It’s not easy having a green thumb in space. Without gravity, seeds can float away. Water doesn’t pour, but globs up and may drown the roots. And artificial lights and fans must be rigged just right to replicate the sun and wind.

But NASA has decided that gardening in space will be crucial for the next generation of explorers, who need to feed themselves on missions to the Moon or Mars that may last months or years.

Necessary nutrients, like vitamins C and K, break down over time in
freeze-dried foods. Without them, astronauts are increasingly vulnerable to infections, poor blood clotting, cancer and heart disease.

So the US space agency has turned to professional botanists and novice gardeners -- high school students, in fact -- to help them practice.

“There are tens of thousands of edible plants on earth that would presumably be useful, and it becomes a big problem to choose which of those plants are the best for producing food for astronauts,” explained Carl Lewis, director of the Fairchild Tropical Botanic Garden, which is leading the effort.

“And that is where we come in.” The Miami-based garden has identified 106 plant varieties that might do well in space, including hardy cabbages and leafy lettuces.

They have enlisted 15,000 student botanists from 150 schools to grow plants in space-like conditions in their own classrooms.

The four-year project is about midway through and is paid for by a $1.24 million grant from NASA.

Using trays rigged with lights that mimic the grow boxes used in space, students must tend to the plants and record data on their progress, which eventually gets shared with NASA.