If humans ever set up permanent bases on the Moon or Mars, we'll need to be able to grow our own food there. To find out whether that's actually possible, a team of scientists in the Netherlands planted 14 plant species in soils that simulate the Martian and lunar regolith. It turned out that the Martian soil simulant was better than some Earth soils for growing plant life, which is good news for astronauts. There are a few caveats, but we'll get to those later.
First, you're probably wondering what the heck is a soil simulant, and where does it come from? NASA makes them out of our very own terra firma, and you can buy your own here. (Cost: $7.50 for 2 ounces.) The Mars simulant (PDF) comes from a volcanic cone in Hawaii, and has a chemical composition similar to the Mars dirt that the Viking 1 lander analyzed. The Moon simulant (PDF) comes from volcanic ash deposits near Flagstaff, Arizona.
Real Moon and Mars soils appear to contain the essential ingredients that plants need, except for reactive nitrogen (and an abundant water supply). Though the simulant soils closely match the composition and grain size of the real stuff, they also contain trace amounts of the nitrates and ammonium—the nitrogen-based compounds that plants love. So the simulant soil isn't a perfect model.