Can Grass and Trees Grow on Mars?

Many books have been written and movies made about the possibility of humans colonizing Mars. Some include descriptions of growing food in habitats or even changing the Martian climate via “terraforming” to enable large scale agriculture. But how realistic is it to think that Earth plants could grow unprotected on Mars today? The short answer is not very.

Although the Martian atmosphere contains abundant carbon dioxide relative to other gases (about 95%), it is very thin. The atmospheric pressure on Mars is less than 1% than it is at sea level on Earth. That’s much less pressure than occurs even at altitudes that commercial airplanes cruise at. You’d have to go more than 25 miles up in Earth’s atmosphere to experience the extremely low pressure that characterizes the thin atmospheric pressure found at the surface of Mars.

One result of this thin atmosphere is that it does not hold heat very well and cools off very quickly at night. While daytime surface temperatures on Mars can reach or exceed freezing in some locations, temperatures at nighttime can fall well below -100 degrees Fahrenheit (below -100 degrees Celsius). So, any unprotected plants on Mars would freeze and die at night. And if that weren’t enough, the thin atmosphere does little to protect the surface from being blasted by sterilizing radiation.

That means that any farming on Mars in the current environment would have to occur in habitats that could provide a denser air pressure and would protect against subfreezing temperatures and excessive radiation. Such habitats would need to be transparent to let in sunlight for plants to grow or would have to come equipped with lights to sustain plant growth.

But what about the Marian “soil?” Could plants grow in it even if protected from the atmospheric elements? Data returned from various missions to Mars indicate that the Martian “soil” has some essential nutrients, but is often rocky, coarse, and deficient in organic matter and other important nutrients such as nitrogen, phosphorous, and sulfur. Nevertheless, studies using simulant soils for Mars have shown that plants can germinate and grow, albeit not as vigorously as on Earth. Plant growth could be facilitated by addition of fertilizers—such was the case in Ridley Scott's popular 2015 film The Martian.

What if humans could change the atmosphere and climate on Mars, making it more hospitable for growing plants as popularized in science fiction such as the Mars Trilogy by author Kim Stanley Robinson? Perhaps one day humans will have the ability to make large scale, wholesale changes to planetary environments. However, given current struggles to control climate change here on Earth, such abilities are far off in the future and our current best bet for growing grass and trees on Mars involves using climate-controlled habitats where the soils are augmented by fertilizer.