A butterfly perching on a lettuce leaf is not normally a cause for marvel. But I am standing on the roof the Bank of America Tower, a 39-floor building in the heart of Hong Kong’s busiest district, to see one of its highest farms. The butterfly must have flown across miles of tower blocks to reach this small oasis amidst the concrete desert.

“You just plant it out and nature comes and enjoys it,” says Andrew Tsui. We are joined by Michelle Hong and Pol Fabrega, who together lead Rooftop Republic, a social enterprise that aims to turn the city’s dizzying skyline green.

If it weren’t for the fact that we are 146 metres (482ft) above street-level, this farm would look like any allotment site or garden courtyard – row after row of rectangular crates, some with fresh sprouts poking through the surface, others with established plants almost ready for harvest. The loudest noise I can hear is not the traffic below, but the wind.

Although it is only February when I visit, the sun is so strong I end the morning with a slight tan, and Hong tells me that the local climate offers ideal growing conditions for most of the year, meaning that despite the exposure, they can cultivate a range of plants. “We have things like cherry tomatoes, salad, broccoli – all of that can be grown here,” explains Hong. The greens I see today are as lush as anything you would find growing at sea level. Workers from the offices below tend it day-to-day, and after harvest, the fruits of their labour are sent to a food bank, where they fill lunchboxes for the needy. “We want to share the good products – not just the leftovers,” says Tsui. On other projects, however, the farmers would take the produce for themselves.