Flowering rush is a perennial aquatic shoreline plant, native to Eurasia and was likely introduced as a garden plant in the late 1800s. Flowering rush can now be found from Nova Scotia to British Columbia and is very hardy, being able to survive in a large range of temperatures. It is a popular ornamental water garden plant that is widely available in garden centres and nurseries. 

Characteristics

Flowering rush is easiest to identify when it produces its characteristic umbrella-shaped clusters of upright flowers. Each individual flower has 3 petals and 3 sepals that vary in colour from white to a deep pink. The leaves are long and narrow with a triangular cross-section and the tips are generally twisted in a spiral shape. Depending on depth, the leaves will be erect when in shallow water and floating when in deeper water. It can grow submersed in water up to 3 m (9.8 ft) deep but grows 1 m (3.3 ft) tall along the shoreline and is primarily an emergent plant. It appears the plants need the energy from the sun to set seed and generally produce flowers in very shallow water or on dryer sites.

Flowering rush grows and spreads primarily from thick, creeping rhizomes and when disturbed, can break to form new plants. The rhizomes also produce many small tubers that can break off to form new plants. In addition, the plants also produce many seeds and sometimes produces tiny bulblets that can be carried by currents to form new plants. Flowering rush tends to colonize areas where new land is exposed as a result of lower water levels.

Distribution

The first observations of flowering rush was around the Montreal area in 1897 and from that time it spread down the St. Lawrence River to the mouth where salinity levels limit its further spread. Flowering rush is now widespread along the St. Lawrence River, in Lakes Ontario, Champlain, Erie, St. Clair and Michigan. It occurs in eight provinces and 14 states from the east coast to the west. Most of the distribution of these other locations for flowering rush are widely scattered which suggests that this is a result of escapes from ornamental gardens.

Impact

Flowering rush is described as aggressive and appears to be able to spread and displace native shoreline vegetation such as bulrushes, willows and cattails because of its thick root system. The ecological and environmental impacts of flowering rush on native flora and fauna are still not entirely known. Muskrats have been observed using the roots and stems of flowering rush to build their houses but this activity may also lead to further spread from root fragments.

In areas of abundance where flowering rush is submerged, its dense vegetation can interfere with boating and other recreational activities.

Prevention

Once in a watershed, small pieces of roots and rhizome pieces that break off can be carried to different areas to form new plants. Therefore, removing flowering rush by the roots is almost impossible without breakage or leaving fragments behind that form new plants. Cutting flowering rush below the water surface will not kill the plant but will limit its abundance and nuisance. Repeated cutting may also weaken the plant over time. Removing all plant pieces is necessary to limit spread and should be dried and composted completely, away from water or wet areas.

The best measure of preventing the spread of flowering rush into new watersheds is to not buy it and plant it. Many nurseries, garden centres, aquarium centres and the internet offer flowering rush for sale and when it escapes into wild areas, it generally survives and spreads due to its aggressive nature.