Gardens Illustrated
Tijana Blanusa
© Jason Ingram

Tijana Blanusa on green façades and the science behind the best hedging plants

Published: August 18, 2022 at 9:35 am
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The head of the RHS Ecosystem Services Research Programme, on identifying the plant traits that can benefit the wider environment and why you really need to plant a hawthorn hedge. Portrait Jason Ingram

Have you ever wondered which species might make the most superior hedge or what the best street tree is? Not just look good but mitigate against flash flooding or incept the most particulate pollution? Dr Tijana Blanusa has. She leads the Royal Horticultural Society’s Ecosystem Services Research Programme, which looks into the environmental benefits of gardens and green infrastructure. Her work is enabling us to understand the contribution plants make to our living environments. “It’s not just a tree in a city, it’s a cooling system,” she says. “It’s storing carbon, it’s reducing noise, improving air quality, increasing biodiversity. I am just fascinated by that, by how much a plant can do."

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I am just fascinated by how much a plant can do.

Tijana grew up in Belgrade, Serbia, and spent a lot of time in her grandfather’s garden. “When he retired he bought a plot of land, and took up bee keeping and tending an orchard,” she says. “One day he said: ‘Look I pruned this tree and there’s a half-kilo apple.’ It was really the biggest apple I’d ever seen and then he said, ‘And here is a tree I haven’t pruned,’ and pointed to one with much smaller apples. That really fascinated me as a kid, how you can manipulate a tree.”

Her fascination prompted her to study agronomy and crops science at university followed by a master’s degree in plant physiology, before moving to the UK to begin a PhD on how much a cherry tree can sustain in fruit. Then in 2003 she saw that the RHS was looking for a horticultural scientist. “I knew straight way that it was my job.”

The role, which has occupied her ever since, was conceived as a way to further links between the RHS and the University of Reading, where she’s based. There she teaches green infrastructure and supervises numerous students from undergraduates to PhD students, but also works closely with the RHS advice team, and with architects, planners and builders to help inform better planting choices.

“I like very practical science and I’m a stickler for a simple, cheap solution,” she says. For example, climbers such as ivy are good as a green wall in terms of their insulation properties, but can damage the building, which is why one of her students has looked into using anti-graffiti paint as a cheap solution to prevent ivy from attaching to a building. But the projects she’s worked on span everything from optimising water use in container-grown bedding plants to houseplants and their effect on our wellbeing and how we incorporate green infrastructure into our living environment.

I’m a stickler for a simple, cheap solution.

“When I did my first project on a green façade, I really had to justify why I was doing it, there were so few references. But the understanding has grown exponentially from then. There’s a real understanding that we need to incorporate plants into our urban planning and architecture,” she says. “Of course, gardeners understand this, but we need to expand that out into policy work. I mean people are putting in plastic lawns and plastic hedges!”

She knows there is much more to do and many more areas to look into. She’s curious about urban food production and wants to investigate the genuine impact of growing your own. “What’s the nutritional value, how much do you really have to grow to make an impact?” she asks. “Plus, there’s more work to do on green infrastructure, we understand a lot about what does and doesn’t work on a species level, but we need to look into planting mixes rather than monocultures; can we enhance the overall potential of a garden with the right mix? It’s so important to understand the details.”

There’s a real understanding that we need to incorporate plants into our urban planning and architecture.

Even so her research is already making a difference. “I’m humbled that the science I do has a practical impact. When someone comes up to me at a conference and says: ‘I saw one of your papers and we tried it out in our garden,’ then I’m very happy that I get to push our science forward.”

And if you’re still wondering what is the best hedge for reducing flooding, that would be hawthorn. It takes up a lot of water while in growth, and then transpires it, increasing the soil’s capacity to receive subsequent rainfall that could otherwise end up in drains. “When it’s physiologically active that plant just pumps up water. But it’s deciduous, so in the winter it’s not providing as much of a service, which is why we’re experimenting with the very best mix,” says Tijana. “Also Thuja plicata; it has the most amazing canopy storage, it holds on to the rain and funnels it down into the soil over a long period, so it’s really good for sandy soils. Canopy storage of water in constant drizzle can make a real difference.”

Her own garden, she admits, is an unplanned jumble of left-over plants from experiments – “I’m a plant scientist not a gardener” – but she does at least have a hedge. “It’s the only one left in the street. It looks lovely, I do very little other than cut it once a year.” Thanks to Tijana’s research we know that hedge is doing an awful lot of work.

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USEFUL INFORMATION
Find out more about the RHS’s science research at rhs.org.uk/science

Authors

Alys Fowler is a horticulturist, garden writer and Guardian columnist.

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