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How air plants could be a secret weapon in the race for greener cities

UPDATED: Native to the rocky cliffs and deserts of South America, the humble air plant might be the low maintenance but high impact way of greening (and cooling) our cities that we need. A Melbourne artist has been working with them for 20 years and found the support from a leading engineer on his journey.

About four and a half years ago, an ecological artist, an environmental scientist and a structural engineer decided to see how a crop of the super-hardy tillandsia plants – commonly known as air plants – might fare on the top of Melbourne’s 91-storey Eureka Tower.

Apart from the plants on the east side of the building that weren’t getting enough rain, the remaining air plant gardens are still very much alive according to the ecological artists and long-time tillandsia enthusiast, Lloyd Godman.

He says that in those four and half years they’ve been exposed to the elements and haven’t been touched.

Suspended on cages above the building to create lightweight vertical garden 300 metres up in the sky, these plants have survived some incredibly hostile conditions.

Godman told The Fifth Estate that metal out in the open environment can get to “incredible temperatures” – as hot as 85 degrees Celsius. The wind factor also kicks in at this height, which sucks the moisture out of the air and can kill many types of plants.

But this extreme environment isn’t unlike the natural habitat of the air plant on the high rocky cliffs and sandy deserts in South and Central America, he explains.

“A building is basically a rock cliff”.

To survive on rocky cliffs – and now skyscrapers – air plants have made some remarkable adaptions. The plants don’t need soil to grow. Instead, they attach themselves to rocks, trees, manmade structures and other solid forms.

Rather than sucking in nutrients from roots, the plants have little scales on their foliage called trichomes that can catch water and nutrients from the air.

They can generally survive in hot, sunny weather with minimal water from rain.

The Eureka Tower experiment is one of a series of trials that followed an air plant installation in 2013 as part of the Melbourne City Arts Grant Project.

The aim of the experiments is to test the ability of the air plants to survive in extreme urban conditions. Sites include Federation Square, NGV, the Monash Gallery of Art, Montsalvat, and the Essendon Airfield.

Arcadis technical director Stuart Jones is also a fan of air plants and loves their lightweight nature and their adaptability. While hard material such as zinc weathers or deteriorates as they age, these plants do the inverse of this and grow a new resource over time.

“The ability to layer them is wonderful – they don’t have to be a single layer,” Jones says.

The potential of air plants in the built environment 

Air plants are not exactly novel and have been a favourite of time-strapped gardeners for some time. But what Godman can’t quite work out is why no one is cottoning on to the benefits of air plants to green the built environment on a larger scale.

“We’re excited about the potential of it and the positive effect it can have on the built environment.”

Many Australian cities are looking to insert more foliage into the urban environment, recognising the wellbeing benefits of greening, the ability of green space to cool cities, and the contribution plants can make to mitigating the impacts of climate change. Plants also help to purify the air of pollutants.

This has spurred the rise of vertical gardens on buildings. Although they look spectacular and have a number of environmental and health benefits, both Jones and Godman are sceptical of their practicality in some situations.

Maintaining vertical garden walls on high rise buildings can be expensive, Godman says. The cost of maintenance is rarely revealed but he has spoken to facility managers who claim to be “up on the cherry picker” attending to the gardens every second month.

Air plant gardens tend to cost about the same as normal vertical gardens – roughly $1000-$1200 a square metre – but once they are in place “we have pretty much proved you can leave them there and forget about them.”

There’s also no risk of damaging surrounding building infrastructure, with the irrigation systems in soil-based vertical gardens in danger of leaking into the building if not installed and managed correctly. Some plant varieties are also capable of growing through some building materials, but air plants are not.

Godman says there could also be a risk of fire with some typical vertical gardens because of the plastics many of them contain and how they’ve been designed, which has the potential to result in a similar situation to flammable cladding that has caused fires. He says there’s been two fires involving vertical gardens, one in India and one in Australia.

And tillandsia, like all plants, help clean the air of pollutants. They also are capable of purifying the air while we sleep because they photosynthesise at night, absorbing carbon and heavy metals from the air.

Air plants can be fixed to materials such as stainless steel and aluminium, meaning no plastics are used that end up polluting the environment at the end of life.

Normal vertical gardens are also heavy – weighing as much as 90 kilograms a sq m. But air plant gardens can be as light as five kilograms a sq m.

This means they can be attached to 3D objects and then moved around and suspended. Godman has created air plant sculptures that move around in the wind, as well as suspended structures that can be moved across windows or skylights to mitigate heat in summer then moved to allow light and heat in during winter.

He says shadows from the plants can reduce the temperature by as much as 30 degrees Celsius, making the suspended structures useful for intermittent shading above schools or other public spaces.

“You could have screens over airconditioning systems and other electricals, and the cooler you keep those systems the more efficiently they work. If you can drop the temperature back by 30 degrees, the efficiency gains are huge.”

“You could even have screens around solar storage systems.”

The engineers like it

The structural engineer who has been working with Godman on some of the air plant projects, Arcadis technical director Stuart Jones, likens these moveable air plant structures to “outdoor curtains” that can be moved across windows at night or when it’s hot.

He also likes their suitability for use in different visual layers.

