Q How do plants grow without dirt?
— Ruby Taggart, Merrimac, Wis.
A Simon Gilroy, professor in the department of botany at the University of Wisconsin-Madison:
The principal purpose of soil is to provide mineral nutrition for the plant. About 20 elements make up the mineral nutrition requirements for plants, and if you can provide those, you’re providing a lot of what soil is giving to the plant.
A long time ago, plant researchers found out that you can get plants to grow perfectly fine without soil if you provide water and the mineral nutrition. That’s the idea of hydroponics, where we can grow plants in a soil-less environment. We’re providing what they need: water and the minerals that allow them to grow.
Soil also provides structural support, so to replace soil we have to provide support in some other way. The classic way for hydroponics is to have plants growing in a plug, some inert material that provides the support. The roots grow down into a liquid. The liquid provides the minerals that the plant needs. All you need at that point is to power plant growth by photosynthesis, which is providing it with air and sunlight.
You can take that to the extreme. Some of the research being done at UW-Madison is related to figuring out how plants can be optimized to grow in space. Researchers are interested in growing plants in the space station to perhaps sustain astronauts for incredibly long journeys.
But growing in that weightless environment is not how plants evolved. Think about growing plants off the Earth where there is no soil. Think about growing them, for instance, on Mars or on the moon, where you can grow them in the dust that coats the surface of those bodies.
Providing you can balance the unique environment and added stresses, maybe add a little bit of fertilizer, you can grow plants perfectly happily under those conditions.
With minerals, water, sunlight and air, you can make a plant grow.