We’re a long ways away from colonizing another planet—depending on who you talk to—but it’s not too soon to start understanding how we might do it when the time comes. Growing enough food will be one of the primary concerns for any future settlers of Mars. With that in mind, researchers at the Wageningen University and Research Centre in the Netherlands have created simulated Martian soil and used it to grow food crops.

This is actually the second experiment the team has performed with simulated soil, and the results were promising. The team harvested not only tomatoes and peas, but also rye, garden rocket, radish, and watercress. But it’s not just the edibles that were promising, it was the overall ability of the simulated soil to produce biomass in general. According to the researchers, the soil produced biomass equal to that produced by Earth soil, which was used as a control.

The team also grew crops in simulated Moon soil, to understand how that soil performed, but it produced much less biomass, and only the humble spinach was able to grow in it. The simulated Martian and Lunar soils were provided by NASA. The Martian soil came from a Hawaiian volcano, and the Lunar soil came from a desert in Arizona.

The soil used was not exactly the same as the soil you would scoop up if you were on the Moon or Mars. It was amended with organic matter in the form of manure and fresh cut grass. While this may sound like a ‘cheat’, it’s no different than how gardens are grown on Earth, with gardeners using manure, compost, grass clippings, leaves, and even seaweed to provide organic matter.

Of course, none of these soil amendments will be available on the Moon or Mars, and we won’t be sending a supply ship full of manure. Colonists will have to make use of all of the inedible parts of their crops—and human feces—to provide the organic material necessary for plant growth. It’ll be a closed system, after all.

The crops were grown in a controlled environment, where temperature, humidity, and other factors were kept within Earthly parameters. Any crops grown on Mars will be grown in the same controlled environments, at least until genetic modification can create plants able to withstand the increased radiation and other factors.

A problem facing colonists trying to grow food on Mars is the heavy metal content of the soil. Mars soil contains mercury, lead, cadmium, and arsenic, which are all toxic to humans. The presence of these elements doesn’t bother the plants; they just keep growing. But any crops grown in this soil will have to be tested for toxicity before they can be consumed. This is the next experiment that the team has planned.

Researchers at the Wageningen University are currently crowdfunding for this next experiment. If you’d like to contribute, check out their page here.