Troublesome triffids: How to get rid of Japanese knotweed

(Rex)

However, if you have only a small clump and don’t plan on moving any time soon, you could aim to get rid of it yourself, says RHS chief horticultural adviser Guy Barter. “It’s evil stuff. It’s a lot of work and not feasible if there’s a vast infestation, but you can dig it out with a spade.

“Because it’s classified as ‘controlled waste’, you can’t let any plant material leave the garden. So stack it up to dry on plastic or concrete and then burn it. Or put it in rubble bags and leave it to die for a few years to be sure.”

Barter suggests combining digging up the plant with a herbicide such as Roundup. “But if you’re organic, just dig it up.”

If knotweed is coming in from a neighbouring garden, he says to dig a deep trench on the boundary and line it with a strong root barrier. Try ecomerchant.co.uk for root block impermeable membrane, from £6.25 per linear metre. Knotweed is the most notorious but by no means the only plant likely to have Londoners tearing their hair out. Bamboo makes a great urban privacy screen, rapidly growing to 6ft.

But the roots of “running” varieties can travel 20ft, easily ducking under a fence or wall and popping up next door in the form of thick, spiky shoots. If you plant bamboo, make sure you choose one described as “clump-forming” so it doesn’t get out of control.

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If your neighbour’s bamboo is coming into your garden, talk to them about it first, suggests Barter. If they won’t remove it, you could offer to pay for a contractor to do it.

And if this doesn’t work, dig a trench at least 20in deep and line it with a strong root barrier. In this case, a nice clump of bamboo leaves between you and them might be a welcome thing.

To discover what knotweed looks like and for further good guidance for homeowners, visit: rhs.org.uk/advice

CAN I REMOVE JAPANESE KNOTWEED MYSELF?

So where did Japanese knotweed come from? How did it get here? Why is it a problem? These are questions that many people have been asking for a long time.

Japanese knotweed grows! It grows no matter how poor the soil is. It grows no matter what season we are in. It does not respond well to cutting, burning or many other “off the shelf” remedies.

In fact – pulling or cutting the weed from the ground can actually stimulate the growth of Japanese knotweed! If you would like to use chemical treatment – this is an option but will only work with repeat applications of multiple sprays – over several years!

If you have the time, the physical ability and the inclination, then following the strategy outlined below would advisable:

  1. You need to fence off any areas that are infected by Japanese knotweed – this needs to be at the very least 7 metres away from any surface growth.
  2. Have an area specifically to clean your shoes when immediately leaving the infected areas (to stop the spread of infection – remember knotweed the size of your fingernail can grow into HUGE weeds).
  3. Carry out your first initial spray with a glyphosate based weed killer such as “roundup”.
  4. Check your chemical spray for guidelines on how long is necessary for the infected area to be left after the initial spray – so that the knotweed can absorb the chemicals.
  5. Remove ALL surface growth to a height of 15 CM above the crown of the plant.
  6. Leave the cut down growth to dry in an area where it will be un-disturbed and in piles that will not contaminate other areas
  7. Burn\incinerate all of the surface growth that you removed
  8. Check Environment Agency web site for document entitled Management of Japanese Knotweed (by clicking here) and look at pictures of rhizome to enable identification.
  9. Excavate the surface crown (by hand) and all visible rhizome. Be aware that this could extend as deep as 2 metres underground and upto 7 metres beyond the surface growth.
  10. Dry all of the crown and rhizome material by placing on a sheet of polythene and make SURE that it is kept away from any moisture.
  11. Once dried – make sure to burn\incinerate all of the crown and rhizome within your infected area.
  12. You will need to then continue to check and monitor and potentially REPEAT all of the steps outlined above for the next FIVE years!

The above is by no means an exhaustive list. We can carry out all of this above and assure you that once the Japanese knotweed removal has been carried out – the knotweed will be gone.

We offer fantastic piece of mind with a warranty that backs all of our work – we will even re-visit the job periodically to ensure that your knotweed infestation has been eradicated for good.

​Contact us TODAY on 0800 689 4146!

For more details of our excellent warranty please click here.

