How to turn a roof into a garden – successfully

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How to turn a roof into a garden – successfully

By Megan Backhouse

To look at Andy Beales digging up Jerusalem artichokes and weeding around kale you wouldn’t think he was pushing boundaries. Like any sensible food grower he is shredding garden waste to speed up his composting and laying down straw to encourage worms. His shovel and wheelbarrow sit at the ready. But here’s the thing that I haven’t yet mentioned: he is on a roof – the roof of a suburban shopping centre, no less.

“It’s not like a normal farm where you can just whack in a star picket to make a climbing frame for your tomatoes,” Beales says. “If you want to bring in a cubic metre of compost, you’ve first got to think about the capacity of your goods lift.”

Farm manager Andy Beales tending the roof of the Burwood Brickworks

Farm manager Andy Beales tending the roof of the Burwood BrickworksCredit:Eddie Jim

A normal farm this Burwood Brickworks rooftop might not be but it is a sign of what farms might yet become. As for what public parks might become, look no further than the manicured shrubs and timber day beds nestled in the sky between office towers in Collins Street. At the “Skypark”, the lawn is so green and so perfectly uniform that, when I visited this week, I had to touch it to check it was real.

Both these green roofs are mentioned in the new Maintenance Guidelines For Australian Green Roofs, which refocus our attention on an age-old idea that, after about a decade of active research, is starting to get a new foothold in Melbourne.

Productive green roofs, such as the Burwood Brickworks urban farm, have very high maintenance requirements

Productive green roofs, such as the Burwood Brickworks urban farm, have very high maintenance requirementsCredit:Eddie Jim

In the face of climate change, the biodiversity emergency and increasing urban density, green roofs can help make cities less destructive and more climate-resilient. They are cooling and biodiversity increasing. They reduce stormwater run-off, improve air quality and provide people with the pure pleasure of vegetation.

But only if they are well managed. Ignore them and they are doomed to failure. You might say this is true of every garden. But it is especially the case with landscapes on roofs, where almost nothing comes about by chance.

Green roofs are engineered “systems” with specially designed waterproofing, protection and drainage layers. The plants are growing in carefully concocted substrates applied at specific depths. The plants themselves are chosen to ensure they can cope with conditions off the ground.

The new maintenance guidelines, written by the University of Melbourne’s John Rayner, Elspeth Lumsden and Rachael Bathgate, detail how to manage all this in the local climate.

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They discuss the need for safe access, for ensuring all the different green roof layers remain intact and for managing effective irrigation and drainage. They emphasise the importance of understanding how plants – including weeds – behave differently on roofs compared to the ground.

Some of this is as simple as maintaining adequate substrate depth and not using hand tools with sharp points or edges that might pierce underlying layers. Some things – like cutting back plants that start to overly dominate – are similar to what you would do on the ground. But other tasks, such as removing woody weeds that develop potentially damaging taproots, can take on new urgency.

The key is to nail down how you will tend the roof from when it is first being designed, and then to stick to the schedule and also monitor the space regularly. While the guidelines, which can be downloaded for free, are largely aimed at those in planning, design, maintenance and management roles, they are relevant for anyone thinking about installing vegetation on the roof of their own home.

Brod Street first established a green roof on his Hawthorn house about 10 years ago

Brod Street first established a green roof on his Hawthorn house about 10 years agoCredit:Megan Backhouse

Although there have always been enthusiasts like Brod Street, who, about a decade ago conducted his own research and installed a beguiling grassland on top of his 1890s Hawthorn brick cottage ­­­– then added a successful “wetland” in 2019 and then a high-yielding vegetable patch on top of his backyard shed in January this year ­– there are lots of potential pitfalls for the uninitiated.

Even for the experienced some green roofs are easier to manage than others. The guidelines detail how much more care is required for the sort of productive roof currently being tended by Beales at the Burwood Brickworks, for example, compared with a lightweight, restricted-access one predominantly composed of low-growing succulents. To guarantee success, it’s crucial to tailor the maintenance plan to the site.

“There have been some really sad disasters around Melbourne,” Rayner says. “I am a fan of green roofs but I am a fan of successful green roofs. There is no point installing these things if they are not going to be sustained successfully. These are living landscapes that need maintenance planned into their design and management.”

Maintenance Guidelines For Australian Green Roofs can be downloaded for free from girg.science.unimelb.edu.au.

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