Zinnias have bloomed on the International Space Station, the first fully grown by NASA in space. 

U.S. astronaut Scott Kelly tweeted photos of his orange success over the weekend, wowing millions of people down here on Earth with shots of a zero gravity salad-worthy zinnia from the space station's Veggie lab. 

The plants almost never made it to maturity though, as the zinnias were covered in mould back in late December. 

Two weeks after planting a batch of zinnias, Kjell Lindgren, another NASA astronaut, saw that water was leaking out of the leaves, according to NASA. There were multiple signs that the plants appeared to be drowning. 

"When you have high humidity and wet surfaces leaves start dying, and become prime real estate for mould to grow," Trent Smith, the Veggie project manager, told NASA in a release published Saturday.

Lindgren handed off gardening duties to Kelly when he returned to Earth on Dec. 18, but once Kelly arrived, the zinnias had twisted leaves and were already partially dead. Mould began to spread on the plants. 

Kelly sliced off the mouldy tissue, sanitized the remainder, and then tried to dry out the zinnias with fans. Those mouldy pieces were then stored away for further study on Earth. 

The fans, however, then caused the plants to become too dry. 

On Christmas Eve, Kelly told the ground support team that they needed to be watered, but there was nothing in the watering schedule until Dec. 27. So, Kelly asked if he could just water them himself. 

NASA later referred to him as "an autonomous gardener aboard the space station."

Two of the plants died, but two zinnias — likely destined for further study (or a later lunch) — survived. 

The whole space gardening enterprise is designed to help scientists study how plants react to being grown off Earth, and to prepare astronauts for a future trip to Mars. 

The prospect of a Mars trip was one reason Kelly felt justified in taking over the plants' care (and why he made a reference to The Martian's Mark Watney).

"You know, I think if we're going to Mars, and we were growing stuff, we would be responsible for deciding when the stuff needed water," he said to the ground team, according to NASA. "Kind of like in my backyard, I look at it and say 'Oh, maybe I should water the grass today.' I think this is how this should be handled."

These are not the first plants NASA has grown on the space station, or even the first flowers to bloom in space — but they are NASA's first flower that has grown entirely, from seed to maturity, in space.  

In 1982, Russian cosmonauts managed to grow rock cress on the Salyut-7 satellite, according to the Guinness World Records.

The last time NASA tried to grow plants in space, astronauts raised some red romaine lettuce. That's after they accidentally drowned some, however, showing that in some ways, astronauts are just like the rest of us: They occasionally over-water or dry out their plants. 

But unlike the rest of us, they get to taste the fruits of their labour while in orbit.