Astronaut scott kelly tweets a photo of a zinnia flower grown in space

It's not the first time plants have sprouted in space.

The ISS team installed the space station's Veggie plant system in mid-2014 and have also grown "Outredgeous" red romaine lettuce.

The vegetable was grown aeroponically -- that is, in an air or mist environment without soil. Plants grown aeroponically require far less water and fertilizer, don't need pesticide, are much less prone to disease, and grow up to three times faster than plants grown in soil, NASA has said.

In a blog,NASA wrote that this was the "first time a flowering crop experiment will be grown on the orbiting laboratory".

NASA was not immediately available for comment.

But some have argued that a sunflower was actually the first flower to grow in space.

In 2012, astronaut Don Pettit successfully grew a zucchini,sunflower and broccoli out of zip-lock plastic bags on the ISS as personal science experiment. Pettit documented the life of his "companions" in a NASA blog called "Diary of Space zucchini"

Still, these small victories are just the beginning.

"I hope to see Veggie's success as the first step in food production that will allow astronauts on the space station to enjoy fresh food and gain knowledge as we explore beyond low-Earth orbit," saidBrian Onate, who helped build the plant growth system before it went into space.

The Veggie project will also produce crucial information for a Mars mission, said Alexandra Whitmire from NASA's Human Research Program. For example, understanding watering schedules in microgravity, and knowing what to do if there is mold growth or other challenges in these extreme conditions.

"In future missions, the importance of plants will likely increase, given the crews' limited connection to Earth," Whitmire wrote in a NASA blog.

She added that growing plants in space also has psychological benefits for astronauts, particularly in combating feelings of isolation and loneliness.

"Plants can indeed enhance long duration missions in isolated, confined and extreme environments -- environments that are artificial and deprived of nature," she said. "While not all crew members may enjoy taking care of plants, for many, having this option is beneficial.

"Studies from other isolated and confined environments, such as Antarctic stations, demonstrate the importance of plants in confinement, and how much more salient fresh food becomes psychologically, when there is little stimuli around."

NASA hopes Veggie will become a regular facility for ISS astronauts to grow fresh food in space.