How to Plant & Grow Flowering Rush (Butomus umbellatus)

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how to grow flowering rush in ponds
Flowering rush is distinguished from true rushes by its cherry-like pink blossoms, but otherwise is difficult to tell apart. Photo by Stefan.lefnaer, CC BY-SA 4.0

Flowering rush is a perennial aquatic plant in the Butomaceae family. Despite its name, this plant is not a true rush. However, it does behave similarly to true rushes, being most commonly found in moist soils such as those present in wetlands, marshes, along creek beds, and pond margins.

When not flowering, this species can be difficult to identify, as it tends to look like many other grass-like aquatic plants. When flowering rush is in bloom, it produces clusters of attractive pink blooms, which look somewhat similar to cherry blossoms, and this is what most easily distinguishes it from true rushes.

Flowering rush produces beautiful flowers and can be an excellent addition to ponds within its native range of the UK and other portions of Eurasia. However, it can become problematic in ponds and gardens elsewhere and is not recommended outside of its native range. It’s incredibly invasive, and very often banned or illegal, in North America due to its invasive and destructive nature in these areas – do not purchase or grow if you live outside of its native range.

Facts, Benefits & Uses of Flowering Rush

southern hawker dragonfly
Within its native range, flowering rush is especially important to the life cycle of dragonflies, like Britain’s southern hawker.

While a single flowering rush plant is not problematic, this species can form dense stands that may crowd out native plants and other wildlife. It can even crowd out fish species, as it can take over habitat that was once more open for swimming and decreases spawning habitat. Flowering rush can spread through seeds, but also through rhizomes and bulbils—bulb-like plant sprouts that can detach and spread through water. Interestingly, many populations of flowering rush are considered to be sterile because they cannot reproduce by seeds, but instead rely entirely on spread through their rhizomes and bulbils.

Flowering rush is native to Europe and parts of Asia, but was introduced to North America in the late 1800s. It may have been intentionally brought over as an ornamental plant, but there are other hypotheses about its origins, such as soil-based ship ballasts that may have been harbouring the seeds. Since then, it has become an established invasive species in many locations. In fact, it is illegal to buy or sell flowering rush in many states in the U.S., as well as some areas in Canada.

It can be very difficult to eradicate flowering rush once it is established. For one, this species can be hard to distinguish from other, native species unless it is in bloom, and therefore a permit is absolutely required to remove it to help prevent the accidental eradication of native species. In addition, improper control measures can lead to even more spread, as new plants can become established from root fragments.

In areas where flowering rush is native, such as the UK, it is an important plant for dragonflies and damselflies. Adults lay eggs on the leaves, and nymphs use the plant to emerge from underwater to start their adult stage. Bees, flies, butterflies, and moths also visit this plant and pollinate its flowers. It can be quite useful in helping to naturally filter water and prevent sediment erosion, as well.

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Flowering Rush Fact Sheet:
Herbaceous Aquatic Perennial
USDA 3 – 10
Full sun to partial shade
July – September (Summer)
Height: up to 152 cm (60 in)  Spread: potentially extensive
5 – 15 cm (2 – 6 in); deeper for mature plants
pH 5.0 – 7.0

Flowering Rush Growth, Hardiness & Climate

flowering rush butomus umbellatus growth rate size
Flowering rush grows well either directly in water or moist pond margins, where it can reach up to 5 feet in height. Photo by Christian Fischer, CC BY-SA 3.0 Lower Saxony, Germany

Flowering rush grows quickly, and does best in shallow waters or in very moist soil, as is common among obligate wetland plants. It will grow enthusiastically at the edges of a pond or stream. When it reaches its full size, it can be up to five feet tall. This plant is a prolific spreader, and can be extremely invasive outside its native range. Many locations have made growing the plant illegal because of how substantial its spread is.

Flowering rush has a wide range of hardiness zones where it can thrive (3-10), which further contributes to its ability to establish in a variety of locations. It can grow in shallow water as well as being completely submerged.

How to Plant Flowering Rush In Ponds

how to plant flowering rush
To help control spread, flowering rush can be planted in pots. Photo by 阿橋 HQ, CC BY-SA 2.0

It is extremely easy to establish flowering rush plants. To propagate from seeds, plant in moist soil and transfer to the margins of your pond once sprouted and somewhat established. Flowering rush can also be easily grown from a rhizome cutting. This plant will grow at the margins of a water source, growing tall above the waterline, as well as completely submerged. If completely submerged, this plant is much less likely to produce flowers, and should be initially weighed down or placed in a pot at the bottom of the pond until its roots are able to hold it in place.

How to Care For Flowering Rush

how to care for flowering rush
Flowering rush grows best when planted in water or damp soil with ample access to sunlight. Photo by Andreas Rockstein / CC BY-SA 2.0

Flowering rush grows best in shallow water with plenty of access to sunlight. It tends to be an easy plant to care for, and will spread enthusiastically.

You can divide flowering rush, but you should keep in mind the fact that dividing the plant will likely lead to the propagation of more plants. In fact, a recommendation for limiting the spread of flowering rush is to limit disturbance, as it is able to spread easily from bulbils that detach and float as well as rhizomes.

How to Winter Flowering Rush

Flowering rush is winter-hardy in zones 3-10, and will not die back due to cold in these areas. When grown within these hardiness zones, flowering rush requires no special care to survive the winter. If you live in a hardiness zone outside of this plant’s range, it is recommended to consider a different species, as flowering rush is likely not native to your area and has a high potential to cause problems in your pond.

Is Flowering Rush Toxic, Poisonous or Invasive?

Flowering rush is native to Europe and Asia but is invasive elsewhere. It has become established in North America and is extremely invasive to the point of being outlawed in certain states. This plant spreads easily, through seeds, rhizomes, and bulbils. If pieces of rhizomes break off, they can even travel in water currents and establish quite far away. Flowering rush tends to form large clusters of plants and can easily crowd out native species. It is also very difficult to eradicate once established.

Flowering rush is not thought to be toxic. Any problems that flowering rush causes have to do with spreading and crowding out other plants, rather than toxicity.

Is Flowering Rush Edible? Will Fish Eat it?

Flowering rush rhizomes are rich in starch, and some people do choose to eat them. However, they are not said to be especially appealing to eat. Some animals, such as muskrats, frequently eat these rhizomes. In fact, muskrats are thought to be a factor in the spread of this plant.

Your fish will likely not try to eat flowering rush, but it is not thought to be toxic, and therefore should not harm a curious fish who decides to taste it.

Where to Buy Flowering Rush & Seeds? (UK & US)

Flowering rush is easily obtained from plant nurseries in its native ranges in Europe and Asia, both in person and online. In other areas of the world, you may have to order it online. However, many locations have outlawed this plant due to its invasive properties. Please be aware of whether you are planting non-native species in your area! Flowering rush is a beautiful addition to many ponds within its native range, but it is best to consider planting a different species if you live elsewhere.

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