Flowering Rush
Butomus umbellatus

Name and Family

Flowering rush, Butomus umbellatus, is the only member of the family Butomaceae. The name flowering rush is a misnomer, as it is not a rush.


  • Flowering rush is native to Eurasia. 
  • It was first found in North America in 1897 along the St. Lawrence River in Quebec and has become widespread in the Great Lakes region. 
  • It was introduced as a water garden ornamental and may also have been brought here in ballast water. 
  • It escaped into natural areas where it has had a serious negative impact on shoreline and shallow water ecosystems and affects recreational activities. 
  • Flowering rush has unknown distribution on PEI, but it is thought to be very limited.

Identification Guide

  • Flowering rush is an aquatic perennial that resembles our native sedge species.
  • It can be difficult to distinguish from native sedges, unless it is in flower.
  • It can grow in dense stand both in and out of water.
  • This species is still sometimes sold in garden centers and is readily available for purchase online.
  • Here are some key features that may help to positively identify flowering rush:
    • Can grow to be 1-5 ft tall
    • Leaf blades are grass-like, can grow to a meter in length and are triangular in cross section
    • Flowers are showy, pink, 2-3 cm across with 3 petals, and grow in umbrella-shaped clusters at the top of a single flowering stem
    • Flowers between May and September
    • Roots are fleshy and rhizomatous
    • Spreads by seed or bulbets that form on the roots and break off
    • Roots are buoyant, so part that break off can float and establish downstream
    • Cold weather in the fall cause leaves to fall down, unlike the native cattail species that remain upright

What it does in the ecosystem

  • Flowering rush is an ornamental flowering plant sold in nurseries and online as an aquatic garden plant.
    • This has likely contributed to the rate and distribution of its spread. 
  • Due to its preferred aquatic habitat, bulbils, rhizome fragments, and seeds can be spread long distances by water currents.
    • Bulbils easily detach from the main plant and germinate quickly allowing new populations to become established. 
  • Wildlife and human activity such as boating and fishing, also contribute to its spread. 
  • Flowering rush grows in dense stands both in and out of the water.
    • Flowering rush can grow in water up to 3m or deeper. 
    • Even though the plant will not flower when submerged, it continues to spread by rhizomes and bulbils. 
  • Flowering rush reduces biodiversity by crowding out native wetland and shoreline plants.
  • It creates dense mats which restrict light, dissolved gases, and nutrients that would normally be available to other submerged plants and animals. 
  • Flowering rush is known to alter water temperature and cause shallow water systems to become filled with sediment. 
  • Its dense growth can affect irrigation and drainage system capabilities. 
  • It can restrict boating, swimming, and fishing activities by clogging shorelines and choking equipment.



  • The best way to manage any invasive species is to prevent its establishment in the first place. 
  • Flowering rush arrived by boat initially and can spread the same way. 
  • Cleaning, draining, and drying all aquatic recreational equipment before moving to a new area is a great first step in managing further spread. 
  • Before selecting a control method, consider the size of the infestation, your available resources, and the amount of effort you are willing to expend. 
  • Often, multiple control methods are used simultaneously. 
  • Consider the local ecosystem and what other organisms or ecological processes may be affected by management.
  • As flowering rush distribution is thought to be very limited on PEI, we would like to keep it as such.
    • Report any sightings to the PEIISC as soon as possible.
  • If working to control flowering rush after seed heads have formed, it is key to avoid further seed dispersal by cutting off and bagging the seed heads carefully.
    • Carefully place a plastic bag over the seed head.
    • Cinch the bag around the stem.
    • Clip the stem below the bag.
    • This will ensure that the entire seed head has been deposited into the bag, with little chance for accidental dispersal. 
  • If you are heavily invested in management, specialized attachments for excavators exist to remove plants on a larger scale. 


  • Hand-digging of flowering rush plants can be a feasible option for small to medium-sized outbreaks.
    • This process must be done with care, as flowering rush can grow back from root fragments that are left behind or that break off during management. 
    • Using a sharp shovel, excavate and remove the entire plant from the water to prevent root fragments from being washed away.
      • Washed-away fragments can sprout and start infestations in new areas. 
  • Cutting the plant regularly below the water level can prevent flowering, and can gradually reduce flowering rush populations over time.
    • Used alone, this method is unlikely to achieve eradication.


  • Cutting can be combined with benthic matting where feasible to further suppress flowering rush populations. 
  • Matting will also affect the surrounding ecosystem and prevent all new plant growth. Native plants will be affected just like the flowering rush.
    • Plants are not the only species affected. Benthic invertebrates, soil-dwelling organisms, and fish will also be impacted. Keep this in mind when implementing matting techniques. 
    • Along with these native aquatic species, the wildlife that relies on them will also be affected by their loss through reduced availability of food and shelter. 
  • Timing of management is crucial.
    • It is important to consider the spawning time of any fish species found in the affected wetland or watercourse, as fish reproduction can be negatively affected by management. 
    • Waterfowl that nest along the banks of many wetlands and watercourses, so check the area for active nests and delay management until after these nests have been vacated. 
    • Despite the potential negative effects of management, the negative effects of leaving flowering rush unchecked may be greater.
  • Instead of using one big tarp, it is often best to cut it to the size needed and make smaller patches. 
  • Tarping works because the root system will be deprived of light and the plant’s roots will be continuously baked by the sun. 
  • This is a simple practice on dry land, however, when this plant is being managed in aquatic environments the challenge increases. 
  • Tarps can still be placed in aquatic areas whether they are submerged year-round or even seasonally, however, the tarps will need to be modified to stay in place. Tarps placed at the bottom of a waterbody are known as “benthic barriers”, they are built to be weighted down and built to prevent billowing when gases are released by the decaying plants. 
  • Tarps are available commercially but it is also possible to build your own.
    • See our guide here for instructions on how to build a benthic mat.


  • It is unlawful to use herbicides when nearby wetlands and watercourses on PEI, so chemical controls are not a viable option for the management of flowering rush. 
  • In any case, when using chemical controls, all local legislation and manufacturer’s instructions must be followed.


  • To prevent spread during the management process, all plant material should be collected, bagged, and prepared for proper disposal.
    • Bag the plant material in clear plastic bags.
    • Mark the bags boldly with a permanent marker. Write “INVASIVE PLANT” or “FLOWERING RUSH” on the bags. 
    • If you have a place away from foot and wildlife traffic, you can dry out the material, making it much easier to move.
      • Leave the bags open and in the sun for a week to dry. 
      • Only do this if you can guarantee that the plant will not be spread from where it is drying
    • Double bag if the bags are thin to prevent accidental dispersal.
    • Tie the bags tightly and place them in your usual residential waste collection (THE BLACK BIN)
      • Never place invasive plants into the compost. This may allow them to become established once they reach the heap. 
  • All equipment used should be cleaned and all plant parts should be removed from your person, tools, and vehicles.
  • Any proper management plan will include follow-up visits.
    • These are conducted to assess the effectiveness of control measures and to manage any regrowth that may occur onsite. 
    • If regrowth is seen, you will likely need to repeat your control measures.
  • Replant the area with appropriate native plants to compete with any new growth and begin to regenerate the area to its natural beauty.
    • Reach out to the PEIISC for advice on selecting the proper plant for the location. 


Flowering rush (Butomus umbellatus ) | Fraser Valley Invasive Species Society (fviss.ca)

Flowering Rush Management in the Columbia Basin — Oregon Invasive Species Council

Flowering Rush – Alberta Invasive Species Council (abinvasives.ca)

Flowering Rush – SSISC

Flowering Rush – Ontario Invasive Plant Council (ontarioinvasiveplants.ca)