In the movie The Martian, the hero Mark Watney is an astronaut struggling to stay alive on Mars. In order to survive, he grows potatoes in the Martian soil. Could it really be possible to grow plants in space on Mars or on the moon? The answer is partly no, because we have not had the opportunity to try growing any plants on Mars or on the moon. But the answer is also yes, because we have been growing plants in space in the confined environments of various spacecraft for several years. In the movie The Martian, astronaut Mark Watney employs some innovative methods to cultivate potatoes on Mars.

The ISS orbiting around Earth serves as a space laboratory where crew members live and conduct research.↵
In the early days of space travel, plants were grown on spacecraft primarily for research purposes — to better understand how they functioned and how they grew under different conditions, such as in microgravity and closed environments. In recent years, however, NASA has seriously started investigating the potential of space-grown plants as a food source for astronauts. Fresh food provides valuable nutrients as well as variety, unlike the dried and packaged food that makes up most of an astronaut's diet. Therefore, finding a way to continually supply astronauts with fresh food has long been a desire for NASA.

In addition to health benefits, a bit of space gardening can also offer psychological benefits for astronauts. Observing and caring for plants can relieve their stress and improve their moods. Plants are a living, growing piece of Earth; therefore, their smell and color can inject a bit of sensory variety into an artificial lifeless environment. With the sun rising and setting as many as sixteen times a day on the ISS, astronauts suffer from sleep disorders. Space gardening can minimize this problem by helping astronauts mark the passing of time.

While it is not yet happening on a large scale, plants grown on a spacecraft may be used to potentially reduce carbon dioxide and produce oxygen, as well as provide water for drinking through transpiration. In this way, growing plants in space may help to provide a more habitable environment for humans.↵
Still, there are questions that need to be answered. First, what essentials are needed for plants to be able to grow, and second, in what ways can these essentials be provided on a spacecraft?↵
Plants must have water, soil, gravity, and light, all of which are in short supply on a spacecraft. Experiments over the years have been slowly but surely developing ways of growing plants in space with very little of these essential requirements.

Water is especially scarce on the ISS, and the amount used is controlled and recycled as much as possible. About 93 percent of all water on the ISS is reclaimed from the collected breath, sweat, and even urine of the ISS inhabitants. It's a similar story with soil. A spacecraft is not going to be able to carry around masses of heavy, dirty stuff that can be used to grow plants. In addition, soil and water tend to float away because of the lack of gravity.

For these reasons, NASA has developed a special container called a Veggie, which is specifically designed for space-gardening on the ISS. The Veggie creates a suitable artificial environment for plants to grow and flourish under conditions of weightlessness. It contains plant pillows and a reservoir. Plant pillows are bags of dirt, fertilizer, and nutrients. Small wicks that seeds are glued onto are inserted into the bags to soak up the water. A reservoir of water is at the Veggie's base, and it is covered with a fabric that allows the water to pass through it. A similar fabric on the bottom side of the plant pillow allows the water to soak into the soil.

What about gravity? On Earth, gravity has been thought to be necessary for roots to grow in the right direction — down and away from the leaves. In a weightless environment, there is no up or down, so roots grow in all directions. Research done in 2010 on the ISS, however, showed that gravity is not an important factor for plant growth. This research proved that plants do not need gravity in order to grow normal root patterns and send their leaves upward toward the light. Plants grow more slowly, but as long as they have a light source above them, they are able to grow in the right direction. The light source, however, needs to be sufficiently strong and directed.

This intense light source is indispensable for photosynthesis.* On Earth, most plants get this light from an obvious, abundant source, the sun. But in a spacecraft, the sun's solar radiation is usually not best for plant growth because the position of the vehicle is constantly changing. Thus, NASA has adopted LEDs for the light source. LEDs use less energy and last longer than old-fashioned lights. LEDs emit little heat, so moving them closer to the plants won't cause the plants to dry out or be burned.

Knowing how to grow plants in confined spaces is not just of benefit to salad-hungry astronauts. Experiments with plant production on the ISS have also proven valuable for agriculture on Earth, especially for areas in which water is scarce, soil is poor, or space is limited. For example, vertical farming with an electric light source is now widely used in many countries. Continued experiments in space gardening will give more insight into how plants can be grown successfully in challenging environments. Space gardening is good not only for astronauts in space but also for people on Earth, helping to solve the problems of how to face a changing climate and a growing world population.