How to Plant & Grow Floating Pennywort (Hydrocotyle ranunculoides)


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hydrocotyle ranunculoides leaves and flowers
Hydrocotyle ranunculoides has smooth, glossy leaves and small, inconspicuous white flowers. Photo by Marcia Stefani, CC BY 2.0

Floating pennywort (Hydrocotyle ranunculoides) is a plant within the ginseng family of flowering plants, Araliaceae. It is sometimes also referred to as floating marsh pennywort. H. ranunculoides is a native aquatic plant to North and South America, as well as some parts of Africa. While it is threatened in parts of its native range, it grows abundantly as an invasive species in Europe, including the UK and Netherlands, and Western Australia.

Outside of its range, floating pennywort can spread quickly and overtake canal and pond habitats as an invasive species. Floating pennywort has a very high rate of growth and has the capacity to negatively impact native fish, wildlife, plant, and insect communities outside of its native range.

H. ranunculoides is a glabrous plant, meaning that it is smooth in texture and appearance. It is also a stoloniferous species, meaning that it is capable of branching out and producing new plants from its root nodes. The new floating pennywort plants will root freely approximately every 3-10 cm (1.2-4 in.) in the water or grow freely on the surface. Floating pennywort’s highly effective propagation strategy is one reason that it can quickly and easily become invasive and overrun an aquatic environment in a short span of time.

The leaves of floating pennywort are somewhat similar in appearance to the lobed leaves of a four-leaf clover. They are approximately 2-6 cm in diameter, and rounded in shape with 3-7 lobes. The leaf margins are typically smooth and somewhat scalloped in shape. The flowers of the floating pennywort are very small and white in coloration. Each flower bears 5 petals, and they grow on the ends of the stalks in clumped, rounded structures called umbels that contain multiple flowers. They are very tiny in size, and hardly noticeable.

Facts, Benefits & Uses of Floating Pennywort

floating pennywort Hydrocotyle ranunculoides choking a waterway
Although floating pennywort helps filter water, it grows aggressively and can completely choke out wildlife and other plants. Photo by Simon Mortimer / Floating pennywort in Foudry Brook

While many of the impacts of H. ranunculoides are negative (most notably outside of its native range), there are still a few benefits that floating pennywort can provide for the environment within its native area. This plant can play a positive role in the remediation of wastewater. However, there are other plants that can perform this role more efficiently if floating pennywort is not native to your area – the risk of spread and rapid population growth of H. ranunculoides significantly outweighs the environmental benefits it may provide for an ecosystem.

Some species of wildlife do tend to utilize floating pennywort as a food source. The weevil (Listronotus elongatus), a species of snout beetle, as well as the coypu (Myocastor coypus), a large aquatic rodent, have been known to feed on H. ranunculoides. In the UK where H. ranunculoides often grows rampant and uncontrollably, the weevil has been considered as a possible biological control agent. Traditional techniques such as manual and chemical control are often ineffective.

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Floating Pennywort Fact Sheet:
PLANT TYPE
Herbaceous Aquatic Perennial
HARDINESS ZONES
USDA 5 – 11
LIGHT REQUIREMENTS
Full sun to partial shade
BLOOM COLOR
White
BLOOM PERIOD
September (late Summer)
MAXIMUM GROWTH
Height 30 cm (12 in.)
PLANTING DEPTH
No known preference (very generalist plant)
WATER QUALITY
No known preference (very generalist plant)

Floating Pennywort Growth, Hardiness & Climate

floating pennywort growing out of control
Floating pennywort will need to be managed yearly to prevent overgrowth.

Floating pennywort grows at an aggressively fast rate, and can regenerate with ease from very small fragments. It is capable of spreading at a rate of nearly 8 inches (20 centimeters) per day! Thanks to its rapid growth rate, ability to adapt to changing environmental conditions, and resistance to herbivory, floating pennywort can spread until it is covering the entire water surface.

If you are interested in growing floating pennywort in your pond as an ornamental plant, it is important to know that it can outcompete almost any other aquatic plant species and take over its environment quite easily.

H. ranunculoides blooms between the months of March and August and can thrive in a variety of climatic conditions. It typically grows in climates characterized by warm or hot summers and mild winters with lots of moisture, but it is capable of invading areas that differ greatly in humidity and temperature. While floating pennywort prefers to grow in bodies of water containing high concentrations of nitrate and phosphate, it can readily adapt to changing nutrient conditions.


