieved April 12, 2006.

(4)    Pojar, J. and MacKinnon, A.  Plants of the Pacific Northwest Coast:  Washington, Oregon, British Columbia, & Alaska.  Lone Pine Publishing, Vancouver, B.C., 2004.

(5)    Thompson, Peter.  Creative Propagation, 2nd Edition.  Timber Press (Portland, Cambridge), 2005.

(6)    USDA, NRCS.  2006.  The Plants Database, 6 March 2006 (  National Plant Data Center, Baton Rouge, LA 70874-4490 USA.  Retrieved April 12, 2006.

(7)    Weinman, F, et al.  Wetland Plants of the Pacific Northwest.  U.S. Army Corp of Engineers, Seattle District, 1984.

(8)    Whitinger, Dave.  Dave’s Garden.  Retrieved April 24, 2006.


Data compiled by (student name and date)

Joy Wood 5/8/06