Plants have been grown in soil from the Moon, proving the possibility of an important step for future colonization. However, anyone who expects the Moon to one day represent the food bowl of a depleted Earth should think again – when it comes to fertility, lunar regolith ranks below harsh terrestrial rocks.
Extended Moon missions will be desperate for fresh food and won't want to bring Earth soil to grow them in, so testing the practicality seems like an obvious move. However, the Apollo missions could only bring 382 kilograms (842 pounds) of rocks back, and NASA has allocated them to scientists sparingly, not knowing how long the supply would need to last.
Restrictions are now easing under the expectation the Artemis missions will soon expand the supply. Following the opening of one of the two samples vacuum-sealed since collection, a paper in the journal Communications Biology has announced the first successful floral sprouting in material brought back from the Moon (although the water and air were terrestrial).
Plants have met lunar soil before, Professor Anna-Lisa Paul of the University of Florida, Gainsville noted. “Plants helped establish that the soil samples brought back from the moon did not harbor pathogens or other unknown components that would harm terrestrial life, but those plants were only dusted with the lunar regolith and were never actually grown in it,” Paul said in a statement.
After three applications over 11 years, Paul and Professor Robert Ferl were granted just 12 grams (0.42 ounces) of lunar material to work with. The material was regolith – loose, mixed surface material – less than 1 millimeter in particle size collected by the Apollo 11, 12, and 17 missions, to make growing easier, but the tiny quantity still make the task immensely challenging.
The pair used four plates, each with a sample from each site in separate wells, and added water and a solution containing nutrients the Moon cannot provide. A few seeds of the model organism Arabidopsis were added to each. Matching seeds were planted in soils from hostile Earth environments and materials made to mimic lunar and Martian soil in the days when scientists couldn't access the real thing.
Nearly all the seeds sprouted. “We were amazed. We did not predict that,” Paul said. “That told us that the lunar soils didn’t interrupt the hormones and signals involved in plant germination.” Of course, with so little soil to work with, the seeds' potential growth was limited, but they had managed the hardest part.
On the other hand, the lunar soil plants grew more slowly and reached smaller sizes than the controls, despite similarly limited amounts of material. The damage showed up in other ways as well. “At the genetic level, the plants were pulling out the tools typically used to cope with stressors, such as salt and metals or oxidative stress, so we can infer that the plants perceive the lunar soil environment as stressful,” Paul said.
Although we would expect the Moon to be, in Heinlein's words, a harsh mistress to plants, it's nevertheless concerning it was even worse than hostile Earth soils. More optimistically, the soils were not all equally bad. Plants grew better in the Apollo 17 samples than those from Apollo 12, which in turn beat those collected near Armstrong's famous footprint.
The authors attribute the difference to how exposed the samples had been to the solar wind, suggesting soils from deeper beneath the surface could be kinder on crops. They also hope that growing generations of crops in the same soil may alter them in beneficial ways – after all, it is what brings life to newly formed volcanic islands.