How to Plant Floating Pennywort In Ponds

how to plant floating pennywort
As long as it has water and partial to full sun, floating pennywort will be happy.

Floating pennywort is easy to establish in your backyard pond, and can be planted either by seed or by vegetative propagation. This plant species does not need very much time to adapt to a new environment, and will grow very quickly after it has been introduced!

H. ranunculoides does not have any specific soil or depth requirements and can thrive in a very wide range of environmental conditions. It will often grow freely on the water surface, or it may establish roots over time if left to its own devices and not managed for.

Many people are deterred by the fact that floating pennywort grows incredibly rapidly and can overrun an aquatic environment, but there are some people who enjoy the ornamental value enough to manage for floating pennywort in their backyard ponds. Due to its rapid growth rate and invasive properties, you should only grow floating pennywort intentionally if you live within its native range. Even so, you will likely need to trim this plant back annually.


How to Care For Floating Pennywort

If you keep fish in your pond and would also like to grow floating pennywort, it is extremely important to manage the plant’s growth and prevent it from becoming too dense. This is because floating plant species like pennywort have the tendency to reduce the oxygen levels in the water column if they become too numerous, which can lead to rapid fish mortality.

Because of its high growth rate, floating pennywort can quickly overrun your pond and push out other species of plants. If you would like to keep its growth under control, you can periodically scoop portions of the plant out of your pond. This is a very easy procedure if your floating pennywort is not yet rooted, but it gets more difficult to control when the plant is held down by roots. An aquatic rake or aquatic mower may be necessary.

Cutting your rooted floating pennywort at regular intervals between the months of May and October will help to keep it under control and prevent it from fully overtaking your pond. If the cutting is required, be sure to remove the cut sections rather than leaving them as detritus, as it can easily continue growing even after you cut it at the roots.


How to Winter Floating Pennywort

Floating pennywort will experience some die back during the colder winter months, but its roots and shoots are capable of surviving underneath the water surface. When the temperatures begin to increase again in the springtime, these roots and shoots can grow into new plants. Taking measures to overwinter your floating pennywort is unnecessary, as it is a very hardy species!

H. ranunculoides may be limited by a low tolerance for frost, but other plants can provide it with enough coverage to survive the winter. Additionally, during the colder months, floating pennywort will take on a smaller and flatter form of growth along the bank of the water in order to survive until springtime.


Is Floating Pennywort Toxic, Poisonous or Invasive?

At the risk of sounding redundant, floating pennywort is extremely invasive outside of its native range of North and South America. It is very difficult, and nearly impossible, to get rid of once it has been established in a habitat. Sales of floating pennywort are even banned in the UK because of their highly invasive properties and threats to local flora and fauna!

Floating pennywort is not known to have any toxic properties for humans, wildlife, or fish.


Is Floating Pennywort Edible? Will Fish Eat it?

Pennywort plants are edible for humans. In fact, the stems, leaves, and even the roots are all considered to be palatable! Pennywort is known to have a fresh herbal taste and has been compared with the flavors of wheatgrass, parsley, and cucumber. If you do plan on consuming this aquatic plant, it is important to collect it from a clean water source and make sure that it is thoroughly washed before consumption to avoid ingesting any potentially harmful bacteria.

Some Asian grocery stores even sell drinks made from pennywort plants – consuming significant amounts of pennywort in its raw form has been said to help lower blood pressure. It should be noted that data on the validity of this is lacking.

Fish have been known to nibble at floating pennywort if it is growing in their habitat, but H. ranunculoides has a greater negative impact on fish than a positive one. When left unmanaged for, floating pennywort will form very dense vegetation mats – the dense growth can deoxygenate the aquatic environment and kill off any organisms under the water surface, including fish.


Where to Buy Floating Pennywort & Seeds? (UK & US)

Since 2014, it has been illegal for retailers in the UK to sell floating pennywort due to its high degree of invasiveness and subsequent negative environmental impacts. While it may seem silly in theory for a plant to be outlawed, a violation can actually result in a £5,000 fine and up to six months in prison!

Many pond and garden aficionados strongly discourage the intentional planting of Hydrocotyle ranunculoides regardless of where you live due to its tendency to take over its environment and difficulty to control.

While there are not many resources that allow you to purchase floating pennywort online, you may be able to find it at your local nursery! If you live in the US, which is part of this plant’s native range, it’s easier to obtain either online or at local nurseries.

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