NASA's big foray into plant growth is an experiment called
Veggie (Vegetable Production System), which is intended to provide edible food for the astronauts. The first type of crop it grew was lettuce, to great success. After a precursor crop was sent to Earth to look for any potential problems, astronauts were able to munch on the harvest in space a few months later.
The follow-up zinnia growth, however, proved more troublesome. NASA controllers saw mold on the flowers around the holiday season in December 2015, and had difficulty relaying up timely instructions to care for them. Astronaut Scott Kelly then, with permission from the ground, took on full responsibility for saving the plants. While some died from the mold,
zinnias successfully bloomed in space in January 2016.
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While Veggie is one of the newer experiments on station, its advantage is sheer size: according to NASA, it has the largest volume available to grow plants on the orbiting complex. In other words, bigger plants can grow up in space. The bonus for astronauts, NASA stated, is they can have a "tool for relaxation and recreation" in between their experiments.
Image: A zinnia flower blooms on the International Space Station in January 2016, weeks after mold was found in the experiment and removed (NASA)