Water Smartweed (Water Knot Weed) Polygonum amphibium (P. amphibium
stipulaceum)
Preferred Water Depth and Inundation Tolerance
Species has a wide tolerance for inundation (Max: 20”/Min: moist soil).
Wildlife Value
Seeds are eaten by waterfowl. Serves as a major food source for purplish
copper butterfly. Also provides cover for waterfowl and fish.
Application/Zone
Used in lower shoreline zones. Wave tolerant.
Availability, Establishment, and Maintenance
Achenes, cuttings, rootstocks, and rhizomes may be used. Plants and
rootstocks have limited availability from commercial vendors. Collect achenes
when they are mature (July-Sept.).
One source recommends storing achenes in fresh, 32-34o F water for 3 to 6
months to stratify.
Other sources indicate that seed germinates best when stored dry at 40o F
followed by light at 70o F.
Broadcast in the spring on wet site.
To use cuttings, take 2-6 inch cuttings from top shoots and plant on site
in wet area by burying lower part of cutting. Spring drawdown increases plant
production.
Achene production is high in areas shallowly flooded during the growing
season.
Water Smartweed (Water Knot Weed) Polygonum amphibium (P. amphibium
stipulaceum)
Mature Height
Up to 3 feet
Plant Type
Perennial emergent herb
Indicator Status
Obligate
pH
5.4-8.8
Nutrient Load Tolerance
Moderate
Salt Tolerance
Low
Siltation Tolerance
Moderate to high
Flowering Color and Time
Red to pink
June to August
