Imagine sailing out to sea to tend to your garden underwater. Or envision a world where large scale farming could be moved into the depths of the ocean.

In a project dubbed Nemo's Garden, a team of engineers at Ocean Reef Group, a family-run scuba diving business, are currently experimenting with such ideas. They're trialling an alternative agricultural method which involves growing terrestrial crops in the sea. Now in their third year running, they think their underwater "biospheres"—soft plastic bubbles filled with air—could eventually provide the key to sustainably cultivating crops.

"My dad (Sergio Gamberini, president of the company) has a passion for gardening, and he thought that the sea—this enormous dispenser of thermal energy—would always give constant temperature, especially during the summers," Luca Gamberini, marketing manager of Nemo's Garden, told me.

"Sea temperature doesn't drop, whereas air temperature is a lot less stable as air molecules exchange heat very easily. We're studying how to harness thermal energy to benefit the growth of our plants."

While the sea is warmed up slowly by the Sun, it also loses heat less quickly, allowing temperatures to remain constant throughout the year.

Sergio Gamberini initially came up with the idea of growing plants underwater while holidaying with his family three years ago.

The team has so far taken seven transparent biospheres to depths of 7-9 metres beneath the Bay of Noli in Savona, Italy. Each air-filled biosphere consists of a hydroponics microenvironment, a structure containing the plants, and an anchoring system that attaches the mini greenhouse firmly to the sea bed. Hydroponics is a method of growing plants in mineral nutrients in water instead of soil.

"We want to be able to present the world with an alternative agricultural solution that doesn't require soil or [fresh] water."

"We wanted the concept to be simple so that any diver could assemble the biosphere underwater," Sergio Gamberini told me. He explained that when the balloon is taken underwater, it is inflated with air from a tank. As the pressure inside the biosphere is the same as outside it, no water enters the top part of the balloon. This means that when scuba divers tend to their plants, they can swim underneath the biosphere and enter the part of the biosphere filled with air—so while the lower half of their body is submerged in water, the upper half is in the water-free part of the biosphere where the plants are.

As the seawater evaporates, the water vapour condenses along the interior wall of the biosphere, creating a humid environment with a plentiful source of fresh water for the plants. The ocean environment also shields the plants from the parasites and abrupt changes in climate they would be exposed to on land.

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