Knotweed, Japanese

Ecological Threat

Knotweeds are capable of quickly forming dense stands where they can crowd out native vegetation. Thickets can clog small waterways and displace streamside vegetation, increasing bank erosion and lowering the quality of riparian habitat for fish and wildlife. Once established, these stands are very difficult to eradicate.

ORIGIN

Both species of knotweed were introduced into North America for ornamental use and for forage and erosion control in the late 1800s.

HABITAT

Forest edges, meadows, fields, floodplains, disturbed areas

Life Cycle

The stems can reach heights of up to 10’ (3 m) tall, with some records indicating they can grow to 13’ (3.9 m) tall. The older shoots tend to get woody near the base as they age. Flowers emerge in late summer as small white to offwhite racemes / panicles. Pollination is by insects, primarily by bees. The three-winged seeds (Calyx) were often thought to be sterile; however, a basic germination test in NH showed that 95% of seeds collected from various populations were viable, but not seen as a significant vector for its spread.

Seedlings often succumb to frost, desiccation, shade, predation and smothering. The rooting system, which is composed of numerous intertwined rhizomes that can grow up to 3” (8 cm) in diameter, is the primary reproductive propagule that enables it to quickly spread to new locations. The rhizomes have the potential to spread laterally 23 to 65 feet (7-20 m) away from the crown. Most also have a deep taproot.

Based on the extensive rooting system, the majority (2/3) of Japanese knotweed plants occurs below ground. It helps to ensure the plant will rebound if damage to the shoots occurs. In addition, perennating buds found on the root crown and along the rhizomes will also react to shoot damage, i.e. mowing/cutting, by sending up additional shoots along the root. This typically results in radial/clonal spread of the plant and increases its shoot density.

A Knotty Problem: Japanese Knotweed on neighbouring land

It is now almost impossible to borrow against land affected by Japanese Knotweed, even if it’s on a neighbouring site. This article covers what measures can be taken to force a neighbour to deal with removal of the plant.

A landowner or occupier is under a duty to prevent the escape of Japanese Knotweed onto adjoining neighbouring land. There is however no legal obligation for a landowner or occupier to inform anyone that knotweed is present on the land or any legal obligation to remove or treat it. There are however legal obligations in the disposal of knotweed off-site, or the burning, burying or treating of it on-site. In brief, these are as follows.

The Local Authority has some discretionary powers in dealing with difficult neighbours with knotweed on their land. The Local Authority can serve a Notice under Section 215 Town and Country Planning Act 1990 (“S215”). The first step is to complain to the Local

Authority about the affected land. The Local Authority would always encourage a negotiation between neighbours first before looking to serve a Notice. If the negotiation is not effective, the Local Authority will then consider all the local circumstances, such as the condition of the site, the impact on the surrounding area and the scope of their powers.

If the Local Authority decides that action needs to be taken, they will firstly threaten the S215 Notice on the landowner or occupier. If this does not have the desired effect, it is then at the Local Authority’s discretion whether they serve such a Notice.

A S215 Notice requires a landowner or occupier to remedy the condition of the land within 28 days, where in the Local Authority’s opinion; the amenity of an area (or adjoining area) is adversely affected.

During the 28 day period, the landowner or occupier can apply to the Magistrates’ court against complying with the Notice, on any of the following grounds:

  • The condition of the land is as a result from the ordinary course of events Requirements of the notice are excessive
  • Time for compliance in thenotice is unreasonable
  • The infestation does not dversely affect amenity

If the occupier fails to comply with the Notice, the Local Authority can:

  • Prosecute the landowner or occupier in the Magistrate’s court with a fine currently not exceeding £1000
  • Step in to undertake the necessary works and recover reasonable costs from the landowner or occupier

Furthermore, under The Anti-Social Behaviour, Crime and Policing Act 2014, the Local Authority or the police have the power to serve a community protection notice on an individual (or body if applicable) if they are satisfied on reasonable grounds both that the conduct of an individual / body:

  • is having a detrimental effect, of a persistent nature, on the quality of life of those in the locality
  • is unreasonable

This legislation does not however explicitly refer to knotweed however the powers are intended to be flexible and it has been suggested in Home Office information that it could be used against an occupier failing to clear knotweed.

