“A field can be the least efficient place to grow food,” Mike Zelkind told the Globe and Mail. “An indoor farm can produce more than 300 times more food, with 100-per-cent renewable energy and 97 per cent less water. That’s the beauty of growing in buildings.”

And so Montreal’s Lufa Farms has now built, in the heart of Ville Saint-Laurent, what is being called “the world’s largest rooftop greenhouse.

The new greenhouse spans 160,000 square feet (15,000 square meters), or about the size of three football fields.

“When we started [in 2009], we considered leasing parking lots for growing, but no one wanted to give them up,” Mohamed Hage, Lufa Farms’ CEO, told the Globe and Mail. “But for most commercial building owners, rooftops are unloved – they leak, they have to be maintained and, in a cold climate like ours, you have to clean off the snow. A commercial rooftop greenhouse is a solution.”

Another variable playing a role in Lufa’s decision to invest in the new greenhouse was Covid-19.

“In March, 2020, we saw a doubling of demand for our food. Growing food locally on rooftops and sourcing from local farming families allows us to swiftly adjust and respond to this demand,” Hage told the Globe and Mail.

Mr. Hage points out that a rooftop greenhouse also makes great sense in terms of environmental sustainability and reducing energy and carbon emissions.

“We don’t use pesticides and our greenhouses use half the energy that a greenhouse at ground level would consume because we use heating from the building that rises up to the roof,” he told the newspaper.

Ten years ago Lufa Farms spent $2.2 million on its first greenhouse, a ground floor one. The new mega greenhouse - the company’s fourth - costs more than a ground level alternative, but the company didn’t reveal its price tag.

According to Phys Org, the concept of rooftop greenhouse is gaining traction. American Gotham Greens constructed eight greenhouses on roofs in New York, Chicago and Denver, and French Urban Nature, and is planning one in Paris in 2022.

At Lufa, about 100 varieties of vegetables and herbs are grown year-round in hydroponic containers lined with coconut coir. Produce like lettuce, cucumbers, zucchini, bok choy, celery and sprouts grow in the containers.

Bumblebees pollinate the plants, while wasps and ladybugs keep aphids in check, without the need for pesticides.

Lufa’s vegetable haul each week can feed 20,000 families, with baskets tailored for each at a base price of $30.

A huge distribution center on the ground floor of the new greenhouse brings together nearly 2,000 grocery products for offer to customers and restaurants.