Greenhouse Management
Glossary
E
EBB-AND-FLOW SYSTEM – A cultural system in which containerized plants are grown in a watertight bench top. When watering is required, nutrient solution is pumped into the bench to a depth of 0.5 to 0.75 inch (13 to 19 cm). The solution is drawn into the root medium by capillarity. When the pot is thoroughly wet, after about 10 to 15 minutes, the nutrient solution is drained from the bench to a holding tank where it is stored until needed by the crop again. This is a closed cultural system.
ECONOMIC THRESHOLD – The level at which pest damage justifies the cost of control. In home gardening, the threshold may be aesthetic rather than economic.
EMITTER – Also known as a dripper. Used in drip irrigation to control the flow of water into the soil.
EMULSIFIER – Chemical that allows petroleum-based pesticides like emulsifiable concentrates (EC's) to mix with water.
EMULSION – A mixture of two or more liquids that are not soluble in one another. One is suspended as small droplets in the other.
ETIOLATED SEEDLINGS – Stretched, leggy seed lings resulting from exposure to a very low light intensity.
EVAPORATION – The loss of water from the soil surface as vapor.
EVAPOTRANSPIRATION – The combined processes of evaporation and transpiration.
EVEN SPAN GREENHOUSE – These are single houses that have roofs with an even pitch and an even width. They have pitched roofs like a house with straight sides and two gable ends. The framework is usually made from wood, aluminum or steel. The covering tends to be permanent or semi-permanent material like glass or structured sheets.