If no action is taken by a local authority an individual or a body can activate a ‘community trigger’ to request that the local authority deal with a persistant or previously ignored anti-social behaviour problem, which could apply to knotweed.

An alternative option, that a landowner or occupier could take themselves, is civil proceedings. If knotweed were to spread onto neighbouring land, this might amount to a common law nuisance.

The test for private nuisance is as follows:

  • There must be damage, or interference with the enjoyment of a neighbour’s land
    • which must be substantial or unreasonable; and
    • which may arise from a single incident or state of affairs.
  • The claimant must have a direct interest in the land affected by the nuisance.

If successful, the following remedies are available:

  • damages to compensate for loss; and/or
  • an injunction to prevent the continuing nuisance and prevent recurrence.

For any queries on Japanese Knotweed or if you are affected by knotweed, please contact Samantha Leigh in the first instance and a member of the firm’s environmental team will be able to assist.

The content of this page is a summary of the law in force at the present time and is not exhaustive, nor does it contain definitive advice. Specialist legal advice should be sought in relation to any queries that may arise.

Japanese Knotweed and The Law

No
For the vast majority of sellers, the selected response will be ‘no’. The seller may add a caveat along the lines of: ‘as far as I am aware’ to a response of ‘no’. This may reflect the fact that knotweed can be hard to spot in its early stages and most property owners are not horticultural experts. However if a seller, based on the best of their knowledge, answers ‘No’, and it subsequently transpires that the plant is present, then the buyer may pursue the seller for compensation.

Knotweed Management Plan is Paramount

The presence of knotweed does not automatically prevent a mortgage from being obtained, with a case by case basis approach often adopted. Evidence of a suitable Knotweed Management Plan is paramount. Whilst it might be a shock to find out that the property you are trying to sell has knotweed, or indeed, the property you intend to buy is affected, there are treatments available to manage the infestation and the Knotweed Management Plan is the key.

Misrepresentation Legal Rights

When buying a house, the person you are buying from is required to disclose if the property is affected by Japanese knotweed. If you have bought a house that’s affected by Japanese knotweed, and you are able to show the seller knew about Japanese knotweed on the property, you can sue the seller.

Loss of Property Value

If a property is found to have an infestation of Japanese knotweed on their land or Japanese knotweed within 7 meters, it is extremely difficult to secure a mortgage against the property.

As a result, a property affected by Japanese knotweed, whether it is in their boundary or within 7 meters, loses value. This is called diminution of value. If you are successful in bringing a Nuisance Claim against a defendant, then it may be possible to include a claim for diminution of value in any settlement.

Professional Negligence

If you purchased a property and paid for a professional survey to be carried out and the surveyor did not pick up the presence of Japanese knotweed, you may be able to bring a claim against the surveyor for professional negligence. If you are able to show that the surveyor should have noticed the Japanese knotweed, you can make a claim.

Disposal of Japanese Knotweed

The Government website has guidance called “Prevent Japanese knotweed from spreading”. It states:

“You must dispose of Japanese knotweed waste off-site by transferring it to a disposal facility that’s permitted, e.g. a landfill site that has the right environmental permit.”

“You must prevent Japanese knotweed on your land from spreading into the wild and causing a nuisance. You could be fined up to £5,000 or be sent to prison for up to 2 years if you allow contaminated soil or plant material from any waste you transfer to spread into the wild.”

This means if you cut back knotweed or dig it up and take it to your local waste and recycling centre that does not have the right environmental permit, you could be fined or sent to prison.

The Government website continues to state:

“You must not:

  • dispose of Japanese knotweed with other surplus soil
  • sell soil contaminated with Japanese knotweed as topsoil

You can only reuse knotweed-contaminated soils after treatment, on the site where they were produced.”

At Japanese Knotweed Ltd, we are fully equipped and highly trained to deal with Japanese knotweed infestations. Our team of field technicians have the relevant qualifications and experience to treat Japanese knotweed in a professional and legally compliant manner. If you suspect you have knotweed on your property, call in Japanese Knotweed Ltd, your local knotweed experts today: 0333 2414 413.

