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:
Medium hydroponics systems require a physical substance for the vegetables to grow in (in this instance, perlite), whereas solution hydroponics systems only require a liquid nutrient solution.
Essentially you just use perlite or some other soil-less medium in order to support the roots.
Well, for root crops, you need a substrate, and of suffient depth, to support the roots. Root crops are very nicely grown in an "ebb and flow" system. This set up alternately floods and drains the growing media on cycles. The cycle times are matched to the rate of development of the plants so they have enough water, but enough air-time for the roots as well. The ideal substrate is somewhat moisture re-tentive: not a soggy mass (remember the need for airation of the roots- gotta breathe!) but rather having a lot of surface area and air spaces that take a while to dry out. Options could be well- draining soiless mizes, some of the smaller-sized clay marble-type substrates. Maybe sand - it's cheap of course- but old school. You could experiment with it though. Amazon.com has some good DIY books to do it on the cheap. DO NOT SPEND THOUSANDS FOR A SET UP (unless you have tons of dough- in which case why not? :)- you can make nice, much larger setups for less than $200.00. Hydro is exceedingly cool - Have Fun!