How a purple, building eating plant is devouring Glasgow landmarks

The invasive shrub, with its thick foliage and bold bright purple flowers, is said to be growing uncontrollably across the city: bushes can be seen sprouting from even well-maintained building walls and roofs, it thrives alongside railway tracks and carpets entire derelict sites.

Buddleia sprouts in front of and on the A Listed Tobago Street Police Station (Image: Colin Drysdale)

However, a single plant can generate around a million seeds, which are then blown into air and can nestle in tiny cracks in building mortar.

Once established, its fibrous roots system can creep deep inside a building causing irreparable structural problems.

The issue was highlighted when the 19th century India Building had to be demolished after the roof of the Southside property collapsed inward and significant movement was noted in the front façade.

The Bridge Street building, constructed in 1876 as a warehouse for stationers Robert McGregor, had been vacant for 25 years, and was heavily infested with buddleia and other plants.

From Barrowlands Park across London Road, where this one buddleia plant is capable of producing up to one million seeds per year. (Image: Colin Drysdale)

The loss of the treasured building has ignited calls for a multi-agency approach to urgently tackle the risk the plant poses to the city’s built heritage from the plant.

Deirdre Molloy, chair of South Glasgow Heritage and Environment Trust said: “You can see it everywhere in the city. It is now ubiquitous because it produces so many seeds.

“It can take root in a bit of loose mortar. It can be seen coming out of roofs, even ones that don’t necessarily need an awful lot of maintenance, or from the side of a wall that seems otherwise quite well maintained.

Concern over the impact of buddleia was sparked by the demolition of the India Building (Image: Colin Drysdale)

“Each plant at maturity can produce one million seeds, and there must be billions of seeds blowing around Glasgow.”

Seeds can rest for up for four years before they start to grow, meaning many buildings may be already harbouring future problems.

“In Glasgow it is more magnified here because of levels of decay and levels and post-industrial landscape,” she adds.

“Southside landmarks are being colonised – it is a serious problem.”

Category-A listed Waverley Picture House with buddleia growing from a side wall (Image: South Glasgow Heritage and Environment Trust)

Buddleja davidii is native to Sichuan and Hubei provinces in central China and Japan and was brought to Britain by plant collectors in the 19th century.

It is often sought by gardeners who are encouraged by claims of its ability to attract butterflies.

However, it needs careful control: its millions of seeds can easily be carried on the air and come to rest in tiny cracks in masonry or on roofs.

It often colonises entire derelict sites leading to ‘buddleia farms’ which then spread seeds to neighbouring buildings.

But while buddleia, which can grow up to 15ft tall, is classified as an invasive species there is not the same focus on its removal as tends to be on other invaders such as Japanese knotweed, Rhododendron ponticum or giant hogweed.

Carlton Place (Laurieston, in the Gorbals) one of the last Georgian terraces to survive in Glasgow, with buddleia infestation (Image: South Glasgow Heritage and Environment Trust)

Ms Molloy has described it as “a wolf in sheep’s clothing”, portrayed as having benefits to biodiversity. But, she adds: “We only ever see nice photos of it surrounded by butterflies.

“Even the gardener who doesn’t mean any harm can be contributing to the problem.

“We would like to see very clear guidance on how ordinary people can deal with it. They need to know they have to cut off the flower heads before they dry out.

“There is not focus on its ability to outcompete surrounding plants and flowers and to spread.

“It reduces biodiversity and creates a monoculture. It is actually damaging biodiversity.”

Buddleia roots emerge from Caledonia Road Church (Image: South Glasgow Heritage and Environment Trust)

She says important buildings are coming under siege including the Waverley Picture House on Moss-side Road in Shawlands, where it’s seen sprouting from side walls and the roof.

It is also prevalent at Caledonia Road Church in the Gorbals, where the A-List Alexander Thomson building has buddleia rooted in the walls at its base which could eventually pose risk to the structure.

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The Georgian terraces of Carlton Place in the Gorbals, with A-Listed Lauriston House at their centre, are also affected.

Photographs showing buddleia encroaching on Glasgow’s derelict sites and taking root in buildings have been shared with the Trust on Twitter/X using the hashtag #buddleiawatchglasgow.

They include St Vincent Street Church, the former Dunnes Store on Sauchiehall Street and even the City Chambers with buddleia, all with buddleia sprouting from masonry.

A buddleja bush growing out of a wall round the Necropolis, showing the damage its roots can do to stonework (Image: Colin Drysdale)

Colin Drysdale, who photographs urban Glasgow scenes and whose images of buddleia helped spark the latest calls for action, said: “I photographed the India Building a few years ago and saw it had a lot of buddleia growing on it, but like a lot of people at the time I didn’t think too much about it.

“When the building had to be demolished, I was horror-struck. Suddenly it became clear that this stuff is destroying buildings.

“It’s not just unsightly, it’s causing huge structural problems, and something needs to be done about it.”

His recent photographs show buddleia taking over, among others, the C-listed former police station on Tobago Street and the former Golfhill Public School, which is heavily infested with the plant.

Derelict sites have become havens for buddleia (Image: Colin Drysdale)

He adds: “There are other much better native plants which do little or no damage to buildings and provide better support for urban biodiversity.”

A spokesperson for Glasgow City Council said: “Buddleia/vegetation growth on heritage buildings has been a problem for a very long time, and it is a symptom of a lack of maintenance that is an ongoing issue across all types of building. The issue becomes more serious when there is a lack of maintenance when an asset is vacant. The responsibility for maintenance and repair of any building rests with the owner/s.

Buddleia has taken over parts of Golfhill Public School (Image: Colin Drysdale)

“The council’s Planning team has written to owners in the past to remind them of this responsibility, highlighting vegetation growth if present and the benefits of removal, and the team will continue to do this as appropriate.

“We do appreciate that the funding the work to undertake vegetation removal and other maintenance can be challenging for some owners.”