Wildlife and Countryside Act 1981

The Wildlife and Countryside Act 1981 is the primary legislation which protects animals, plants, and certain habitats in the UK. It’s worth noting, however, that since the passing of this Act in 1981, there have been various amendments to the text of the Act and the species listed in the schedules. Find out more here.

Environmental Protection Act 1990

The Environmental Protection Act 1990 (EPA) is an Act of the Parliament of the United Kingdom that as of 2008 defines, within England and Wales and Scotland, the fundamental structure and authority for waste management and control of emissions into the environment. This Act governs the disposal of controlled waste, such as Japanese knotweed . Find out more here.

Environmental Protection (Duty of Care) Regulations 1991

This Act exists to ensure responsibility is taken by the producers of waste (such as Japanese knotweed) for managing their waste and avoiding harm to human health or environment.

The Act aims to reduce or eradicate harmful acts of waste crime, such as fly tipping. The Duty of Care incorporates a responsibility on anyone who produces, imports, carries, keeps, treats or disposes of controlled waste to ensure it is only ever transferred to someone who is authorised to receive it. Find out more here.

Know Your Facts

Japanese Knotweed Legislation

We all have a responsibility to prevent invasive weed species spreading, especially if we own land where it’s growing. Failure to do so could result in criminal prosecution through the Wildlife and Countryside Act 1981 (WCA), resulting in fines or imprisonment. There are several components of Japanese knotweed legislation that could affect you:

Invasive Weeds & Japanese Knotweed Legislation

Causing invasive weeds to grow…

Japanese knotweed disposal…

If you plant or cause a Schedule 9 weed to grow you may face a £20k fine or 6 months in prison. Normally, documented treatment with herbicide is enough to show adherence to the law. EPA 1990 classifies invasive plant species materials as controlled waste and puts a duty on persons producing and moving such waste. Therefore you can’t put such material in the bin, get rid of it with other waste or, fly tip it.

Annoying thy neighbour…

Treating invasive weeds…

If invasive weeds are allowed to spread and can be proved to be having a detrimental effect on others, a Private Nuissance Claim can be made or a Community Enforcement Notice can be placed on the offending land owner. That’s right, a knotweed ASBO! Herbicides come under the Control of Pesticides Regulations 1997 and COSHH regulation 2002. In particular, water pollution must be avoided and if applying chemical on or near water approval from the EA is reeded.

Selling a home with Japanese knotweed

When selling a residential property, the vendor has to declare if their property has been affected by Japanese knotweed through Form TA6. Since a property sale is a legal transaction, correctly advising buyers will avoid the legal action that often follows from a false declaration.

If any invasive weed is found on a site, it should be left undisturbed and advice should then be sought on the most appropriate method of control.
PBA Solutions is an Environment Agency licensed waste carrier, meaning we’re able to take Japanese knotweed waste to licensed landfill sites around the UK.

If you’re looking to buy or sell a property that may be affected by Japanese knotweed, call PBA Solutions on 0203 174 2187 or email [email protected]

Japanese knotweed (Fallopia japonica var. japonica) was introduced into Europe in the mid-19th century by Philipp Franz Balthasar von Siebold, a German botanist and physician living in The Netherlands. In 1850, von Siebold sent a specimen of Japanese knotweed to Kew Gardens in London and by 1854, knotweed had travelled as far as the Royal Botanical Gardens in Edinburgh. Just over 30 years later, in 1886, Japanese knotweed was found growing in the “wild” for the first time, in Maesteg, south Wales.

Now, the plant is found in over 70% of UK hectads – 10km × 10km grid squares used to measure animal and plant distributions – although it is worth noting that this does not necessarily indicate high abundance in all areas. It is also established across mainland Europe, North America and the southern hemisphere. This global spread is astonishing – particularly as, to date, it has only occurred via plant fragments (vegetative) and not from (viable) seed.

In the UK alone, it is estimated that controlling Japanese knotweed costs the economy around £170m every year. There are at least 15 different active control methods and herbicides used in the country, and an extensive control industry has built up around the plant.

But, until now, there has never been a study of the scale needed to truly test how effective these treatments are. They are being sold to home and land owners with no unbiased research to back up their worth. However, we have recently completed the largest Japanese knotweed field trial ever conducted globally, and working with academic and industry partners, found the best way of treating the plant long term.

