Invasive plants: European regulations

Seeds of doubt

29 March 2018

Increasing concern about invasive, non-native plants has prompted an expansion of European regulation. Max Wade and Mark Fennell look at the implications for surveyors

For most RICS members, talk of invasive weeds is likely to centre on Japanese knotweed. However, while this species dominates news coverage, there are many other invasive, non-native species of which surveyors should be aware, reporting them and advising clients or taking action as appropriate.

New and emerging species

Highlighting increasing concern about invasive, non-native weeds across the UK and beyond, the European Commission last summer added 9 more plant species to the 14 already covered by the invasive species regulation. These “invasive alien species of Union concern” have been selected following extensive risk assessment of their potential to cause negative impacts at a continental scale. As always, prevention, surveillance and rapid response are the best ways to prevent such impacts.

The additions are:

  • alligator weed (Alternanthera philoxeroides);
  • milkweed (Asclepias syriaca);
  • Nuttall’s waterweed (Elodea nuttallii);
  • giant or Chilean rhubarb (Gunnera tinctoria);
  • giant hogweed (Heracleum mantegazzianum);
  • Himalayan or Indian balsam (Impatiens glandulifera);
  • Japanese stiltgrass (Microstegium vimineum);
  • broadleaf watermilfoil (Myriophyllum heterophyllum); and
  • crimson fountaingrass (Pennisetum setaceum).

Descriptions of some of these and certain other plants already on the list are provided in the panel below.

The legislation that will place obligations on individuals, in the form of controls and penalties, is now in development. As such, landowners, their agents and chartered surveyors should be aware of the growing list of invasive species, and ensure they are prepared to act accordingly should an issue arise.

Present and future threat

The plants listed in the EU regulations can be usefully divided into 2 groups. The 1st comprises those present in the UK and Ireland that are recognised as weeds, and the 2nd comprises those that could become a threat in the future.

The new additions to the 1st group are Nuttall’s waterweed, giant rhubarb, giant hogweed and Himalayan or Indian balsam. Species that are either not yet present in the wild or very rare in the UK or Ireland, and thus in the 2nd group, are alligator weed, milkweed, Japanese stiltgrass, broadleaf or variable-leaf watermilfoil, and crimson fountaingrass.

There are different reasons for adding the various species to the list. Giant hogweed, for example, produces sap that is extremely toxic to the skin in sunlight, making it a danger to public health. Himalayan balsam and giant hogweed were added because they can take hold in areas such as along rivers and drainage ditches, impeding water flow during periods of high rainfall. Such growth in turn exacerbates flooding and can lead to erosion when the species die back in the winter.

Surveyors should be paying attention to all these plants, though for different reasons in each case. Giant hogweed, for example, should be removed from a property – ideally, before sale – because it is a health hazard, and prospective buyers ought at least to be made aware of its presence and the danger associated with skin contact. This could be an issue in areas where there is a high incidence of the plant, such as in parts of west London.

Should a property mark the first occurrence of one of the plants not yet found outside gardens, such as milkweed, then there could be an imperative from the government to eradicate it forthwith. This is likely to be the case on larger properties and land holdings.

Invasive species impacts

While the impacts of invasive plants are wide-ranging because they present risks to the environment, water utilities, transport infrastructure and even public health, it is the effect they have on property sales and mortgages that is the most pressing issue so far as surveyors are concerned.

There are many instances where, if Japanese knotweed is visible within 7 metres of a property, it has resulted in both land and property being devalued – even leading to the refusal of mortgages in numerous cases.

There are instances, too, where homeowners have had applications for loans or remortgages refused by lenders without the risk being quantified by a specialist. This goes against information and guidelines in the RICS Japanese knotweed and residential property information paper of 2012, and its 2015 addendum, to help surveyors and lenders understand the procedures to follow where that plant is found.

Landowner responsibility

A pair of recent, linked court cases have added a new dimension to the debate, placing responsibility for remediation and control of invasive species on the shoulders of landowners. The rulings in Robin Waistell v Network Rail Infrastructure Limited (2017) and Stephen Williams v Network Rail Infrastructure Limited (2017) ordered Network Rail to pay compensation for the loss in value caused to homes adjacent to its property, as it had not appropriately managed the Japanese knotweed on its land.

Despite the fact that no physical damage was caused, Network Rail was ordered to pay compensation along with the cost of treating the knotweed. These cases highlight how important it is for landowners to take responsibility for all infestations, particularly near houses and other property, as soon as they come to light. An appeal against the judgment in both cases is due to be heard in June 2018.

