The challenge of feeding a planet that’s set to have 3 billion more people on it by 2050 - made even more acute by climate change as some parts of the planet become wetter, while others drier - means the pressure is on to find ways to feed the planet. So farming has to become more productive – and new areas to grow, especially in dry climates, must be found. One potential solution: hydroponics.

Farming with little space and producing higher crop yields: hydroponics fits the bill. Though it may sound like something out of Star Trek, it's actually been around since the Aztecs – they built floating farms around the city of Tenochtitlan. Hydroponics essentially means growing plants without soil, and instead using a nutrient-rich solution to supply them with water and minerals.

With hydroponics, plants – usually supported by soil – are propped up artificially instead, and a nutrient solution is applied to the suspended roots using a number of different methods, including spraying them with a solution mist. Together with artificial lights, heaters and other equipment, the nutrient solutions help plants develop faster, produce larger yields and grow all year round.

Hydroponics can recycle water, meaning it could use as little as 10 percent of the water a conventional farm uses – making it an option in arid environments. And the closed system means nutrients don't escape, cutting fertilizer down to as much as a quarter of what a conventional farm would use. Also, almost no pesticide is needed, since soil pests aren't an issue for plants grown without soil.

When growing sideways isn't an option, try going upwards: hydroponic growing trays can be piled on top of one another, and plants can be grown more closely next to each than in the soil, making it very efficient in terms of space. As for what kind of space they can grow in, the sky is the limit: with no need for scarce farmland, one possibility could be to have hydroponic farms in skyscrapers.

Running a hydroponic farm can be complex, energy-intensive and expensive. Plants require many essential nutrients, and the farm needs a large amount of equipment. Heat and light, supplied for free by the sun in conventional farms, have to be provided artifically and paid for. And power failures could mean whole crops are destroyed if they go too long without water and light.

Hydroponics can theoretically be used to grow any crop, although the technique lends itself best to plants such as cucumbers, salad greens, tomatoes, peppers and herbs. Given its long history, hydroponics still isn't widely used. But that looks set to change: the global hydroponic farming industry was estimated to be worth $21.2 billion in 2016. That's forecast to grow by 7 per cent each year.