The tomatoes aren’t cooperating. Instead of growing up the trellis, the plants are weaving all over the garden bed and arching, menacingly, toward a young grapevine. On a hot August afternoon, Pauline Benetti and Diane Kelsey are trying to coach the fruit upward by tying its stems to the wood-and-metal trellis.

It’s high season for the juicy red spheres, but these two volunteers – both shorter than the vines they’re trying to wrangle – aren’t just struggling with these plants for the final farmers’ markets of the summer. They want to train the tomatoes to grow in the right direction inside this greenhouse all year long.

Their work is part of a five-year effort by the Geothermal Greenhouse Partnership (GGP) in Pagosa Springs, Colorado. The volunteer-run nonprofit, in coordination with the south-west Colorado town, is transforming the world's deepest geothermal hot spring into something much more than just a travel destination: it’s using the renewable energy source to grow food year-round for the community.

Pagosa Springs is well-known in the western United States for its unique approach to geothermal energy, which is energy harnessed from the Earth’s heat. Geothermal food growing, though, is a new enterprise.

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In the centre of the small downtown, on the banks of the San Juan River, sit three conspicuous, geodesic greenhouses, each 42ft (13m) in diameter. They stand in stark contrast to the old-timey buildings on the road above. All will house gardens, but each has a different mission.