Flowering-rush identification and control
Legal status in King County, Washington
Public and private landowners are required by state law to eradicate this plant when it occurs on their property. Flowering-rush is a Class A Noxious Weed in Washington due to its limited distribution in the state and the potential for significant impact to state resources. It is on the King County list of Regulated Class A Noxious Weeds. For more information see Noxious Weed Lists and Laws.
This species is also on the Washington quarantine list (known as the prohibited plants list) and it is prohibited to transport, buy, sell, offer for sale, or to distribute plants or plant parts of this species, into or within the state of Washington. It is further prohibited to intentionally transplant wild plants and/or plant parts of this species within the state of Washington. For more information see Noxious Weed Lists and Laws.
Because of the difficulty in distinguishing this plant from native rushes and bulrushes, we recommend contacting the noxious weed program for a positive identification before removing. There are currently no records of this plant in King County, so if you do find flowering-rush in King County, please report the location right away.
Identification (see below for more photos)
- Leaves are thin, straight, sword-shaped, triangular in cross-section, and up to 40 inches long
- Flowering plants can be up to 5 feet tall
- Flowers grow on tall, cylindrical stalks in round-topped umbrella-like clusters of 20-50 flowers
- Flowers have three large pink petals (the three sepals under the petals are also pink and look like small petals)
- In deeper water, the plant grows submerged with floating leaves
- Bloom time is June to August
- Resembles bulrushes and true rushes when not in flower
- Bulbils (little bulb-like plant sprouts) may be present at the base of flower stalks and at the roots
- Rhizomes are fleshy and grow trailing along the ground
Habitat and impact
Flowering-rush produces numerous pea-sized bulbils that easily detach from the rhizome and are dispersed by the water. They quickly germinate on the soil or water surface and produce new plants. Flowering-rush also produces bulbils at the base of the flower stalks that also fall off and grow into new plants. Some varieties of flowering-rush produce seeds as well, but some do not. Flowering-rush also spreads through rhizomes and rhizome branches that break off to form new plants.
Flowering-rush has two growth forms. In shallow water or along shorelines, plants have stiff, upright leaves. In deeper water, the plants grow submerged and have flexible floating leaves that reach the surface and move with the water.
Prevention: Flowering-rush is sometimes sold for water gardens, so be careful to check the Latin names of plants you are buying to avoid introducing this species. When flowering-rush is present, take care not to disturb the soil as this will spread rhizome bulbils and fragments. Also, remove plants before they seed to prevent spread and do not allow any pulled plant material to return to the water.
Small patches: Plants can be carefully dug up, although care needs to be taken to avoid spreading bulbils present at the roots and at the base of the flower clusters.
Larger patches: Controlling this species is very challenging due to its many ways of reproducing. Permits will also be needed since this plant grows in water. Please check with your local permitting office for more information. Testing is being done to determine the most effective chemical treatment for this species. Preliminary testing reported by Minnesota Department of Natural Resources suggests that treating with imazapyr (Habitat) in mid-summer during calm wind conditions may be effective. Please refer to herbicide labels for site specific control information and refer to the PNW Weed Management Handbook for additional information on herbicide use.
Additional information on flowering-rush
- Washington State Noxious Weed Control Board (external link)
- Photos and Distribution from the University of Washington Burke Museum (external link)
- Minnesota Department of Natural Resources - Flowering Rush (external link)
- University of Wisconsin Stevens Point Herbarium - Butomus umbellatus (external link)
- Butomus umbellatus images from CalPhotos (external link)
What to do if you find this plant in King County, Washington
Please notify us if you see flowering-rush growing in King County. Our program staff can provide the property owner or appropriate public agency with site-specific advice on how best to remove it. Also, because flowering-rush is not established in King County, we have an opportunity to stop it from spreading if we act quickly. We map all known locations of regulated noxious weeds such as flowering-rush in order to help us and others locate new infestations in time to control them.
Flowering-rush (Butomus umbellatus) photos
Photos on this page courtesy of Ben Legler. Please do not use these images without permission from the photographer.
Report flowering-rush in King County, Washington
- Please notify us through our online infestation form
Locate flowering-rush in King County, Washington
- Use our interactive noxious weed map and search for flowering-rush