Flowering Rush (Butomus umbellatus)

Flowering rush

Flowering rush is an exotic plant that has been introduced into several Minnesota counties. It is an aquatic plant that can grow as an emergent plant along shorelines and as a submersed plant in lakes and rivers.

This exotic was likely brought to North America from Europe as a garden plant. Unfortunately, it also grows well in wet places. While single flowering rush plants are not a "problem," this exotic can form dense stands which may interfere with recreational lake use. Flowering rush may also crowd out native plants and in turn harm fish and wildlife.

General Characteristics

• Easiest to identify when flowering. Flowers grow in umbrella shaped clusters and each individual flower has 3 whitish pink petals. Plants only produce flowers in very shallow water or on dry sites.
• Green stems that resemble bulrushes but are triangular in cross section.
• Along shore, erect leaves and grows to about 3 feet in height. The leaf tips may be spirally twisted. Under water, the leaves are limp.
• An extensive root system that can break into new plants if disturbed.

Spread of Flowering Rush

Flowering rush is probably spread over long distances by people who plant it in gardens. Once in a watershed it spreads locally by rhizomes and root pieces that break off and form new plants. Muskrats may use parts of the plant to build houses and probably contribute to its local spread. Boaters can transport flowering rush on their equipment. Water and ice movements can easily carry flowering rush to new areas of a water body.

Flowering rush does produce seeds but studies conducted by Bemidji State University and Queens University, Ontario, indicate that only one population in Minnesota's Forest Lake produces fertile seeds. This may explain the rather slow rate of long distance spread of flowering rush compared to the exotic plant purple loosestrife, which does spread by seed.

Abundance of Flowering Rush

In general, aquatic plant abundance varies within a lake due to local site conditions and between years due to factors like changes in weather. This variation is also true for flowering rush. Annual changes in temperature and water clarity will influence aquatic plant abundance, including flowering rush.

Flowering rush is particularly sensitive to changes in water level. This plant is a “pioneer” and can easily invade areas that are not occupied by other plants. Drops in water level may expose new sites for flowering rush. Some historical sites of flowering rush have not been relocated in recent years. The reason for this apparent decline is not known but may be related to water level changes.

Control of Flowering Rush

• Native aquatic plants protect lake quality and provide valuble fish and wildlife habitat. Removal of aqatic plants may require a DNR permit. A permit is also required to remove flowering rush because it is so difficult to distinguish from native plants.
• Flowering rush is very difficult to identify, especially if it is not in flower. It closely resembles many native emergent plants, such as the common bulrush.
• Exotics often move into disturbed areas. Removing native plants may open areas for flowering rush to invade. Protecting native plants is an important way to help keep flowering rush out of your shoreline.
• Improper control methods can worsen the flowering rush problem. See below for more information.

Cutting flowering rush below the water surface is an effective method of control. Cutting will not kill the plant, but it will decrease the abundance. Multiple cuts may be required throughout the summer as flowering rush grows back from the root. All cut plant parts must be removed from the water.

Hand digging can be used to remove isolated plants that are located downstream of larger infestations. Extreme care must be taken to remove all root fragments. Any disturbance to the root system will cause small reproductive structures on the roots to break off and spread to other areas of the waterbody. Therefore, methods such as raking or pulling which disturb the root system, but do not remove it, are not recommended control strategies.

It is very difficult to kill flowering rush with herbicides. Herbicides easily wash away from the narrow leaves of this plant. Herbicides are more effective on dry banks or in very shallow water. There is no herbicide that is selective for flowering rush and care must be taken to avoid damage to valuble wetland plants such as cattails. Any use of herbicides in public waters requires a DNR permit.

Disposal Methods for Flowering Rush

Once it is removed from the water, flowering rush can still grow and spread, mainly by sending out new shoots from the root stalk. Thoroughly dry all flowering rush plant and plant pieces that are removed from the water. Aquatic plants make excellent compost, but do not compost flowering rush next to a wetland or along a lakeshore. Large piles of flowering rush should be turned frequently and spread to allow for better drying.

Don’t Buy Flowering Rush

In Minnesota, it is illegal to buy or sell flowering rush. Unfortunately, it is still sold in other states, including Wisconsin. Protect the native plants along your shoreline. If you are interested in planting flowers near a lake or wetland, choose plants that are not invasive.