Growing mushrooms? You won’t need much sunlight. You won’t even need soil. At one mushroom farm in Brussels, Belgium, growers need just water, barley, and a basement.

Quentin Declerck works at Le Champignon de Bruxelles mushroom company. He guides visitors through the basement where mushrooms grow. “On the right side you have a nameko production,” he says. He explains: Nameko is an orange, gluey mushroom. It goes into Japanese dishes like miso soup.

Mushrooms like to live in warm, dark spaces. In the mushroom basement, temperatures never go below around 50 degrees Fahrenheit. Nameko mushrooms, mild oyster mushrooms, and rich-tasting shiitakes grow well. The farm produces five tons of mushrooms each month. (That’s about the weight of two rhinoceroses.) 

What makes the basement mushrooms thrive? All mushrooms develop on a substrate. A substrate is any material on which a mushroom’s mycelium (roots) can grow. Any mushroom farmer has to find the perfect substrate recipe. That can be hard. People use straw, sawdust, manure, and coffee grounds. But they have to make sure their substrates are clean. (Guess what else loves warm, dark, wet spaces? Bacteria and mold do—exactly what mushroom farmers don’t want. Heating a substrate kills these invaders before they can grow.)

In the Brussels basement, the mushrooms feed on barley recycled from a local brewery. In cities, this waste usually gets thrown away. 

The urban farmers grow microgreens in the basement too. Microgreens are greens harvested when small. Chefs at fancy restaurants use microgreens to beautify dishes. City chefs pair the basement mushrooms and greens. 

Mushrooms: They’re not fruits and they’re not vegetables. Some can nourish you with vitamin B, copper, and potassium. Others—toadstools—can kill you. And the basement mushroom farm just keeps recycling. Once the mushroom harvest ends, the material it fed from can be used again. This time it turns into fertilizer for other crops. Champignon de Bruxelles growers give it to local farmers for free.