Glass display cases in grocery stores are nothing unusual. But what is this one doing in the vegetable section of a Frankfurt supermarket? In fact, there is neither sausage nor cheese behind glass; instead, herbs stretch out into the purple artificial light. It is a small greenhouse. The customers look on with interest and skepticism. The lush green doesn't quite match the trays on which the plants are arranged in rows, as if in a laboratory. One shelf further on, the private label parsley finally makes its way into the shopping cart - origin: Germany, Morocco or Spain, may vary depending on the offer.

Spanish greenhouses are not exactly known for their economical use of water, fertilizers or pesticides. These glass showcases are quite different. They were developed specifically to allow crops to grow in them in a way that conserves resources as much as possible. This is because food production is increasingly reaching its limits worldwide: Arable land and drinking water are already scarce in many places, and climate change and its accompanying effects are likely to exacerbate the problem in many parts of the world in the future. Added to this is population growth. According to United Nations projections, some 9.7 billion people will inhabit the earth in 2050, around one-third of them in the metropolitan areas of large cities. More than two decades ago, Dickson Despommier of New York's Columbia University therefore began looking at ways of creating particularly economical greenhouses. This idea is also behind the glass showcases that the Berlin-based company Infarm is installing in supermarkets.

The saving starts with the space. Plants are stacked on top of each other on shelves in a very confined space - this new form of agriculture is called "vertical farming. If, in addition, sunlight is completely avoided in a completely enclosed space, this is known as "indoor farming. In principle, this can be implemented on any size scale: While agricultural entrepreneurs produce salads and herbs in industrial halls the size of a soccer field or set up glass showcases in supermarkets, hobby gardeners grow their greens in miniature farms that look like extravagant microwave ovens at first glance.

Vertical farming has long since moved beyond the experimental stage. The market research company Global Market Insights forecasts a growth rate of around 28 percent by 2026. Vertical farming is already being practiced on a large scale in America, Japan, Denmark and the Netherlands. One pioneer is the German company Infarm, which says it already produces salads and herbs indoors on an area of 50,000 square meters - mainly in supermarkets and restaurants. With central indoor systems in factory buildings, so-called growing centers, the company wants to increase this area tenfold within five years. Meanwhile, researchers and entrepreneurs around the world are working on indoor farming technologies.

"By growing crops vertically, we can produce more than a hundred times as much food on the same amount of land," says Simon Vogel, a biology lab technician working on indoor farming concepts at Fraunhofer IME in Aachen. The demand is considerable: food is now grown on half the land in Germany, and yet around 65 percent of vegetables in this country are imported. "With the help of indoor farms, less food needs to be imported," Vogel says. Space-saving greenhouses even fit into urban centers. Herbs and salads then grow where they are consumed, reducing the need for transport and therefore CO2 emissions.

Photo by Satish Kumar on Unsplash