Control not kill

The key to our approach was to understand the plant, in order to control it. Japanese knotweed’s ease of spread and rapid growth from a deep rhizome (root) system was initially prized for planting schemes. However, from an ecological perspective, these plant traits are precisely why it has become a huge problem for native biodiversity and, increasingly, wider society.

Rapid growth from early in the growing season (February onwards in the UK) excludes most native plants from well-established Japanese knotweed patches (known as “stands”). This is because the dense canopy of leaves shades out other species. This shading effect is amplified as insects do not graze on knotweed plants, and native diseases don’t keep the plant in check either. Knotweed also produces a thick leaf litter, and chemicals that inhibit the germination and growth of native plants. It dominates non-native habitats, displacing native plants and altering how local ecosystems function – for example, in soil nutrient cycling.

During our research, it became apparent that because a Japanese knotweed stand contains significant underground and spreading biomass, we would need to do large field trials, to reflect real world conditions. So, we set up 58 different 15 metre × 15 metre (225 square metre) field trial plots, located in south Wales (UK), and repeated each method three times in these areas.

Between 2011 and 2016, we tested all control methods and herbicides used for controlling knotweed in the UK, Europe and North America – 19 in all. This experiment continues to be unique in terms of scale, duration and scientific rigour. But it is plain to see why this research has not been conducted before – the commercial cost has been (conservatively) estimated at £1.2m. However, given the ongoing costs of managing knotweed in the UK, the value of the experiment is self-evident.

Our research has highlighted the most appropriate way to treat established Japanese knotweed stands and, surprisingly, a number of other methods which are poor or totally ineffective at field scale. We now know that glyphosate-based herbicides are significantly better than all other herbicide groups currently used for knotweed control, and that physical methods such as covering up and cutting down knotweed simply do not work. Importantly, we are not describing eradication (which is almost impossible to acheive), but rather a type of extended “dormancy” where the plant does not grow above ground.

Plot comparison, before and after treatment. © Advanced Invasives 2018, Author provided

Additionally, we have also found that understanding when to apply the herbicide by considering the biology of the plant, specifically the seasonal surface-rhizome resource flows, is critically important. From this, we have defined a new patent pending approach to Japanese knotweed treatment, The 4-Stage Model™, which links herbicide selection and application with the seasonal surface-rhizome flows in the knotweed plant.

We are now working to replace outdated guidance based on short-term experiments and anecdotal information. We’re discovering how best to tackle invasive plants in real world conditions, informed by the evidence of what actually works.

While we acknowledge the current political debate surrounding glyphosate use and licence renewal for this herbicide, the effective outcomes of using glyphosate-based treatment seasonally requires lower doses of herbicide across the whole treatment life cycle. It is also more sustainable than other control methods that do not work.

All in all, our ongoing experimental approach delivers a more affordable knotweed treatment that is also more environmentally friendly than traditional, blanket application of herbicides.

PCA Invades RHS Chelsea Flower Show

Japanese Knotweed Ltd is proud to be supporting the Property Care Association (PCA) at the RHS Chelsea Flower Show from 22nd to 26th May this year.

The PCA will be taking invasive plants to the RHS Chelsea Flower Show to drive an important message to visitors. They’re showcasing 14 of the good, the bad and the ugly invasive non-native plants, which are currently thriving in gardens across the country. Entitled the “The Enemy Within – Managing Invasive Plants”, the showcase can be found within the Discovery Zone in the Great Pavilion at the RHS Chelsea Flower Show.

Professor Max Wade, chair of the PCA’s Invasive Weed Control Group, said: “Despite having more than 100,000 different plants available to gardeners in the UK, there is still a thirst for novel species.

“… giant rhubarb was first seen outside of gardens in 1908 and it wasn’t until about the turn of the century that it became invasive, while Japanese knotweed took from 1886 to around 1940 to start its ascendancy.

“Based on this, we should consider that not only is tomorrow’s Japanese knotweed growing in gardens today, but we are busy planting the follow-on generation to perpetuate the process.

“The PCA’s Invasive Weed Control Group (IWCG) is the front line in combating invasive weeds in the UK and Ireland and recognises that prevention is a whole lot better than the large-scale effort needed to keep Giant hogweed, giant rhubarb and Japanese knotweed invasions under control.

