Invasive weed specialists are warning homeowners about buddleia, also known as the butterfly bush, saying the fast-growing shrub can cause structural damage to properties comparable to Japanese knotweed when left unchecked.
The plant earned the nickname “bombsite plant” after spreading across bomb sites throughout Britain following the Second World War, owing to its ability to take root in the smallest cracks in walls and buildings.
According to government estimates, buddleia costs the UK economy around £961,000 per year in damage and control measures.
How it causes damage
Jennifer Holmes, from invasive weed specialists Environment Controls, said buddleia is extremely opportunistic, with seeds germinating in tiny pockets of accumulated dust and organic material. As the plant matures, its roots expand into existing cracks, while the woody stems increase in diameter, forcing apart loose masonry, accelerating frost damage and increasing water penetration.
Unlike Japanese knotweed, which spreads through 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.
Experts say the expanding roots act like wedges, prising apart cracks in brickwork and masonry, allowing water into the structure, loosening bricks and potentially destabilising neglected walls over time. Holmes said Environment Controls has worked on contracts where buddleia had grown out of roofs on multi-storey buildings, through drains, brick walls, alongside a railway platform and even through the structure of a boat.
Legal status and identification
Despite the risks, buddleia is not classed as an invasive species under Schedule 9 of the Wildlife and Countryside Act, meaning it remains legal to buy and sell in UK garden centres.
Holmes said buddleia flowers bloom between June and October, making the current period a good time for homeowners to check for the plant near their property. It has purple, pink or white flowers, typically with orange centres, with flower spikes up to 10 inches long. Young stems are green, while older stems have peeling grey-brown bark, and its leaves are long, narrow and arranged opposite each other on the branches.
Treatment advice
Holmes said 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 the plant out entirely.
The company says the ideal time to tackle buddleia is from summer through to late autumn, when the plant absorbs herbicide more effectively. 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.
Holmes urged homeowners not to wait for damage to worsen before taking action.
