Reed makes martinis with just-picked cola plant (Artemisia abrotanum), garnishes lamb with epazote (Dysphania ambrosioides) and adds Greek basil (Ocimum basilicum var. minimum) to her pickled and fried green tomatoes.

These plants and more are growing on the rooftop garden that Richard Thomas established - at the same time as Reed set up Mesa Verde - on top of the heritage-listed, art nouveau Curtin House. The herbs are fed with worm juice and castings and, in a nutrient-cycling loop, the worms themselves are on a diet of Mesa Verde organic waste and shredded menus.

Although Thomas had already proposed wicking beds and worm farms for the roof of the six-storey building when Reed decided to establish a restaurant on its top floor, the two planned the garden and restaurant in tandem.

Reed hates waste and has been obsessed with Mexican food for about a decade while Thomas is a nature-inspired installation artist who runs a worm-farm business. He wanted to create a "low-water, low-maintenance, nutrient-cycling garden in the middle of the city", while she wanted to establish a restaurant with an emphasis on the handmade.

Thomas said he saw the roof as a "great opportunity to do something incredible". But it was never going to be easy given the CBD building was close to 100 years old with heritage overlays, no crane access and insufficient weight-loading capacity for the sort of proposition Thomas had in mind.

A number of engineers said it couldn't be done. But then a "good engineer who took up the challenge" (paid by "visionary" building owners who were sympathetic to the roof garden idea) found it was possible to install a large steel frame atop the original roof with columns running down to the ground.

It took a couple of years to get the structure in place but Thomas was then free to fashion wicking beds from recycled timbers lined with old advertising banners. The beds are at waist height for easy picking and watered about once a week. The water is stored beneath the bed and gradually drawn up into the growing medium with capillary action. In heavy rain, overflow is collected in a tank downstairs. Thomas is now planning to introduce a pump to redirect harvested rainwater and wicking-bed overflow on to the roof so the beds become self-sufficient in terms of water.

He is still working to reduce the roof garden's exposure to sun and wind by training grape vines on trellis that curves over the top of some of the beds. While he used shade cloth this summer, ultimately he wants to rely purely on vegetation so visitors have the sensation of being surrounded in greenery. By arranging the beds into narrow corridors that you walk through (single-file) while surrounded by chillies, fennel, rocket, chamomile, eggplants and more, he has also played up the immersive qualities of the space.

But this relies on healthy plants and Thomas, director of Wormlovers, has used a growing medium of one-third worm castings, one-third perlite and one-third vermiculite with a scattering of rock dust (for minerals and trace elements). He says this mix keeps the weight down and the nutrients up.

A dilution of worm juice pepped up with a touch of molasses ("to kick the microbes along," says Thomas) is regularly applied to both the plant foliage and soil, while worm castings are dug into the soil when a new crop is planted.

The worms themselves - housed in five farms that Thomas imports from New Zealand - process about two kilograms of kitchen waste each day, with Reed having been able to do away with one of the restaurant's wheelie bins at a saving of $300 a month.

The plants are doing well on this regime and - aside from the sparrows that have taken to the sour Mexican gherkins and some of the radishes - are pest-free. Although the garden was never going to be able to put a serious dent in the Mesa Verde grocery bill (it mostly yields garnishes), Reed says that to "come up in the afternoon and pick things to use that night is a chef's dream: it doesn't get better".