In the last 12 months, almost every time I have given a talk about green roofs in Australia, whether to the general public, property developers, facility managers, architects or local government teams, at least one person has asked, “do community garden green roofs work?”

There are several reasons why the question is arising now. First, as people in cities become more and more divorced from frequent interactions with nature and with farming, their interest in growing produce at home is increasing. Design professionals are, naturally, aware of their clients’ hobbies.

Second, Australian property developers and portfolio managers who are looking to differentiate themselves are taking an increasing interest in rating systems such as the WELL Building Standard, which assesses, among other factors, the quality of experience of any one building by its community.

Using the rooftop to host a garden which the building community cultivates in some kind of common space is thus an enticing notion. It seems an excellent means of meeting various planning requirements, achieving a high rating under WELL, and making use of an otherwise wasted space.

But does it work? Are community garden green roofs viable?

This is largely a question of operational planning, or what we might call the management and maintenance of the green roof. There are various important factors to consider in design, but aside from checking growing vegetables is viable in the conditions in the site and managing the high nutrient run off, the most important design considerations relate to the roof’s management and maintenance requirements.

Two key factors which determine whether or not a community garden succeeds on a green roof are its operating budget and the way in which the roof’s manager conceives his or her role.

In the community garden model, maintenance appears to be “outsourced” to the community. Property developers, design professionals and, above all, facility managers generally expect that a base level of maintenance will still be required. In fact, in my experience, the need for base level of maintenance by a facility manager is not inevitable. What is more or less invariable, however, is the need for more management.

It can be helpful to examine the real-life experiences of building communities which cultivate gardens on rooftops, such as the owner-occupant tended gardens of The Commons apartment building in Brunswick, Melbourne.

Rooftop vegetable gardening at The Commons

The Commons is an apartment building in the northern suburbs of Melbourne. Completed in 2013, it has 24 apartments over five floors. While it is not particularly large, it is spectacular in terms of sustainable design.

Its crowning jewel is a rooftop garden with sweeping views of Melbourne. The southern end of the rooftop is a green roof planted with hardy native species. It filters stormwater runoff from the building and acts as insulation for the apartments below.

At the northern end, the rooftop is dominated by raised garden beds. Residents can grow whatever they want in those plots, with vegetables and herbs an obvious choice. As such, The Commons is an exciting test of the potential for rooftop vegetable gardening in Melbourne.

My colleague, Paul Richards, visited The Commons in March to see how the plots have been doing. He spoke to Maryanne, an owner resident who has been there since the beginning, and learned the following:

The set-up

There are 46 plots for the residents to use for gardening. The plots have drainage systems underneath to collect water, and they are filled with a purpose-made soil.

Each one-bedroom apartment was allocated one plot, and every two-bedroom unit received two. Some of the spare and unused beds became communal.

There are no restrictions on what residents can grow. As a result, the roof has seen a wide range of edible plants such as rosemary, rocket, mint, tomato, lettuce, kale, spinach, cucumber, broad beans, and even a small olive tree. Plants like marigolds and geraniums have also been popular.

The residents are responsible for the maintenance of their beds. The beds are watered by hand, using rainwater (when available – the water supply switches to potable in drier times).  The residents have also created compost heaps and worm farms, to feed their plants.

The challenges

The first year was a resounding success.  Participation in rooftop gardening among the residents was high, and so were the rewards.

More recently, however, the rooftop has not been quite so bountiful. One of the biggest factors in the decline of the plots has been the weather. The beds are very exposed to the wind, and receive all-day sun with little or no shade. As a result, evapotranspiration is high, and the plots dry out quickly. Rainfall has also been in short supply, and the rare storms that occur have damaged the plants. The tomato plants have been particularly vulnerable to this storm damage.

The harsh rooftop conditions have also taken their toll on the soil. The soil used in the plots is quite fine to avoid clogging the drainage system, but this limits its capacity to hold water. The wind and sun can quickly remove what little water it stores. Despite the efforts of the residents in creating compost and using worm farms, it seems the soil also struggles to meet the nutrient needs of some of the plants. This particularly affects the edible plants, as these have higher nutrient and water requirements.

Under these conditions, and like most productive gardens, the beds need frequent attention to stay healthy. However, many residents have lapsed in their regular maintenance of the rooftop plots, and these plots are not actively cared for.

In addition to this exposure to the elements, the roof of The Commons faces a challenge from below. An issue with the roof membrane and its seal has resulted in some leaks. Though the issue is unrelated to the presence of the plots and other rooftop plants, it casts doubts over their future.

The future

There are many reasons to be optimistic about the future of rooftop vegetable gardening at The Commons, at least once the roof membrane is repaired.

Wind and sun protection are among the solutions under discussion; some wind breaks have already been installed, and appear to be working well. Placing small potted trees close to the gardens has also made a difference.

Wicking systems are another possible solution, provided the roof can accommodate the extra weight of the plots. This would go some way to improving the availability of water for the plants.

There are other opportunities for food production at The Commons, too. Some residents already keep edible plants on their wisteria-clad balconies, and there are productive beehives on the roof, where the bees enjoy their own version of communal, sustainable living.

As the history of the community garden on the roof of The Commons suggests, community garden green roofs require an operating budget which allocates resources to resolving issues as they arise. In this respect, community garden green roofs differ little from any other green roof (or garden, for that matter). Rarely, if ever, will all difficulties be known in advance.

What can be done in advance, allowing risk to be managed, is to allocate a budget for trouble shooting. Managing green roofs differs from the management of other green roofs simply in that a considerable portion of the trouble-shooting budget is likely to be spent on communication with and engagement of the community, whereas on some green roofs, the operating budget maybe largely allocated to horticultural maintenance.

With sound management, including clear communication to the community, the pioneering community garden on the roof of The Commons has proven its potential to continue to be both a viable and a valuable asset.

Co-authored by Shelley Meagher and Paul Richards of Do it on the Roof