The mile high club…
Would you like a bigger backyard or allotment? Do you live in a flat and dream of a high rise garden to call your own? You could increase the amount of green space in your life by extending your garden or allotment out over a roof. Be it the top of your tool shed or the flat roof on an extension, why not join the mile high club of gardeners who are greening the roofs of the nation? Join Helen Babbs from London Wildlife Trust as she discovers a whole new roof top world.
I recently moved to a lovely little first floor flat in Islington, north London where I’m lucky enough to have a garden. Well, a garden of sorts. A small door in my bedroom opens out onto a flat roof, my neighbour’s kitchen roof to be precise. The estate agent optimistically calls it ‘the roof terrace’ and it certainly has potential. In a city where having a garden feels like something of a luxury, I’m very excited to have a small slice of outside space to call my own. But what on earth can I grow on it?
What is a living roof?
A living (or ‘green’) roof is a vegetated roof or a roof with some vegetated spaces. So it could be anything from a balcony packed with pots and planters, to a fully living roof with a carefully constructed layer of substrate (a mix of aggregate and sand or soil) out of which plants grow.
Living roofs vary greatly – they can be designed to support low-growing mosses and sedums, wildflowers and grasses and even shrubs and trees. Everything depends on the type of roof in question. There are three basic types: extensive, semi-extensive (also known as semi-intensive) and intensive. These terms relate to the amount and kind of maintenance that each type requires, the depth of soil or substrate, and the type of plants the area will support.
A Living Landscape
Conservationists and environmentalists argue that protecting and increasing a network of green space across the UK is incredibly important, and the idea of creating a ‘Living Landscape’ is championed by The Wildlife Trusts. A Living Landscape would provide valuable habitat for species and vital breathing space for us humans as things hot up.
Design for biodiversity
A green infrastructure, following ecological principles that integrate nature into the design and management of green spaces, allows us to harness natural processes to help solve wider environmental problems.
One organisation that actively supports design for biodiversity and living roof creation is The Wildlife Trusts. London Wildlife Trust, for example, is campaigning to make our capital greener, encouraging Londoners to take gardens seriously and start gardening with climate change and wildlife in mind. They want gardens protected for wildlife and people, and those gardens lost to concrete and decking to be compensated for with living roofs and walls. London Wildlife Trust wants everyone to pledge to do one thing for wildlife this summer, perhaps creating a living roof could be your one thing?
How do I do it?
So you’ve decided that having a living roof is a great idea, but how do you get started? And most importantly for us kitchen gardeners, is it possible to grow produce in the sky?
Dave Richards is garden co-ordinator at Reading International Solidarity Centre (RISC) and he has created an edible roof garden amongst the chimney stacks of the town. His garden is living proof that it is possible to grow fruit, herbs and vegetables on a roof.
“The RISC garden is planted as a forest garden, modeled on a woodland eco-system with many different layers of plants and permanent ground cover to suppress weeds and conserve moisture”, explains Dave.
“The garden has a canopy layer of small trees, including pruned fruit trees, and a layer of soft fruit shrubs. There are herbaceous perennials like asparagus and globe artichoke, and ground cover like strawberries, herbs. Climbers do well, things like grape and kiwi, and roots and tubers, such as potatoes, work.
“Just like any other garden, what you can grow depends on meeting the needs of the plants – sun, soil conditions, nutrients and water. A living roof is a bit like container gardening. A limiting factor is the depth of the soil. The RISC roof garden has 30cm of soil which limits the natural tendency of plant roots to search out moisture. This has a bonsai effect but many fruit trees and bushes flourish even on this limited depth.
“Water is the other main factor. In dry weather the irrigation system is on every night and we use various water conserving techniques. Soft fruit does very well – raspberries, Japanese wineberry, gooseberries – as well as some of our more exotic fruit such as medlar and old varieties of apple.
“To maintain fertility, we have to feed the soil with an annual application of organic horse manure and occasional applications of ground volcanic rock from Scotland and ground seaweed, to replace minerals leached out by irrigation.
A huge hanging basket
All of this sounds great, but it sounds like a living roof could be high maintenance. Dave Richards says it needn’t be.
“The most common and cheapest is an extensive living roof which has about 4cm of substrate and drought resistant plants, like sedum. These only need irrigation in really severe drought, and they provide most of the advantages of a green roof – thermal insulation, reducing storm water runoff and providing habitat for wildlife.
“An intensively planted living roof (like RISC’s) has deeper substrate and so can support a wider variety of plants. The additional weight needs a more substantial structure and, depending on the planting, an irrigation system. A roof garden is like a huge hanging basket and can dry out very quickly. Ongoing maintenance depends on the kind of planting. Vegetable beds would need more time than a garden planted with predominantly perennial species.”
The edible roof garden
Creating a living roof is a definitely a challenge, but well worth the effort. However, do seek out expert advice before you start, depending on the size of your project you may need planning permission and the advice of a structural engineer – see roof resources for more information.
Creating an edible roof garden with pots and planters is easier and relatively cheap too, and I’m definitely going to transform mine into an idyll for both people and wildlife. I have planted a crop of peas and I’m pleased to say they are flourishing, as are my herbs.
As summer approaches it is a real pleasure to spend evenings out on the roof with my produce. From online chats with a green roof enthusiast in Australia, to useful tips like growing Jersusalem artichokes as a windbreaker crop from a gardener in Nottingham, I’ve found a whole roof top community of gardeners, keen to share their experiences. Why not give it a go?
© Helen Babbs / The Wildlife Trusts
First published in Kitchen Garden magazine July 2008