The crew aboard the International Space Station has exercised their green thumbs to grow the first flower ever to bloom in space, a brightly colored zinnia that blossomed in the orbiting lab's zero gravity vegetable garden.

Designated ISS gardener Scott Kelly shared images of the zinnia, chosen by NASA for its hydroponic Veggie lab to help understand how plants can grow and flower in microgravity.

ISS crew members had previously grown red romaine lettuce in 2015 and even enjoyed it as part of a meal, but scientists were interested in how flowering plants could be grown in space.

"The zinnia plant is very different from lettuce," says Veggie project manager Trent Smith, citing its sensitivity to environmental and lighting parameters and its longer growth period of 60 to 80 days. "Thus, it is a more difficult plant to grow, and allowing it to flower, along with the longer growth duration, makes it a good precursor to a tomato plant," he says.

There are plans to grow tomatoes on the space station in 2018, while Chinese cabbage will join the zinnias in the orbiting garden later this year.

Zinnias are edible and are often featured in salads. The astronauts say the space-grown zinnias look similar to those grown on Earth with the exception of a curled edge on the petals, probably a result of the microgravity environment.

Edible produce grown aboard a spacecraft would be a vital food source on long space missions such as NASA's proposed journey to Mars, scientists point out, and would be an important supplement to astronauts' diets, which normally are mostly food that has been freeze-dried for long storage.

"The farther and longer humans go away from Earth, the greater the need to be able to grow plants for food, atmosphere recycling and psychological benefits," says Dr. Gioia Massa, Veggie science team leader for NASA. "I think that plant systems will become important components of any long-duration exploration scenario."

The Veggie plant growth system has been on the Space Station since April 2014. LED lights illuminate the plants growing in the system, with fertilizer being automatically released at set intervals.

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