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Pak Choi At 1.1km: Inside The World's Deepest Farm

Aug 24
3 min read

More than 1,000 metres beneath the North Yorkshire coast, in a science facility better known for hunting dark matter, researchers are cutting pak choi and lettuce from vertical growing towers.



The world's deepest underground farm has been established at Boulby mine near Saltburn, a working operation run by ICL-UK and the world's only commercial producer of polyhalite, the fertiliser. The farm is a partnership between the University of Sheffield and Farm Urban, and its purpose is evidential: to establish whether uniform, marketable crops can be grown underground at commercial standard.


The team believes disused mines could offer the stable environment and existing infrastructure needed to cut the punishing energy costs that have dogged conventional vertical farming. What they need now is proof — and they do not think they have long.


"The crisis is less looming, it's here"


"We need to double food production by 2050 to support the world's population," said Jacob Nickles, a University of Sheffield research fellow and one of the project's leaders. "That is the long and the short of it. Is it possible? Maybe if we start using mines."


This year has sharpened the argument. England's hot, dry summer has killed crops and forced livestock farmers onto winter feed for want of grass. "The crisis is less looming," Nickles said. "It's here … now."


He is careful about the claim being made. "We're not here to replace conventional farming. We're here to work alongside it, and there are some things that are just uniquely better suited to controlled environment agriculture. Lettuce is a really good example."


Getting to work


Reaching the crop is not a matter of walking into a glasshouse. Access requires two detailed health and safety inductions, a change into hi-vis, and an eight-minute descent in the mine's original lift, built more than 50 years ago.


At the bottom it is noticeably warm, and remarkably shielded. "You're experiencing a million times less radiation than you were 10 minutes ago," the laboratory's engagement officer, Jonny Gutteridge, told visitors. "Does it feel nice?"


Growing happens in the salty tunnels and in air-conditioned laboratory space. The kettle boils hotter than it would at the surface; the site also has the UK's deepest flushing toilet.


The commercial arithmetic


Climate control is the cost that has repeatedly sunk controlled environment agriculture, and it scales with every square metre of growing space. Deep rock holds a stable temperature year-round, with no seasons, no weather and no outdoor pest or disease pressure to design around.


The Boulby team is targeting a 30–50% reduction in operating expenditure by stripping out HVAC and biosecurity costs, and is testing that through techno-economic analysis, cost-benefit analysis, life cycle assessment and multi-criteria decision analysis. Growing units had to be built as modular systems sized for the lift shaft; the hardest engineering problem proved to be levelling on a floor that shifts over time.


Staff need mine safety training and, once underground, are there for most of the day, so daily oversight falls to resident technicians backed by remote sensor monitoring.


The backdrop is a tightening supply picture: UK self-sufficiency in fresh vegetables stood at 53% on 2023 Defra figures, the lowest since records began in 1988.


The cautionary example is close to hand. Growing Underground, which grew salad 33m below Clapham in a wartime air raid shelter, was Britain's best-known subterranean grower; its operating company, Zero Carbon Farms Ltd, is now in liquidation, according to Companies House.


Cheaper climate control solves one input cost. It does not by itself fix the category's economics — which is exactly what Boulby's trials are designed to test.



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