Future Martian colonists may have a tough time growing crops to eat, the Science News website reports.

Scientists recently tried planting lettuce and a weed, arabidopsis thaliana, in three kinds of Martian-type dirt. One type was made of material from Hawaii and another type from the Mojave Desert - both resemble the kind of dirt found on Mars. The third was created from volcanic rock, clays, salts and other chemicals observed by NASA’s Curiosity rover.

The lettuce and the weed both grew in the natural Martian-like soils under controlled lighting and temperature conditions when fertilized with a cocktail of nitrogen, potassium, calcium and other nutrients; but failed in artificial dirt. The reason: Terran soil contains microbes and organic material that helps plants grow, but the dirt of Mars is composed of crushed rock and nothing more, meaning that potential Martian colonists will have to put a lot of work into transforming it into soil that will sustain plant growth.