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How to Start Your Own Edible Rooftop Garden

By Bianca Husodo

 
Tung Pham
 

In a hilly estate in Ang Mo Kio, where Singapore’s skyscrapers are hardly within one’s visual periphery, is a stretch of identical residential four-story buildings, each structure a mirrored simulacra of the other next to it. On the topmost story of one of these houses, however, is the sprouting mini forest-like outline of a lush rooftop — a stark contrast to the near-uniform, teak-floored outdoor terrace replete with a canopy and barbeque pit.

Joanna Chuah runs the private edible rooftop garden on top of her family house. The 24-year-old lawyer-in-training has been practising her green thumb for a decade, but she only began cultivating her rooftop garden three years ago, devoting it as her “experimental zone”, where she archives her collection of rare plants. She documents them too on a dedicated Instagram account, Weird & Wonderful Edibles (@wwedibles.sg), often captioning the posts with informative gardening musings. She holds sporadic workshops at her other garden in Bukit Timah — the first garden she grew up tending to — educating those who would like to learn more about medicinal herbs and edible plants.

Her rooftop garden is not the classic green roof that requires substrates of soil as its foundation: Chuah does container gardening. The space, blanketed with grass carpet, is brimming with little elevated plots and pots — lined on the ground or stacked on shelves. The bustling clusters of herbs, flowers, fruit trees and vegetables make for a shambolic beauty.

Tung PhamContainer gardening requires tactical plotting the groups of your plants; be it to shade a less hardy plant, symbiotically complement each other in nutrition on the same plot, or prevent pests.
Container gardening requires tactical plotting the groups of your plants; be it to shade a less hardy plant, symbiotically complement each other in nutrition on the same plot, or prevent pests.
Tung PhamJoanna Chuah, 24, a horticulturalist and city gardener, who maintains her own edible garden on the roof of her family house in Ang Mo Kio.
Joanna Chuah, 24, a horticulturalist and city gardener, who maintains her own edible garden on the roof of her family house in Ang Mo Kio.

Around the world, a renewed shift towards urban gardening has taken place. Perhaps driven by a yearning to detach from the digital sphere, plant-loving millennials are spearheading the movement. And in Singapore, while urban farms and communal rooftop gardens have been part of a government scheme for a decade — sprawling beds of vegetables and greeneries are staples on modern high-rise buildings — nurtured gardens with a wide variety of plants are hard to come by in residential areas. Spatial restriction being the main reason.

Well, it shouldn’t be.

To Chuah, it’s like having her own small oasis at home. Within the confines of the six by 12-metre patch (“It’s not large. This space is very condensed,” Chuah remarks), the self-taught horticulturalist collects more than 100 types of plants — a large part of them are oft-times forgotten native tropical plants, from green-petalled heritage roses (a type from a pre-insect period before it evolved to have colours) to Brazilian tea trees (which produce mushroom-tasting flowers) — that Chuah sourced from fellow collectors or private gardens.

“It was interesting to start a movement. At that point in time, people weren’t using edible flowers,” Chuah says of the start of her interest in lesser-known varieties that has led curious Singapore-based chefs and cooks to order small batches from her harvest. “So I thought, that’s a creation of value. If you just have something that has been around for a long time and you’re just trying to mimic that, then to me, it’s boring.”

Tung PhamChuah pruning and picking herbs from the garden.
Chuah pruning and picking herbs from the garden.
Bianca HusodoThe harvest from an edible garden can be easily used for homemade drinks and dishes. Here, Chuah’s  iced tea that’s brewed from passionfruit marigolds and Japanese menthol mints.
The harvest from an edible garden can be easily used for homemade drinks and dishes. Here, Chuah’s iced tea that’s brewed from passionfruit marigolds and Japanese menthol mints.

The upside of gardening on your roof is well documented. Green roofs not only retain rainwater, decreasing sewer discharge, but they also cool down the house’s temperature while also helping reduce air pollution. With height in your favour, it will be less accessible for pests to plague the garden. Even if they do, container gardening — where everything is done in movable pots — allows easier isolation for infected plants, rather than having to uproot them out of the ground, risking their death.

Of course, gardening on a concrete surface has its own set of setbacks. For one, proliferating living organisms on a roof may impact its real estate value. “You can imagine if you put all these on the carpet grass, it’s going to be a huge hassle if you plan on selling the house,” Chuah elaborates. “You’ll have to move all of the plants down, find buyers for them and then get rid of the soil stains.”

