Under The Radar: Buddleia and Bamboo (and why aren t mortgage lenders concerned about them?) Jim Glaister The Knotweed Company Ltd
Introduction Mortgage lenders are concerned about Japanese knotweed and its impact on the built environment. Stories about knotweed are a favourite of the media albeit usually in a sensationalised and often inaccurate form. Japanese knotweed can damage the built environment, usually by exacerbating an existing weakness (e.g. cracks, crumbling mortar, decaying tarmac, etc.) or by destabilising/lifting paving slabs, block paving, etc. In very specific circumstances, knotweed can actually cause damage to structures: - in enclosed spaces (after years of human inactivity) - where new structures are built over it But these cases are rare.
But why aren t mortgage lenders concerned about other species, such as bamboo and buddleia? Aren t they just as bad?
Bamboo Bamboo has seen its popularity as a garden plant rise since the 1990s. Plant a bamboo screen
Bamboo There are at least 1,000 species of bamboo. It s been claimed bamboo is the fastest-growing woody plant in the world. It is a perennial evergreen (although some species can be deciduous or semi-deciduous) and is a member of the grass family. It has a jointed stem (called a culm) which is hollow in most species and grows from rhizome. Bamboo is capable of generating new growth from rhizome fragments. Bamboo rarely flowers and in many bamboos, the interval between flowering can be decades. (Phyllostachys bambusoides, otherwise known as Japanese timber, takes 130 years to flower). Some species flower annually, but these are unusual. Many bamboo species will die off after flowering, though others will be temporarily weakened and eventually recover. The length of the flowering cycle means bamboo does not produce seeds very often.
Bamboo Bamboo can be divided into two categories, defined by their type of rhizome: clumpers and runners. Clumping bamboos ( pachymorph ) produce rhizome that grow only short distances each year. New shoots generally emerge in close proximity to the plant. The rhizomes are typically quite thick. New culms form at the very tip of the rhizome and curve upwards. In mature plants, the concentration of stems can be very dense. The most common clumping bamboos include Bambusa, Dendrocalamus and Fargesia.
Bamboo Running bamboos ( leptomorph ) can be highly invasive. The rhizome is typically thin in appearance, jointed and can reach considerable lengths. Some species are capable of producing rhizome growth of up to 6m per growing season, though distances of 1m to 1.5m are more common. New culms can emerge from anywhere along the rhizome. The most common running bamboos include Arundinaria, Phyllostachys, Pleioblastus and Pseudosasa.
Bamboo Culms grow during spring and early summer, reaching their full height within 2-3 months of emerging from the rhizome. During late summer and autumn, the rhizome mass expands in preparation for the production of next season s culms. New, larger stems are produced every growing season, increasing the plant s height until such time as it reaches the maximum it can achieve for the area and conditions it is growing in. Older plants grow at a faster rate than newer ones. Height and rhizome spread is dependent on several factors, including location, soil type, species, climate, availability of water and age. In temperate conditions, a clumping species such as Fargesia can grow 30cm to 1m in height per year on average, while a running species such as Phyllostachys can achieve 1-2m per year.
Bamboo Rhizomes are strong and not easily broken. The rhizomes are naturally shallow and can usually be found no more than 30cm beneath the surface, though the rhizome mass can be extremely dense. Many are visible above the ground, particularly in running species. If bamboo finds insufficient nutrients in the shallows, it can send rhizomes to a greater depth (up to 1m) in search of water. Bamboo roots are thin and fibrous and can be found to a depth of up to 1m.
Bamboo Bamboo rhizomes interact destructively with the built environment. Bamboo can lift paving, distort or penetrate soft or decaying tarmac and can find its way into a building if there is a point of access available. Bamboo has been found growing through stone retaining walls. Bamboo shows no respect for property boundaries. If running bamboo is planted along a fenceline and not properly contained, it will quickly spread into the adjacent property.
Bamboo
Bamboo
Buddleia There are around 100 species of buddleia, with the most popular being common buddleia (Buddleia davidii). Originating in Japan and western China, it was imported into the UK during the nineteenth century as a garden ornamental. Buddleia davidii was first recorded in the UK at Kew in 1896. Buddleia is very hardy and can tolerate almost everything (drought, coastal exposure and atmospheric pollution) except full shade. Between September and October, buddleia produces an abundance of long brown fruits that split to release between 50-100 seeds from each fruit. That s an average of up to three million seeds per plant, which are widely distributed by the wind or along waterways.
Buddleia On average, buddleia grows to around 2.5m to 3m tall and spreads to between 1.5m to 3m wide although larger sizes have been recorded. If left uncontrolled, buddleia can quickly come to dominate a site, outcompeting other species, and can often be found in derelict or run down areas.
Buddleia Buddleia is often referred to as the butterfly bush. This leads people to think it is good for the environment and local ecology. It provides an important source of nectar for adult butterflies, moths and other insects but cannot provide the rich variety of nectar to be found in naturallyoccurring wild flowers. It does not provide food for caterpillars. Butterflies need host plants that allow larval offspring to feed on. Where buddleia is allowed to dominate an area, important butterfly habitat is eliminated. This, in turn, affects nonbutterfly species (e.g. species of bird that feed on caterpillars).
Buddleia The Butterfly Conservation Trust issued a position statement in 2012 on the planting of buddleia. It concluded buddleia could be planted in domestic gardens if properly maintained to prevent the dispersal of seeds. Butterfly Conservation will advise against planting of Buddleia in semi-natural habitat re-creation schemes or in positions where it may be unmanaged and pose a risk to nearby wildlife habitats. At the SSSI Folkestone Warren site in Kent, the domination of buddleia has seen a marked reduction in the number of butterfly species to be seen on the site. when [buddleia is] the only plant you grow for butterflies, you're not going to have butterflies anymore. (Doug Tallamy, professor and chair of entomology and wildlife ecology at the University of Delaware, USA)
Buddleia The Butterfly Bush
Buddleia Buddleia is responsible for more structural damage than Japanese knotweed. Seeds can grow in the smallest of cracks, without access to soil. It is particularly damaging to the railway network, where it hinders maintenance and damages infrastructure. It weakens bridges, interferes with overhead powerlines and obscures signals. In 2010, a study produced by CABI (Centre for Agriculture and Bioscience International) estimated buddleia cost the British economy 961,000 per annum (Williams 2010). The Non-Native Species Secretariat has described the problems buddleia presents to the rail network as significant.
Buddleia
Photos supplied by Neil Strong, Network Rail Buddleia The hidden story
Comparison to Japanese knotweed Issue Japanese knotweed bamboo buddleia Invasive Yes Yes Yes Causes damage to buildings Causes damage to walls, pavements and other non-building structures Exacerbates but unlikely to cause Causes rarely Exacerbates yes Same or more damaging than knotweed? Spreads by regenerative rhizomes Yes Yes No Spreads by seed Not in UK Rarely Yes (lots!) Detrimental effect on biodiversity Yes Yes Yes Sale and disposal restricted by law Yes No No Yes Yes Yes
So it makes no sense that mortgage lenders are concerned about this:
But not about this:
Call to action 1. Educate mortgage lenders on the issues buddleia and bamboo cause 2. Encourage legislators to introduce restrictions in regard to their sale (and disposal, in the case of bamboo) 3. Educate the public on the dangers of planting these species in their gardens 4. Educate clients to take bamboo and buddleia seriously and to not ignore them 5. Use the media to encourage a change in perspective on these plants Embrace the commercial opportunities that success in achieving these aims would provide.