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Plant Positive

‘Invasive plant species are now one of the biggest threats to habitats and biodiversity across the world.’ (DEFRA)

Thanks to a grant from DEFRA (the government department for environment, food and rural affairs) Natural Enterprise has launched a new project to tackle the non-native invasive plants that are threatening parts of the Island’s ecosystem.

Plant Positive: Action on Non-Native Invasive Flora
A new partnership combining Newport Rivers, the Environment Agency, Hampshire and Isle of Wight Wildlife Trust, The National Trust, RSPB and other Island organisations has been created to target species such as Japanese knotweed, Himalayan balsam and creeping water primrose. These are non-native plants that have the ability to spread rapidly and displace a more natural flora leaving behind habitats and wildlife that are significantly poorer as a result.

The Plant Positive project will run for three years initially and is intended to start the strategic and sustained effort that will be needed to push back these species and recover lost habitats.

Control will be focussed on two main river catchments, the Medina and the Eastern Yar where Himalayan balsam, Japanese Knotweed, Creeping Water Primrose and Parrots Feather will be the targets for control. A watching brief will be kept on New Zealand Pigmyweed and Giant Hogweed.

Work started in summer 2012 in some of the areas worst affected by invasive plants and good progress has been made already. A combination of conservation volunteers and specialist contractors will continue to work with the Natural Enterprise team to permanently clear large stands of these plants and mop up smaller outbreaks and so gradually give the local environment a chance to return to more favourable conditions for biodiversity.

What are Non-Native Invasive Plants?
According to Defra, an invasive non-native species is ‘any non-native animal or plant that has the ability to spread causing damage to the environment, the economy, our health and the way we live’.

Here on the Isle of Wight, Plant Positive will be focussing on a hit list of the worst offenders but it is important to remember that not all non-native species are bad for our environment. Those that are have been listed under Schedule 9 of the Wildlife and Countryside Act 1981 and it is an offence to plant or otherwise cause these species to grow in the wild.

Himalayan balsam (Impatiens glandulifera)

Himalayan balsam has spread across the whole of the UK since it was first introduced to British gardens in 1839. The key to its dramatic success is its explosive dispersal from pods which can catapult seeds over a very wide area. Its large and impressive pink flowers are very attractive to bees and other pollinators so there is never a shortage of new seeds. So attractive is balsam in fact that it out-competes nearby native plants for the attentions of pollinating insects and so reduces their ability to spread only making its invasive tendencies worse! Himalayan balsam is an annual, dying back in winter to leave bare soil which can expose our river banks to erosion and flooding. While the plant may be popular with bees, it is potentially disastrous for river species such as the water vole; Hampshire and Isle of Wight Wildlife Trust are currently exploring the possible contribution that Himalayan balsam is making to the decline of this species on the Island.
Download an identification guide here Himalayan Balsam

Japanese knotweed (Fallopia japonica)

Image: GNNSS

Probably the best-known and most notorious of all the non-native invasive plant species, feared for its legendary ability to smash through concrete! Introduced by the Victorians, Japanese knotweed spreads rapidly, often along watercourses, forming dense thickets that shade and crowd out our native plants. In winter, it is still easily recognisable as it dies back to leave forests of brown canes. The plant spreads naturally via its rhizome but also by human action. The tiniest fragment of root or stem carried on machinery or footwear is enough to spark a new invasion. Like Himalayan balsam, Japanese knotweed contributes to the erosion of our river banks and can increase the potential for flooding. It is capable of causing significant structural damage in the places where it grows and can become a very serious problem for building and development projects. Early and repeated intervention to prevent the spread of this tenacious plant is essential in limiting the long term costs of eradication.
Download an identification guide here Japanese knotweed
Download the Plant Positive Japanese knotweed – guide to best practice resource

Creeping Water Primrose (Ludwigia peploides)


This species was introduced to the UK as an ornamental pond plant, but has proven to be incredibly invasive and left unchecked can block whole waterways and overwhelm native flora. It spreads mainly by plant fragmentation but also by seed and has caused significant environmental problems across Europe; it is now on the UK’s most-wanted list but fortunately it is still confined to a relatively few areas, making early eradication still feasible. It is easiest to spot in late summer when it produces bright yellow flowers floating on ponds; it can though be confused with other less invasive species and so identification by an expert may be necessary to confirm an outbreak. One way of removing it is by diving down to pull out the roots from the bottom of ponds and lakes, but this is a method probably best left to the professionals!
Download an identification guide here Creeping Water-Primrose

