Beware of Invasive Aquatic Plant Species...

Invasive Aquatic Plants

Invasive Aquatic Plants

When introducing aquatic plants to your garden pond it is important to use native where possible to help fight the threat of invasive species which can drain the ‘goodness’ and energy out of the water.

Non-native species in the UK can cause a variety of problems for a lot of ornamental ponds, some of the more commonly known species being Floating Pennywort ‘Hydrocotyle ranunculoides’ and Japanese Knotweed ‘Fallopia japonica’ are widely considered to be the UK’s most dangerous non-native plant.

Although people are aware of the dangers associated with non-native plants, many do not understand the scale and impact that these plants have on the delicate ecosystem of a pond.

By definition, invasive species are described as any introduced species that can out compete a native species for space and nutrients.  Introduction is usually intentional as many species can be visually impressive and used for adding an architectural effect to designs.  Unfortunately more than often, little or no thought is given to the long-term implications of the introduction.

Attractive non-native species may seem to add colour and exoticism to a pond but this will soon spread and out compete our native species, leading to a pond that quickly turns to a monoculture only able to sustain the non-native.

Popular pond plants like Parrots Feather ‘Myriophyllum aquaticum’, Water Lettuce ‘Pistia stratiotes’ & Floating Pennywort, ‘Hydrocotyle ranunculuoides’ now cause major problems to our natural lakes, streams, canals and other water ways.

Floating pennywort, often considered to be one of the most damaging species, was first found in the wild in 1990 in still or slow-flowing water bodies.  It can grow up to 20cm a day, rapidly clogging up the surface, blocking out light and reducing oxygen for other aquatic inhabitants. It has been known to block drainage ditches and storm channels, increasing the potential risk of flooding. The plant is able to regenerate from the smallest of fragments, making it almost impossible to completely eradicate from an infected area.  It is suspected that the initial plant came from a garden pond owner unaware of the potential damage a non-native species could cause. The outbreak has lead to a firm stance being taken from authorities and any action resulting in the spread of Floating Pennywort can result in prosecution.

There are a number of simple steps pond owners can take to help protect our natural aquatic environments from further damage from invasive non-native species.

Firstly and most importantly know what you are buying – a reputable aquatic retailer will have a good knowledge and understanding of aquatic plants.  Don’t be afraid to ask questions and always ask if the aquatics plants available for sale are permitted under UK legislation.

Although you can no longer buy American Floating Pennywort some suppliers and stockists are now selling the New Zealand variety; ‘Hydrocotyle nova zealandiae’, which has caused problems in other parts of the world.

Plants like Parrot Feature, an attractive oxygenator, is still available from stockists and although it is not illegal to sell or buy this plant it is an offence to plant or otherwise cause this plant to grow in the wild.

Aquatic plants will need to be managed regularly as they can become overgrown and if left to spread can lead to many detrimental conditions within the pond.  Ensure that all plant matter is composted or burnt and that any water from your pond is poured over the garden rather than down the drain or into water ways.

Avoid getting plants from other ponds as many non-invasive species carry small plant fragments from invasive species that can spread quickly, for example Azolla, Azolla spp or New Zealand Pigmy weed ‘Crassula helmsii’ can rapidly regenerate and take over your pond.

When looking for oxygenators, try and use native plants like the oxygenator Hornwart ‘Ceratophyllum demersum’ or the floating plant Frogbit ‘Hydrocharis morsus-ranae’. These plants are not only perfectly suited to the conditions found within our ponds but can be an attractive and beneficial addition.

If in any doubt contact a reputable retailer or visit the government-run ‘Be plant wise’ campaigns website at;

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