Passive Systems

Passive hydroponics systems have a lot of advantages. You might ask: "What's a passive system?" The short answer is one that doesn't need electricity to operate. The two easiest passive systems are 1) wick systems, and 2) float systems. There is a third form of passive system which is a bit more technically sophisticated, but not much, called an Autopot system. Let me quickly summarize each.

Wick Systems

Wick system are two level systems. The nutrient is in a tank below a cover and the plant is mounted on the cover with wicks which go down into the nutrient tank. The nutrient feeds up to the plant by capillary action and the roots of the plant follow the nutrient moisture down into the tank. It is completely passive and very easy to construct. Plants don't typically grow as vigorously in a wick system as they do in an NFT system, but they do well.

Float Systems

Float systems are usually best suited for plants that are fairly light since heavy plants with substantial support requirements will tend to weigh down the floats and submerge the system or the floats will have to be large. I have used floats very successfully to grow basil and lettuce. You get Styrofoam sheets to make the floats and cut holes for little plant cups in the foam. Since the system actually floats on the nutrient the bottom of the cups are in the nutrient so while you could use wicks they are generally unnecessary. Rather quickly the roots grow down into the nutrient. You can oxygenate the solution using aquarium air pumps but then you need electricity. My experience suggests that if you design your plant cups so there is a relatively dry interval they can get oxygen via that route. There's a photo of a float system growing basil in the sidebar.
I'll leave the Autopot system for my next post, since it is more complicated and deserves its own discussion.