Here, we talk to Chuah to find out what it takes to plant and maintain a variegated verdant roof.

Do Your Research

“You might want to go out and get physical contact with the farms and the gardens,” advises Chuah. She suggests scheduling a visit to local farms — the likes of Pacific Agro Farm, GreenCircle Eco-Farm, vertical farm ComCrop — to tour and buy the plants you’d like to grow on your roof. If you’re looking to grow lesser-known varieties that will suit the equatorial climate, read up. “Sometimes I would go to the horticultural library at Singapore Botanical Gardens. It’s a plant library. They have interesting documents that tell you about different kinds of plants that you can grow for medicinal purposes. Another very good resource will be the reference library on the eleventh level of the National Library and the national archives.”

Tung PhamGreen-petalled heritage roses, a variety originating from a pre-insect period before it evolved to have colours.
Green-petalled heritage roses, a variety originating from a pre-insect period before it evolved to have colours.
Tung PhamAquatic plants — pictured here are Chuah’s water hyacinths and water lilies — can be fertilised with tilapia fishes, which can co-live in the same pond and obliterate the outbreak of mosquitoes.
Aquatic plants — pictured here are Chuah’s water hyacinths and water lilies — can be fertilised with tilapia fishes, which can co-live in the same pond and obliterate the outbreak of mosquitoes.

Start with Hardy Plants Before Finicky, Rare Types

“I would suggest starting with local vegetables. Like Brazilian spinach, for example, it’s so easy to grow. You can grow them by cuttings and put them in soil. They’ll grow in any kind of soil,” says Chuah. As you progress, you can go on to flowering plants and local herbs, like ulam raja and butterfly pea.

Be Smart With the Space You Have 

Plan ample paths around the plants — enough to fit a pruning squat — for you to care for them. “The way we did it is like a maze. We try to increase the surface area of the space by creating small walkways and allowing the plants to line them,” explains Chuah. Save up more space by stacking them on a shelf.

Get to Know Your Plants

Some plants require elevation from the ground, as the concrete floor may be too hot for them during the day. Take down notes of their progress in a journal to see what works, what doesn’t, what they need. And planting in pots as opposed to the ground’s soil limits the nutrient diversity a plant derives — hence companion planting is necessary. She doesn’t randomly group her plants. Her ulam raja, for instance, is grown together with peanuts as they absorb the nitrogen that the ulam raja needs, and both their growth cycles are similar. Her Mrs. Burns lemon basils, a heritage basil that Chuah specifically bred, are paired with marigolds so that they have shade and the soil is protected. Chuah concludes, “It’s putting the right things at the right place.”

Tung PhamLabelling the names of the plants helps in journalling their quirks and preferences.
Labelling the names of the plants helps in journalling their quirks and preferences.
Tung PhamThe gardening tool corner.
The gardening tool corner.

Try Fertilising and Fighting Pests Organically

Sharing the pond with Chuah’s aquatic plants are tilapia fishes. “They provide fertiliser for the plants, eating all the mosquitos and keeping all the small fishes in check so they actually eat the guppies when they overpopulate,” she explains. Marigolds are great, too, to battle nematodes (little worms that gnaw on roots). Chuah also makes her own fish emulsion to ferment them into DIY fertiliser. “They’re basically dead fishes. I put them in a big pail, put some sugar, water and I pump in oxygen. The good bacteria then grows.” Sometimes, Chuah buys chicken ordure too. “It’s, like, S$1. It’s chicken poo.”

Be Prepared to Clock in Hours of Garden Work

Chuah spends seven to eight hours a week tending to her garden, usually backlogging them during the weekends. She checks on, prunes and waters her plants (she uses a Vegepod, a nifty self-watering raised bed that collects rainwater, for some of her herbs). She would spend time making her fertiliser. “There’s a lot of hard work and dedication maintaining this. Nothing looks like this just naturally. In the wild, plants don’t look as perfect as that. They have spots, fungus infections. Here, the plants look nice, and that requires a lot of effort.”

Experiment With Your Edible Harvest

Chuah usually whips up a motley of leaves, herbs and flowers into a salad for her family and herself to enjoy; the flowers can be peppered as garnishes; certain types of herbs have medicinal purposes. Sometimes, she’ll brew them into a refreshing beverage. One of her favourites is a mint tea, made from a mix of passionfruit marigolds and Japanese menthol mints. “You can just let them sit in hot water for a while, and then throw in some ice,” she says.