“Part of the challenge is to spot those species that have the makings of a problem for future generations.”

Steve Hodgson, chief executive of the PCA, says: “We don’t have to allow invasive plants to become such a big problem if we act responsibly. Non-natives which find niches in habitats, tend to grow without competition.

“If we are responsible about how we manage what we’ve got, we should be able to avoid the problems we see with things like Himalayan balsam, Giant hogweed and Japanese knotweed.”

Plants on show include the following:

Buddleia (Butterfly Bush)

B. davidii is a multi-stemmed shrub or small-tree that is native to China and has been introduced as an ornamental world-wide, first to Europe (1890s) and then later to the Americas, Australia, New Zealand, and some parts of Africa. Since that time, B. davidii has naturalised within sub-oceanic climates in the temperate and sub-Mediterranean zones.

The full potential of this species has yet to be realised; however, it is already considered problematic (i.e. out-competing native, agricultural, and forestry species) in northwestern and northeastern USA and Canada, throughout New Zealand, and in central Europe. B. davidii is tolerant of a broad range of environmental conditions, capable of prolific seed production, grows rapidly, and has a short juvenile period.

Montbretia

Crocosmia x crocosmifoliawas was originally created in France from parent plants of South African origin and is easily recognisable when in flower by the distinct shape and colour of their flower heads.

Introduced to the UK in 1880 as a garden plant. It escaped by 1911 both naturally and through the disposal of garden waste, and spread rapidly across the UK in the latter part of the 20th century. Can completely dominate habitat where it grows, sometimes excluding native plant species. Spreads mainly by rhizomes, rarely by seed.

Montbretia is listed under Schedule 9 to the Wildlife and Countryside Act 1981 with respect to England and Wales. As such, it is an offence to plant or otherwise allow this species to grow in the wild.

False Virginia Creeper

Parthenocissus inserta is a deciduous perennial woody climber, native to North America, that grows prolifically to 15m or more. It climbs by means of small branched twining tendrils which may have swollen ends but lack the cup-like adhesive pads of the very similar-looking Virginia-creeper P. quinquefolia. It has stalked five-lobed leaves with toothed edges which turn crimson before falling in the autumn.

It is native to north America and was introduced to the UK as an ornamental climber before 1824 and first recorded in the wild in 1948. It is often confused with Virginia-creeper, which shares its vivid red autumn foliage and the ability to screen unsightly areas.

A mature plant will scale most trees and shrubs. This causes several problems; the climber prevents the host and other plants below from receiving sufficient light and may cause death. Additionally, the weight of the climber can contribute to branch breakage or canopy collapse and finally it can girdle trees, effectively slowly strangling them over an extended period.

Garden Lupin

Lupinus polyphyllus is a herbaceous tuft-forming perennial, with unbranched stems with alternate, pamate leaves with long petioles. It’s native to western parts of north America with an oceanic climate and was introduced to England in 1826. It can outcompete native species occurring in road verges, ruderal areas, gravelly floodplains and other habitats. Due to its nitrogen-fixing nodules, L. polyphyllus changes the soil chemistry and the consequent changes in community structure and diversity is the main problem when it invades and area.

Email: [email protected]
Phone: 0333 2414 413

Chelsea takeover: Japanese knotweed and other invasive plants to feature in this year’s Flower Show

PUBLISHED: 08:00 04 April 2018

Hannah Stephenson

The RHS recommends using a professional firm to eradicate Japanese knotweed (Credit: Environet/PA)

Archant

Non-native invasive plants are to feature in a show garden at this year’s RHS Chelsea Flower Show – so what are they and how can we control them?

Bamboo: “Watch it, manage it and if in doubt, remove it.” (Credit: Thinkstock/PA)

When we think of invasive plants, alarm bells might ring at the mention of Japanese knotweed or giant hogweed – but can the same be said about buddleia, bamboo or montbretia?

These – and other – common plants will be coming under the spotlight at this year’s RHS Chelsea Flower Show (May 22-26), in a garden of invasive plants, created to highlight non-native species that ‘escape’ from gardens up and down the UK and the damage they can do once let loose.

