In some cities, as many as one in four office spaces are vacant. Some start-ups are giving them a second life – as indoor farms growing crops as varied as kale, cucumber and herbs.

Since its 1967 construction, Canada's "Calgary Tower", a 190m (623ft) concrete-and-steel observation tower in the capital of Alberta, has been home to an observation deck, panoramic restaurants and souvenir shops. Last year, it welcomed a different kind of business: a fully functioning indoor farm.

Sprawling across 6,000 square meters (65,00 sq ft), the farm, which produces dozens of crops including strawberries, kale and cucumber, is a striking example of the search for city-grown food. But it's hardly alone. From Japan to Singapore to Dubai, vertical indoor farms – where crops can be grown in climate-controlled environments with hydroponics, aquaponics or aeroponics techniques – have been popping up around the world.

While indoor farming had been on the rise for years, a watershed moment came during the Covid-19 pandemic, when disruptions to the food supply chain underscored the need for local solutions. In 2021, $6bn (£4.8bn) in vertical farming deals were registered globally – the peak year for vertical farming investment. As the global economy entered its post-pandemic phase, some high-profile startups like Fifth Season went out of business, and others including Planted Detroit and AeroFarms running into a period of financial difficulty. Some commentators questioned whether a "vertical farming bubble" had popped.

But a new, post-pandemic trend may give the sector a boost. In countries including Canada and Australia, landlords are struggling to fill vacant office spaces as companies embrace remote and hybrid work. In the US, the office vacancy rate is more than 20%.

"Vertical farms may prove to be a cost-effective way to fill in vacant office buildings," says Warren Seay, Jr, a real estate finance partner in the Washington DC........

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