Plants in Space: Growing Lettuce and Flowers on the ISS

If people are to live on the Moon and travel to Mars, they will have to grow food in space. That is why plant experiments have been running on the International Space Station for more than a decade, from lettuce to flowering zinnias. Here is how plants grow in microgravity and what has been achieved.

Down-to-earth plants for your home: potted plants.

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How plants grow without gravity

On Earth roots grow down and shoots grow up because of gravity. In microgravity plants orient mainly towards light, so the lamps are placed above them. Water does not drain downwards but forms blobs that can either dry the roots out or starve them of air, so plants are grown in special substrate “pillows” with a controlled water supply.

The Veggie unit and the first lettuce

In 2014 NASA’s Veggie unit, a small chamber with LED lights, began operating on the ISS. The red and blue LEDs make the plants look pinkish. In August 2015 astronauts tasted station-grown red romaine lettuce for the first time; part of the harvest was frozen and returned to Earth for analysis. Cabbage, mustard greens, radishes and chilli peppers followed.

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The first flowers in space

Flowers are harder to grow than lettuce: they take longer and need more precise conditions. In early 2016 zinnias bloomed on the ISS. The experiment nearly failed as the plants suffered from excess moisture and mould, and an astronaut had to adjust the watering by eye, like a gardener. The experience helped scientists work out how to automate plant care on future missions.

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Why it matters

• Fresh food. On long missions vitamins in stored food break down, and fresh vegetables add variety to the diet.
• Closed life support. Plants absorb carbon dioxide, release oxygen and help purify water.
• Wellbeing. Astronauts report that tending plants and seeing greenery helps them cope with isolation.
• Science. Experiments show how gravity shapes growth and help breed hardier crops for Earth.

Plants on the Moon

In 2019 China’s Chang’e 4 lander carried a small biosphere to the far side of the Moon, where cotton seeds sprouted: the first shoot on the Moon, although the experiment was short-lived.

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Plants help us on Earth too, though, contrary to a popular myth, a few pots will hardly clean the air in a flat noticeably. More in “Do houseplants purify the air?”, and for more surprising plant facts see “Interesting facts about flowers”.

FAQ

Why do plants on the ISS look pink?

They are lit by red and blue LEDs, the parts of the spectrum plants use most for photosynthesis.

Could we grow plants on Mars?

Scientists are studying it, but Martian soil contains harmful salts, so plants would need greenhouses and prepared growing media.

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Author: Maria Svitlovir

Graduated from Taras Shevchenko National University of Kyiv, Institute of Biology and Medicine (2001). BSc in Biology, MSc in Horticulture. Writes about plants, works at a garden centre selecting and repotting plants, and contributes to plant reference guides.