A little-known ‘bombsite plant’ can wreak havoc on homes by forcing apart brickwork, chimneys and even roofs, experts have warned.
While Japanese knotweed has earned a reputation for damaging properties, specialists say buddleia, also known as the butterfly bush, can be just as destructive when left unchecked.
The fast-growing shrub earned its nickname after carpeting bomb sites across Britain following the Second World War, due to its ability to thrive in the tiniest cracks in walls and buildings.
Now, invasive weed specialists are urging homeowners to tackle the non-native plant before it causes costly structural damage.
According to government estimates, buddleia costs the UK economy around £961,000 per year in damage and control measures.
‘Buddleia is extremely opportunistic. Seeds germinate in tiny pockets of accumulated dust and organic material,’ said Jennifer Holmes, from invasive weed specialists Environment Controls.
‘As the plant matures, its roots expand into existing cracks, while the woody stems increase in diameter. This combination can force apart loose masonry, accelerate frost damage and increase water penetration.’
While buddleia is already widespread across Britain, certain parts of the country including London and the North West have higher concentrations of the shrub. To check your area, zoom in on this interactive map where darker areas indicate a higher quantity of reports.
The green areas on this map represent locations where buddleia has been reported. The darker areas show places with higher concentrations of the shrub
Buddleia, also known as the butterfly bush, can be just as destructive as Japanese knotweed when left unchecked
Unlike Japanese knotweed, which spreads through rhizomes – underground stems – a single mature buddleia plant can release up to three million lightweight seeds every year.
Carried by the wind, the seeds lodge in crumbling mortar, guttering, chimney pots and roof spaces, where they need very little soil to germinate.
As the roots expand, they act like wedges, prising apart existing cracks in brickwork and masonry, which in turn allows water to penetrate the structure.
Experts say this can loosen bricks, accelerate frost damage and even destabilise neglected walls over time.
Despite the risks, buddleia is not classed as an invasive species under Schedule 9 of the Wildlife and Countryside Act, meaning it is still legal to buy and sell in UK garden centres.
Ms Holmes said buddleia flowers usually bloom between June and October, making now a good time to check if there are any in the vicinity of your home.
It has purple, pink or white flowers, typically with orange centres, with ‘flower spikes’ up to 10in (25cm) long growing at the ends of its branches.
Young buddleia stems are green, while older stems have peeling, grey–brown bark. Its leaves are long and narrow and arranged opposite each other on the branches.
Experts say the plant can wreak havoc on homes by forcing apart brickwork, chimneys and even roofs
As the roots expand, they act like wedges, prising apart existing cracks in brickwork and masonry
Unfortunately, simply chopping the shrub down is unlikely to solve the problem.
The plant often regrows from its extensive root system unless it is treated with herbicide or is dug out completely.
Ms Holmes urged householders to inspect rooflines, chimneys and external walls during the summer, when the plant’s distinctive purple flowers make it easier to spot.
Warning signs include shoots emerging from brickwork or guttering, crumbling mortar around the plant and fresh stems sprouting just weeks after it has been cut back.
‘Without management, small plants can quickly become large shrubs several metres tall,’ she said.
‘Environment Controls has worked on contracts where buddleia has grown out of roofs (even multi–storey buildings), drains, brick walls and even alongside a railway platform.
‘We’ve even seen it growing through the structure of a boat.’
The company says the ideal time to tackle buddleia is from summer through to late autumn, when the plant absorbs herbicide more effectively.
It has purple, pink or white flowers typically with orange centres, with ‘flower spikes’ up to 10in (25cm) long growing at the ends of its branches
Environment Controls has found the plant growing on multi–storey buildings, alongside a railway platform and even through the structure of a boat
Ms Holmes said: ‘Many people search for DIY options and ask if buddleia can be killed by cutting it down.
‘But simply cutting the shrub to ground level rarely provides a permanent solution because regrowth commonly occurs from the remaining root system.
‘Professional control usually involves chemical treatment or digging it up. The most appropriate solution depends on the size, location and future use of the site.
‘If buddleia is growing on your property or development site, don’t wait for the damage to worsen, get rid of buddleia before it gains control.’
