Oh no, knot another weed!

In the 80’s, 90’s and noughties, when the author’s life was more ‘Reads Books & Deeds’ than ‘Weeds Roots & Leaves’, the nearest a property lawyer came to horticulture when acting in the purchase of a house, was to enquire of the seller’s solicitors if that large tree in the garden was the subject of a Tree Preservation Order. Since 2013 it is standard practice for the seller of a property to declare whether  Japanese Knotweed*, Fallopia japonica, is present on the property in the Property Information Form. This means that it is the seller’s responsibility to check the garden for this invasive weed and if it is present to provide a management plan from a professional eradication company. Once a buyer’s solicitor has noted the presence of the weed when checking the form, and has notified the lender, the latter is likely to seek assurance that it will be eradicated, in the form of a management plan, before agreeing to fund the transition. Failure to disclose the presence of Japanese Knotweed or the lack of a management plan will delay the sale and increase the cost of the buying process or, the worst case scenario, give rise to a potential misrepresentation claim.

How has a plant introduced from the Far East in 1825 as a garden ornamental, and praised by innovative William Robinson in 1879 as ‘one of the finest herbaceous plants in cultivation’, developed a reputation as a possible property deal-breaker? Had Japanese Knotweed confined itself to the garden, the story would have ended here, but it escaped from gardens to establish colonies beside railway lines, waterways, roadsides and on waste land. By shielding lower growing species from light with its dense canopy it obliterates local native vegetation and its fallen leaves form a dense mulch to suppress the growth of any incipient seedlings. In the UK it spreads not by seed but by a huge rhizome system, impervious to many herbicides and needing a saw to sever the rhizomes. I can understand why our gardening forebears liked this plant- it has an attractive and exotic appearance with up to 2 metre tall bamboo-like stems speckled purple, heart shaped leaves about 15cm long and sprays of small white flowers. It would fill a shady corner very satisfactorily were it not for its thuggish tendencies.

As well as competing with native species, it contributes to river bank erosion and increases the risk of flooding. In a residential or commercial property context, it can cause structural damage by forcing itself through paving and concrete foundations. Indeed under the Environmental Protection Act 1990 Japanese Knotweed is classified as controlled waste. This means that a property owner must prevent it from spreading into the wild and causing ecological damage. If it discovered on a property it does not have to be removed but the property owner can be prosecuted for allowing it to spread onto someone else’s property and will understandably wish to find a satisfactory means of control. The bad news is that such means are both drastic and expensive. A few examples follow:

• Spraying, over a course of at least three years, with chemicals that are approved herbicides, until the underground rhizomes become dormant.
• Burying the waste at a depth of at least five metres (!), having first sought the approval of the Environment Agency.
• Arranging for the waste to be carried off-site by a registered waste carrier to be taken to an authorised landfill site.

Needless to say,  bio-security precautions are essential when dealing with this species and tools, boots and gloves require thorough cleaning and disinfecting after handling Japanese Knotweed to prevent pieces of plant material escaping and forming a new problem-laden clump. One recommendation I have read for how to deal with Japanese Knotweed is to move house! In light of the issues I have mentioned during the conveyancing process this may be easier said than done.

Before I move onto a more positive member of the knotweed family, I have seen the damage that an invasive plant can do to a building. In this case not Japanese Knotweed but the Tree of Heaven, Ailanthus altissima, whose roots had penetrated the foundations of a local church at the point where the wall of the building met the neighbouring path. I saw the plant material growing between the floor tiles inside the church! The tree, which was beautiful but unsuitable for planting so close to a building, has now been removed, but only after a protracted negotiation with the local authority.

Japanese Knotweed is a member of the knotweed family, Polygonaceae, which also contains the genus Persicaria. I planted a species of this plant in my garden earlier this year and I believe it is Persicaria amplexicaulis, or red bistort, I rescued it (with permission) from the ‘muddy clumps’ heap near the gardeners’ bothy at Osterley, a sort of holding area where discarded plant material is put before the garden team decide whether to compost it or use it for propagation. Although it did not flower until September, it put on a lot of vegetative growth during the summer, and has withstood a couple of overnight frosts and is still going strong this first week of November. The Royal Horticultural Society describe the plant as a robust, clump-forming, semi-evergreen perennial. All good qualities but I anticipate it might one day grow too large for this small garden. In the meantime I shall enjoy its narrow spires of reddish pink flowers atop a crown of pointed mid green leaves measuring 25cm with a slightly puckered appearance.

I am charmed by the idea that Persicaria hails from the Himalayas and can imagine it forming an understorey for Rhododendrons and Camellias on the mountains’ lower slopes. Quite a leap to a suburban garden, but the same can be said for many of our now familiar garden plants which originated thousands of miles away. And it reassuring to know that not all the plants under the knotweed ‘umbrella’ create a headache for the conveyancer.

• Useful information about Japanese Knotweed and how to control it and dispose of it can be found at gov.uk and at RHS