• Iceburg lettuce got its name from the fact that California growers started shipping it covered with heaps of crushed ice in the 1920s. It had previously been called Crisphead lettuce.

The floating gardens of the Aztecs of Mexico and the hieroglyphics of ancient Egypt describe growing plants in water. Some even speculate that the hanging gardens of Babylon were in fact hydroponic. (Resh) Although we have ancient accounts, John Woodward is the first person accredited for growing plants in liquid medium (1699). In the 1860’s, German scientists Sachs and Knop organized the first liquid solution into a research science technique. William Gericke of University of California Berkeley was the first hydroponic user to produce crops with the method. (Bugbee/Hershey)

The word “Hydroponics” refers to two Greek words, “water” and “working.” It is defined as the science of growing plants without soil.

In order for hydroponics to provide for the five basic needs of plants which are air, nutrients, water, light, and anchorage, some changes need to be made from traditional crop production. An aquarium pump provides the oxygen in a static hydroponic culture. The method of aerating the roots is not as important as the movement of the water over them. Nutrients are provided by a nutrient solution added to the jar. It must be checked every few days to maintain optimum pH levels. Water is provided along with the nutrient solution. Light is provided by the sun or artificial light. Anchorage is provided by a sponge or other material holding the plant in suspension above the nutrient solution.

Nutrients are essential to plant growth because they provide a constant source of food and energy. Without nutrients, the plant will not complete its life cycle in a normal manner. With prolonged deficiency, the plant will not survive. The primary nutrients involved in plant growth are nitrogen (N), phosphorus (P), and potassium (K).

The effects of these nutrients can be visually observed under many conditions:

Nitrogen (N)

• Optimum: Plants with the optimum amount of N are dark green and high in protein content.
• Deficient: Nitrogen deficiency is detected by a light green color. The lower leaves turn yellow and brown as they dry up. The plant is stunted, making the stem short and slender.
• Excess: Too much N will cause the plant to become very leafy. Flowering will be delayed.

Phosphorus (P)

• Optimum: P stimulates root formation and growth, provides plants with a healthy start, and stimulates flowering and seed development.
• Deficient: Phosphorus is needed for growth and flowering. If P is not provided, the plant grows slower and delays flower and pod development. The leaves in a P deprived plant are dark green with purple or red appearing along the veins. The lower leaves turn yellow and brown as they dry up. The plant stem becomes short and slender.

Potassium (K)

• Optimum: At optimum levels, K increases vigor and disease resistance. It also is important for the formation of starches, sugars, and translocated sugars.
• Deficient: Chlorotic (yellowing) leaves result from K deficiency. Necrotic (tissue death) spots between the veins, margins, or leaf tips appear. The plant stem becomes slender.

Information about the NPK effects is provided by the Wisconsin Fast Plants Program, University of Wisconsin, Department of Plant Pathology. Investigating Plant Physiology. Copyright 1989. Carolina Biological Supply Company.

The students will construct and monitor their own hydroponic system by following the instructor’s directions and prompting. Form groups of two or three students for this project.

Objectives

• Describe the five requirements that plants need to survive.
• Explain the three primary nutrients (macro elements) required by all plants.
• Define hydroponics.
• Construct and monitor a hydroponic system.

If desired, have a volunteer complete steps 5 and 6 of Part 1 on Handout A.