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Facultative long- and short-night plants Plants that do not require a night length longer or shorter than a given critical length for a response to occur, but that will respond faster if the dark period is longer or shorter respectively than a critical length. (Nelson, 2003)

Fan-and-pad cooling system A system for cooling greenhouses used during the warm months of the year. Warm air expelled thought exhaust fans in on wall is replaced by air entering trough wet pads on the opposite wall. The entering air is cooled by the evaporation of water in the pad. (Nelson, 2003)

Fan-tube cooling A system for cooling greenhouses used during the cool months of the year. Cold air entering though a louver high in the gable of the greenhouse is directed along the length of the greenhouse though a blear plastic distribution tube. Pairs of holes space equidistant along the length of the tube’s opposite vertical walls permit uniform air distribution throughout the greenhouse. (Nelson, 2003)

Fasciation A malformation in plant stems resulting in an enlarge and flattened stem, as if several stems were fused. (Nelson, 2003) Read more about fasciation.

Fertigation The combined application of watering and fertilizer such that fertilizer solution is applied every time the plants require water. (Nelson, 2003)

Fertilizer proportioner (fertilizer injector) Equipment used to inject concentrated fertilizer solution into a water line to result in a desired dilution prior to plant application. (Nelson, 2003)

Fixation The process or processes in a soil by which certain chemical elements essential for plant growth are converted from a soluble or an exchangeable form to a much less soluble or nonexchangeable form. (Nelson, 2003)

Fixed costs Costs of conducting business that are not directly related to the number or type of items produced. Interest on a greenhouse mortgage, for example, is fixed because it remains unchanged if poinsettias are grown rather than azaleas, or even if no crop is grown. (Nelson, 2003)

Flat A container used in greenhouses and nurseries for purposes such as germinating seeds or for holding several small plant containers. Flats are commonly constructed from wood or plastic. They are variable in size commonly approximate 21 inches (53 cm) long by 11 inches (28 cm) wide by 2.5 inches (6 cm) deep. (Nelson, 2003)

Floor heating Application of heat in or near the floor of a greenhouse. (Nelson, 2003)

Floriculture The art and science of growing and utilizing plants valued for their aesthetic characteristics other than woody plants used in the outdoor landscape. (Nelson, 2003)

Flowering plants Greenhouse crop plants grown in a pot an sold in the flowering state. (Nelson, 2003)

Fog cooling A system for cooling greenhouses in which fog is generated inside the greenhouse, AS the fog droplets evaporate, heat is absorb, thus cooling the air. (Nelson, 2003)

Foliage Plants Plants sold for the ornamental appearance of their leaves. Also referred to as Green Plants. Ferns are marketed in this group.

Foot-candle (fc) A unit of illumination equal to the direct illumination on a surface everywhere 1 foot from a uniform point source of 1 international candle. It is equivalent to 10.76 lux. (Nelson, 2003)

Forced-air heater A heater containing a heat source, a heat exchanger, and a fan for expelling the heated air. (Nelson, 2003)

Fresh flowers Flowers marketed subsequent to being cut from commercial crops. (Nelson, 2003)

Fritted nutrients Nutrients, usually potassium or micronutrients, contained in a solid, finely ground glass powder, The glass slowly dissolves in the root medium, releasing nutrients over an extended period of time. (Nelson, 2003)

FRP (Fiberglass-reinforced plastic) A type of panel used as the transparent covering on some greenhouses. (Nelson, 2003)

Fungicide An agent or preparation used for killing fungi. (Nelson, 2003)

Fungus A eukaryotic, multicellular, filamentous, branched microorganism. (Nelson, 2003)

Learn more about fungi and other pathogens that lead to plant disease at APSnet.