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The two Chinese astronauts, Jin Haipeng and Chen Dong, have successfully grown some vegetables in the weightless lab.

Lettuce grows in the Tiangong-2 space lab. [Photo provided by Astronaut Center of China]

Jing Haipeng introduced how to grow them via video on Friday, the 24th day after they entered Tiangong-2. They planted the lettuce late October in a 3D-printed cultivation box filled with vermiculite. Unlike growing plants on earth, astronauts must water the vermiculite first before putting seeds in.

There is also at least 14 hours long of lighting provided daily for the sake of photosynthesis. Astronauts have also injected air into the roots of the plants. They measure the moisture and nutrition content, photograph, water and thin out the seedlings at certain times every day.

But the astronauts can not eat their lettuce in space this time. They will take samples of the lettuce back to the earth next week.

Wang Jilong, a researcher under the space center, said: "We would like the lettuce can be eaten in the future. But this time we would at first examine its bio-security. We hope the next time, the astronauts can have some of this vegetable in space."