Hydroponics means growing plants without soil. The roots sit in water instead, and that water carries the nutrients a plant would normally find in the ground.
In many systems the water runs in a thin stream along channels, past the roots, and back to a tank, so the same water is used again and again. The plants are held in small cups, often in a soft growing medium, with their roots hanging down into the flow.
Without soil the leaves stay clean — there is no mud splashing up when it rains — and many soil pests and diseases have nowhere to live. Growth is steady, because the roots always have water and food within reach.
Leafy crops such as lettuce suit hydroponics especially well. They grow quickly, they do not need deep roots, and clean leaves need less washing in the kitchen — just right for green and red coral lettuce.