Hydroponic gardening is a method of growing plants without soil. The plant is either grown in a soilless substrate that has been saturated with a liquid nutrient mix, or exclusively in a nutrient mix and supported from above. Studies conducted at the University of Arizona have shown that plants grown hydroponically thrive better and produce a higher yield of crop than plants grown in soil.
The first plants grown hydroponically may have been in the Hanging Gardens of Babylon. According to the Greek historians Strabo and Diodorus Siculus, King Nebuchadnezzar II commanded the construction of the gardens for his sick wife, who longed to see the fertile plants of her native Persia. The gardens were created as an artificial mountain in the desert kingdom of Babylon. Construction is thought to have been made of bricks baked in the sun, and then channels for the plants were lined with lead and filled with water from the nearby Euphrates river.
The actual theory behind hydroponics was first outlined by Leonardo DaVinci, who observed that plants need mineral elements to grow. 100 years after DaVinci's observations, a Belgian scientist named Van Helmont documented that plants absorb minerals through water. In the 1860s the first scientists began experimenting with growing plants exclusively in water. The most significant advancements in nutriculture were made during the 1930s when the Great Depression and the American Dust Bowl had scientists scrambling for ways to boost crop yields. During this time, the term nutriculture was abandoned in exchange for the term hydroponics, and advancements were made toward adapting the process from the lab and into commercial farms.
Plants grown hydroponically may be grown in a soil free substrate such as vermiculite or rockwool. These substrates are typically free of any nutrients, but may provide support and anchoring to the root system of the plant. However, plants may also be free-floating in liquid nutrients. Usually the root system is suspended in a chamber filled with the liquid nutrients, while the actual plant grows out of the chamber through a collar or hole in the lid of the chamber. Low-growing plants such as lettuce or some herbs receive all the support they need from this collar. Taller plants such as tomato or cucumber vines require additional support in the form of trellising. The nutrient chamber may also contain some kind of aeration system to supply the roots with oxygen as well.
Hydroponic plants seem to thrive over soil-grown plants because plants grown in a hydroponic solution receive all of the nutrients that they need when they need them. Plants grown in soil have to search for nutrients, and often do not receive all of the nutrients they require. Plants that are grown in a hydroponic solution are not limited by the soil conditions in the areas where they are grown. Because of this, vegetables and fruits have been grown hydroponically in large urban areas as well as in scientific outposts in the Antarctic.
Any plant that grows in nature can be grown hydroponically. The limiting factors for plants that are grown hydroponically are typically external factors, such as availability of nutrients and plant support structures. For this reason, easy-to-grow plants such as lettuces or herbs and tomatoes are more frequently grown than fruit trees and other plants which may be harder to care for. Hydroponic herbal systems are frequently sold commercially for use in countertop kitchen gardens, and the University of Alabama has in the past sponsored a hydroponic tomato growing challenge.