These cases could encourage more homeowners to take similar action, with respect not just to Japanese knotweed but also other scheduled species. As a result, surveyors should be aware that their role in promoting and implementing solutions may expand. Resorting to legal action is expensive, and it should not be underestimated how difficult it is to determine the origin of an invasive plant. Therefore, property owners should work together to deal with Japanese knotweed or other invasive weeds, while surveyors and contractors must be alert to the problem, promote vigilance, and advise and implement effective, proportionate solutions.

Reducing the risk

The emphasis of invasive weed control to date has been on controlling plants when they become troublesome. This is akin to closing the stable door after the horse has bolted, and typically involves re-treatment over a number of years. Organisations such as the Property Care Association (PCA) and the GB Non-Native Species Secretariat advocate preventative measures to stop the spread of these plants on to properties.

The key is to identify weeds’ pathways on to a property and shut them down. Surveyors should be aware their dirty footwear may be a route, transferring, for example, giant hogweed or Himalayan balsam seeds or fragments of Japanese knotweed, from an infested site to a clean one. The secretariat advises you always check, clean and dry your clothing and equipment.

Some species of EU concern

Himalayan or Indian balsam

Himalayan balsam



This tall herbaceous annual frequently grows on the banks of lowland waterways, often forming continuous stands. These can obstruct water flow during summer floods and leave banks exposed to erosion in the winter. The balsam out-competes native vegetation, although it is a good source of nectar for bees.

Giant or Chilean rhubarb

Giant or Chilean rhubarb


This is a huge, clump-forming perennial that is widely naturalised in permanently damp and shaded areas that have rich soil, including woodland and grassland near water. The plant is often self-sown where it is long established. Plants forms dense colonies of 0.5ha or more, suppressing native plants as the large rhubarb leaves prevent growth underneath. The species takes over hedges, roadside verges and ditches, and impedes water flow by obstructing streams and rivers when water levels are high.





This vigorous, soft, hairy perennial with fleshy roots and upright stems grows scented, greenish and purple-pink or occasionally white flowers in drooping umbel-like clusters during the summer. These are followed by pendant, softly spiny fruit with brown, flat seeds and a tuft of silky white hairs. In some parts of the world, it is an aggressive and persistent weed, containing substances known to be poisonous to sheep, cattle and sometimes horses.

Parrot’s feather

Parrot's feather


Parrot’s feather is an emergent and submerged perennial with long trailing stems of up to 2m. It is found in small, sheltered, nutrient-rich water bodies, especially ponds and ditches but increasingly in reservoirs, canals and flooded quarries. Dense growth can choke bodies of water and waterways, interfere with recreation and impede flow.

American skunk cabbage

American skunk cabbage


A perennial stemless, rhizomatous herb, this has leaves that grow up to 1.5m in length, although they are typically less than 1.2m. The species is increasingly found in parks and gardens and naturalised in wet ground, beside ponds and streams or in wet woodland. It persists and spreads and can potentially dominate large areas, out-competing native species. Sap from its leaves and rhizomes may irritate the skin and eyes, while all parts are poisonous and may cause severe discomfort if eaten.

Crimson fountaingrass

Crimson fountaingrass


Crimson fountaingrass is a mound-forming, densely tufted, deciduous perennial grass that often grows in gardens as an annual. From midsummer through to early autumn, the plant bears pink to purplish-pink plumed spikelets. Although it is not known outside cultivation in the UK and Ireland, it has invaded a range of different habitats in other parts of the world, sometimes forming monocultures.

Weed control operatives must be able to recognise the expanding list of species, including some not yet seen in the UK outside cultivation. Where a scheduled invasive, non-native plant appears on a property for the first time, landowners need to be able to implement a rapid response to eradicate it before it gains a foothold. Once they are well established, eradication becomes more challenging and costly, and the site and environs are vulnerable to further spread.

Coordinated approach

In 2012, the PCA worked with RICS, supported by the Council of Mortgage Lenders, the Building Societies Association and Japanese knotweed control companies, to set up the Invasive Weed Control Group (IWCG), whose membership has the expertise to control and manage invasive plant species.

We are taking steps to ensure Japanese knotweed and other invasive, non-native species are viewed just as any other type of property problem would be: one to be identified, risk-assessed and treated by recognised experts with minimal impact.

To maintain this professional approach, the PCA has produced a comprehensive code of practice for managing invasive plants, technical guidance notes, and training with associated examination and certification. It also organises an annual conference at which a wide range of property professionals discuss the latest insights on the issues associated with managing invasive, non-native weeds.

This approach to raising standards and encouraging best practice in the profession means that the PCA is well placed to deal with the challenges ahead, and can help surveyors navigate a subject that is growing in economic and environmental significance day by day.

Professor Max Wade is chairman of IWCG and Dr Mark Fennell chairs the IWCG Education Group

Further information