One day, we could be growing the fruit in space. 

growing produce in urine
Credit: © DLR

There are many secrets to growing plump, juicy tomatoes, but never have the instructions included adding urine—until now. In laboratories at Germany’s aerospace center, scientists are cultivating the red fruit in tanks filled with golden…urine—an experiment they say could one day lead to feeding colonies of people on the moon or even Mars.

Food noshed on beyond the boundaries of the Earth’s atmosphere is currently carried on rockets or shuttled to the International Space Station, save for a few hunks of lettuce some ambitious astronauts have grown in hydroponic solutions. But that doesn’t mean that space travelers won’t one day have a need to grow their own vegetables and fruits, so scientists in Germany’s space program are working to figure out how they can make that happen.

In space, water for consumption often comes from astronauts’ urine and sweat. (Don’t worry—it’s purified first.) So, the scientists argue, if we can use urine to make clean drinking water, certainly we can use it—and the salt it naturally contains—to grow a self-sustaining food supply.

“The Earth is a closed biological system with plants producing oxygen and food, then you have the animals and the microbes to produce all the degradation processes in the soil,” Jens Hauslage, a scientist involved in the project, told the BBC. “Without these systems, no sustainable long-term life-support system will be viable.”

In the scientists’ offices, tanks are filled with artificial urine—so the researchers can know the exact composition of the liquid—and columns lined with pumice stone, which contains bacteria. As the BBC reports, the microbes in the bacteria feed on the urine, turning the urine’s ammonia into nitrites and, eventually, an effective fertilizer. In fact, a BBC reporter who toured the tanks swears the tomatoes are totally edible—if a little bitter.

Perhaps even better, the writer reports, the tanks carry no smell. That’s because the urine is converted to ammonia so quickly it can’t stink the place up, so to speak, Hauslage says.

Next, the German space program will take the tanks into orbit: At some point later this year, the agency will launch its Euglena and Combined Regenerative Organic Food Production in Space (EU:CROPIS) mission, according to the BBC, a meter-wide satellite that’ll contain two greenhouses complete with these tomato-growing urine tanks. Once in orbit, the satellite will spin to mimic the gravity on the moon—and later, to simulate Mar’s gravity.

“After launch, we’ll spin the satellite and water the system,” Hauslage told the BBC. “The tomatoes will germinate and we’ll feed the system with urine to produce tomatoes.”

Scientists will monitor the plants’ progress through 16 cameras. Data will be sent to Earth at least four times a day. And of course, if successful, this experiment could just be the start of a more robust interplanetary agriculture system.