“For instance, the façade at Federation Square, Melbourne, is a mixture of stone and metals. Just as zinc weathers or deteriorates over time, these plants do the inverse of this and grow a new resource over time. The ability to layer them is wonderful – they don’t have to be a single layer,” Jones says.

“Façades can be built up from a number of different layers and those living layers can be turned on or off, one passive the other active as needed.

“The other exciting aspect is that you can create depth on a building façade it does not have to be a flat surface.

Jones and Godman have lodged a proposal for an air plants structure on a library in Docklands, Melbourne, that will move up and down according to variations in the ocean tide using levers in the water.

Governments should become air plant advocates

Jones told The Fifth Estate that he thinks air plants have serious potential and is urging governments to use them in their urban development projects to set an example for industry to follow.

He also says that although sustainability is now on the agenda for most governments, it’s often talked about in a “superficial” or “tokenistic” way. When it comes to greening the urban environment, for example, he believes “we are still a long way off” and are yet to have started doing this in a sophisticated manner.

A better approach would be adopting lifecycle analysis principles “in everything we do”, he says, which would help stop “a lot of the things that they think are sustainable having a perverse effect”, such as ill-conceived urban greening projects.

Not all smooth sailing for the air plants

Godman is quick to admit that not every experiment has gone smoothly. The plants have been killed by extreme frosts and fail to thrive in some conditions. He believes air plants deserve more attention from people looking to green the urban environment but does not suggest they will be suitable in every situation.

“It’s about understanding what will grow successfully where,” he says.

“In Brisbane, you can grow heaps of species, in Melbourne you can’t grow heaps of species.”

He says although some purveyors of vertical gardens “pride themselves on having 300 species in the wall” they don’t always realise that “these are extreme environments.”

“And if it’s extreme you might only find five species, you don’t find hundreds of species on extreme places like rocky cliffs.”

He suspects one of the reasons air plants are not yet popular is their silvery colouring – “people want green foliage rather than silver, that’s one of the negatives. But that’s what makes them work, that’s how they’ve evolved.”

They are also quite slow growing at first but once they’ve matured and flowered, the plants double in size every year or two. They then can be harvested and moved elsewhere or even sold, he says.

Godman says that it takes as long as decades for the plants to grow so thickly that they become heavy enough to be a hazard on structures, but some harvesting is periodically required.

Stuart Jones added that because these plants are so rare and subsequently expensive, any maintenance costs from harvesting them are usually offset, or even surpassed, by selling them on.

“In any serious application they should be treated as a bio resource.”

Air plants are also unbothered by salt, which artist Lloyd Godman decided to demonstrate by attaching an air plant to his helmet and entering the surf. He says the plant is still very much alive.

20 years with tillandsias

Godman first started working with the plants 20 years ago, making small-scale sculptures in art galleries. After some time, he thought “why not put them on buildings?”

“That’s a far more exciting and beneficial thing to do.”

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Comments

7 Responses to “How air plants could be a secret weapon in the race for greener cities”

  • Kyoko says:

    Thank you for such an informative article. I wish this kind of air plant curtain is more widely available. It would be great to have air plant structure to be installed in public spaces. It would make beautiful and also functional spaces. It can be very educational too. I’d love to see Lloyd’s air plants making a big roof structure in Federation Square!

  • Matt says:

    I’ve had the joy of collaborating with Lloyd on several plant projects, and seen firsthand the resilience and adaptability of these amazing plants, and they are ideal to use in truly sustainable artistic projects.

  • Sharee says:

    As a botanist I think air plants could play a wonderful role in any built environment they are capable of living in. Their ability to cool and clean the air and provide habitat and nectar to birds and insects in our cities (which are often concrete jungles) can only be a bonus as far as I can see. I was delighted today to see one of our native Blue Banded bees go to a little purple/blue Air Plant flower.

  • Lloyd says:

    Thanks for the comment about your concern of these plants becoming weeds. To date no Tillandsias have been classified as weeds in Australia. Plants in any urban situation need to maintained.The key factor is the cost and regularity of the maintenance. It is important to remember that the impetus that drives all plants is to occupy areas of the planet- and many plants occupy areas of the built environment, so if you look hard enough you can see plants can turn up in strange places within any city.

    However the CAM cycle, water and nutrient uptake of Tillansias means they grow very slowly and any wild seedling Tillandsia plant would take at least a decade to grow into a small mature plant. In some parts of South America Tillandsias naturally germinated on power wires and over more than 50 years became so heavy that they had to be removed. This is less far less expensive than cutting branches from trees around power wires.

    However these potential issues should be set against the high maintenance that most vertical and roof gardens require. Vertical gardens like the spectacular One Central Park in Sydney have full time gardeners constantly attending to the wall and can cost many hundreds of thousands of dollars to maintain a year.

  • Geoff Beech says:

    As someone who has been growing tillansias in Melbourne for many years I can tell you it’s very hard to get their seed to germinate outside of a controlled environment and vegetive reproduction is extremely slow making them easy to manage and no risk to the environment at large . I think they could make a great contribution to greening difficult urban environments

  • Evie says:

    just wondering if you have assessed the potential for these species to become environmental weeds, particularly given their ability to withstand extreme conditions. It sounds like a great idea, but hopefully doesn’t create a different environmental impact, whilst helping address another.

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