Parrot’s Feather (Myriophyllum aquaticum)


Parrot’s feather was first brought to the UK around 1878 as a useful oxygenator for ponds and water gardens. It has since spread into the wild largely through the thoughtless (and now illegal) dumping of domestic garden and aquarium plants. Parrot’s feather is well-named; its blue-green feathery fronds are distinctive and recognisable throughout the year growing in still or slow-moving flowing water. Though most garden centres are aware of the threat thanks to the Defra Be Plant Wise campaign, Parrot’s feather can however still be found, sold under pseudonyms. Like several of the plants covered by our project, it spreads in the UK by fragmentation rather than seed and can quickly fill a waterbody, overtaking our native aquatic plants and blocking streams, ditches and drains.

Download an identification guide here Parrot’s Feather

New Zealand Pigmyweed (Crassula helmsii


Also known as Australian Swamp-stonecrop, Pigmyweed arrived in the UK in 1911. Like parrot’s feather it was introduced as an oxygenating plant for ponds and wasn’t recognised as a serious threat until the 1970s. It reproduces from tiny stem fragments and can be submerged, emergent (at the edges of water bodies) or terrestrial, growing in and around ponds, lakes and slow moving water courses. Left to its own devices, it forms an impenetrable green mat, pushing out plant and animal species and damaging wetland habitats. Pigmyweed grows all year round and produces small white flowers from June to September.
Download an identification guide here New Zealand Pigmyweed

Giant Hogweed (Heracleum mantegazzianum)

This is the closest thing to a triffid on our list of invaders! Giant hogweed is enormous, much like our native hogweed but on huge scale; fully-grown plants can reach up to 5 metres (that’s over 16 feet)! Giant hogweed was first planted as a striking ornamental in formal gardens over 100 years ago and has been known in the wild for nearly as long. It can quickly dominate over our native flora, spreading by seed via wind dispersal and water courses. Once established, like Himalayan balsam and knotweed, giant hogweed can cause bank erosion and increased risk of flooding. It’s highly toxic and contact with any part of the plant can cause serious and recurring blistering of the skin.
Download an identification guide here Giant Hogweed

A full list of non-native invasive plants in the UK can be found online at Defra’s website Non-native species – Be Plantwise!.

We live on an island, the risk of new infections from the mainland is low (but certainly not negligible), and we are quickly learning exactly where our hit-list plants are to be found. For these reasons we have a real opportunity to bring the spread of non-native plants under control here on the Isle of Wight. Working together is essential if we want to eradicate the worst non-native plants altogether. If you are a landowner, a garden-owner, a garden centre owner, an angler, a parish council or just looking for plants for your fish tank, there are practical and helpful things that you can to do to help:

Be Plant Wise
Most important of all is simply being aware of the threat posed by invasive plants and knowing how to avoid contributing to their spread. Follow the advice set out by the national Be Plant Wise campaign:

  • Know What You Grow
    Making sure you choose the right kind of plants for your pond or garden is essential; there are plenty of choices of native oxygenating plants for ponds for example. If you do discover an invasive plant already on your land, it’s important to tackle it swiftly; this might mean hand-pulling and composting for some plants, others may need spraying by experts.
  • Check, Clean, Dry
    Anglers, boat-owners and river users can all help to stop the spread of invasive aquatic species (fauna as well as flora) by making sure to check, clean and dry their clothing and equipment.
  • Compost with Care
    Making sure you dispose of non-native invasive plants correctly will help stop them from spreading – dumping of these plants is an offence.

For more details on all the above visit DEFRA’s Be Plant Wise campaign

Please get in touch if you find any of the non-native species using the ID sheets above, by completing and returning this record sheet

You can also now help track down non-native invasive plant with the following apps both available on iPhone and Android:

PlantTracker – help combat the spread of the UK’s most problematic invasive, non-native plant species.
Aqua Invaders – a project seeking to determine the status of 26 aquatic, non-native species including 12 fish species.