Greenhouse operations are the most intensive commercial plant production environments, typically producing between 1-3 million plants per acre each year. Plants are grown in production cycles, with many operations producing 3-4 cycles of seasonal plants each year.
Plants can be grown in ebb-and-flood systems (shown at right), on benches or on ground pads. Typically greenhouse systems in the United States use very high-tech environmental control systems to heat, cool and dehumidify the greenhouse environment. In more northern latitudes, intense lighting sources are used to extend natural daylight.
Nutrients are most often applied in tandem with the irrigation water(called fertigation) to minimize any restrictions on growth due to nutrient stress.
Given the cost of energy and labor, greenhouse systems are only used to produce the most high-value crops in the United States, in contrast to more sub-tropical or tropical climates, whose more moderate temperatures and longer daylength allow for the production of many other greenhouse crops, year round.