Hydroponics is the method of growing plants in a soil-less medium. I've always wondered, how does someone grow a mainly root/bulb-based vegetable (potato, turnip, onion, etc) in a hydroponic environment?
"Soil-less" doesn't necessarily mean "liquid", though I often think liquid when I hear hydroponics.
See, for example, this page on growing hydroponic carrots:
Essentially you just use perlite or some other soil-less medium in order to support the roots.