There are significant challenges to growing vegetables in space. Without gravity, plants rely on other signals to know which direction to grow, like the presence of light and water. NASA project manager Trent Smith, who's part of the team that designed Veggie, explained how ISS's plant-growth system works to the Daily Dot: "[T]he LED lights in Veggie signal the shoots to grow towards the light and roots towards the water and darkness of the plant pillows. ... Roots need both water and air at the same time, and getting that mix right is extremely challenging."