So, you're intrigued by the concept of sowing and growing sans soil, but not sure what type of setup makes sense. This section gives an overview of some general types of commercial and homemade hydroponic systems suitable for the classroom. If you want to do short-term explorations, raising crops like lettuce, herbs, houseplants, or annual flowers, consider a basic system like those pictured in Simply Super School Setups. If you have visions of producing mature fruiting plants like tomatoes, cucumbers, and so on, consider purchasing a commercial hydroponic unit or finding a design for a more sophisticated unit. There are a range of designs for hydroponic systems. Some use media, while others use only water. Some recycle nutrient solutions, while others rely on regular flooding with fresh solution.
The following descriptions and pages explain key hydroponic system terms and some general types of systems used commercially and by home gardeners.
These systems use no energy to move nutrients and water. They can be as basic as a perlite-filled flowerpot that is hand-watered regularly with nutrient solution. Passive systems often use a "wicking" material to draw up the liquid nutrients, or they simply suspend the plants in the solution with an air space around some of the root zone. They can be media-based or pure water-culture systems.
A hydroponic system is active if it relies on some type of energy (usually electricity via a pump) to move the nutrients in and out of the root zone area and to provide aeration. These systems, which can also be either media- or water-based, are generally used for larger plants (e.g., tomatoes and cucumbers) and tend to be more sophisticated. In recirculating or recycling systems, the nutrient solution is conserved by being recirculated either manually or electrically through the medium. These systems require closer monitoring of pH, nutrient concentration, and so on. Systems with pumps to aerate and deliver more oxygen to roots tend to produce healthier plants more quickly than do passive systems.