Steve Hodgson of the Property Care Association (Credit: PA/PA)

To raise awareness of the issue, experts from the Property Care Association’s Invasive Weed Control Group are developing the ‘Enemy Within’ garden to showcase 14 of the invasive non-native plants currently thriving in gardens across the country.

Professor Max Wade, chairman of the PCA’s Invasive Weed Control Group, says: “We know from studies of today’s invasive weeds that it can take decades to become a national problem after escaping from gardens.

Leave montbretia alone it will spread like wildfire (Credit: AECOM/PA)

“For instance, giant rhubarb was first seen outside of gardens in 1908 and it wasn’t until about the turn of the century that it became invasive, while Japanese knotweed took from 1886 to around 1940 to start its ascendancy.

“Based on this, we should consider that not only is tomorrow’s Japanese knotweed growing in gardens today, but we are busy planting the follow-on generation to perpetuate the process.”

Steve Hodgson, chief executive of the PCA, says: “We don’t have to allow invasive plants to become such a big problem if we act responsibly. Non-natives which find niches in habitats, tend to grow without competition.

“If we are responsible about how we manage what we’ve got, we should be able to avoid the problems we see with things like Himalayan balsam, giant hogweed and knotweed.”

Other plants that have the same potential include:

Bamboo

There’s been a lot of bamboo planted over the years, thanks to its popularity in gardening makeover shows and horticultural fashion generally, says Hodgson. If they are left unchecked they can be just as damaging as anything else. “Watch it, manage it and if in doubt, remove it,” he advises. “There are well-established professional organisations that can help if you can’t do it yourself.”

Buddleia

“We have a massive problem with the butterfly bush,” he says. “It’s a real nightmare. Anecdotally, it causes more structural damage to buildings than anything else. The fact is, if it is left close to buildings, the buddleia roots are so strong they will pull the masonry apart. It starts from a seed.” Plant a buddleia near to your home at your peril. If you see any seedlings which have taken next to the house, pull them out, he advises.

Montbretia

“Leave it alone it will spread like wildfire. In most domestic gardens it will out-compete the other plants in the flowerbed – and when you get it into a wild environment, it does exactly the same thing.” You can dig the corms of montbretia up to keep it in check – but don’t dispose of it on your compost heap because it’s likely that wherever you spread the compost, the montbretia will follow. One solution is to burn the corms, he says.

Aquatic plants

Pennywort and water fern are problematic, he says. Reports of the invasive plant floating pennywort in rivers and lakes have reached a record high, officials are warning. “They often arrive because somebody’s cleaned out a fish tank. They were imported and used in aquariums and fish tanks and people clean them out and chuck them into the nearest pond, and before you know it, they are filling up rivers and ponds. They do a huge amount of environmental damage.”

Japanese knotweed

This is a massive problem, because if you disturb it and then leave fragments under new structures, it will grow back through an extension or a patio or into a conservatory. The RHS has just extended its advice to include the role of professional firms to eradicate knotweed, warning that DIY attempts at treatment or removal may not be successful.

For keen gardeners who wish to attempt to treat or dig out Japanese knotweed themselves, the RHS warns the plant is very deeply penetrating and success is not assured. Also, it is classed as ‘controlled waste’ and therefore requires careful disposal at licensed landfill sites.

How do you get rid of the corms, runners and rhizomes of invasive plants?

“The biggest issue is to be really sensible about disposal. You can’t chuck this stuff in a skip because it will go to landfill and cause a problem somewhere else. Don’t put it into cold composting. You might have to burn it,” says Hodgson.

“The difficulty is the corms. If your garden waste bin goes to hot composting, that should be okay. But if you don’t know where it goes, think it through. Most skip companies will do it for you, but it is very expensive.”

Put invasive plants in containers

If you want these plants in the garden, put them in pots so they are contained, he advises.

“If you containerise plants which spread by runners or rhizomes, you will have a hugely restricting ability.”

He does not recommend strong weedkillers. However, advice generally given about getting rid of bamboo and other invasive plants involves using a combination of digging and using of the strongest forms of glyphosate available to gardeners.

For more information on the RHS Chelsea Flower Show, go to rhs.org.uk.

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