You might think that sub-irrigation setups sound a lot like hydroponics. But there are differences . Hydroponics implies that your plants get their nutrients from the water solution you use. Sub-irrigation is a term that describes how the water is delivered to your plants. Some people might say that the difference is in the absence of soil for hydroponics systems and the use of growing media for sub-irrigated systems. But there are hydroponics systems that use pebbles, coconut husk, and perlite. These systems are passive sub-irrigation types, and the materials are only used for the structure and serve as the wick that will bring the water to the plant's roots. The growing media doesn't have nutrients, so the plants get their nourishment from the water. On the other hand, hydroponics systems may be under-irrigated, or you might pour water on them from above.