Greenhouse Management
Glossary
P
PATHOGEN – An organism that causes disease in other organisms.
PEAT POTS – Plant pots made of compressed peat moss and paper.
PELLETED SEED – Small seed, such as petunias, which have been coated with an inert material such as clay to make them easier to handle.
PENETRANT – Chemical that helps a pesticide active ingredient to get through a surface and into an object or organism.
PERORATED POLYETHYLENE TUBING – Plastic tubing 18 to 24 inches (45 to 60 cm) wide, with regularly spaced holes on each side used to distribute air in a greenhouse.
PERENNIAL –A plant that lives for three or more seasons. Perennials may not bloom the first season planted, especially ones that are shipped bareroot.
PERLITE – Perlite is a substance made from volcanic rock. It is white, light weight and often used as a soil additive to increase aeration and draining of the soil.
PESTICIDE – Any substance which alone, in chemical combination, or in any formulation with one or more substances is defined as a pesticide in section 2(u) of the Federal Insecticide, Fungicide, and Rodenticide Act (7 U.S.C. 136(u) et seq).
ph – The acidity or alkalinity of a solution on a scale of 0-14, with a value of 7 signifying neutral, values below 7 signifying acidic, and values above 7 signifying alkaline. Relates to the concentrations of hydrogen (H+) ions in the soil. pH values are logarithmic.
PHEROMONES – Chemicals emitted by an organism to influence the behavior of other organisms of the same species.
PHOTOPERIODISM – The response of a plant or animal to the relative length of day and night. The response in plants can take on many forms, including flowering, changes in leaf shape or internode length, and bulb or tuber formation.
PHOTOTROPISM – Response shown by plants to light coming from one direction.
PLANTING STOCK – Any plant or plant tissue other than annual seedlings but including rhizomes, shoots, leaf or stem cuttings, roots, or tubers, used in plant production or propagation.
PLUGS – Young perennials or grasses used to cover large areas of beds or lawns; so-called because they are "plugged" into small holes drilled or dug into the soil.
PLANTING STOCK - Any plant or plant tissue other than annual seedlings but including rhizomes, shoots, leaf or stem cuttings, roots, or tubers, used in plant production or propagation.
POLYETHYLENE – A plastic material used in the greenhouse industry in the form of thin films for covering greenhouses. It is an inexpensive substitute for glass. Generally, two layers are used- an outer layer 6 mils (6 one-thousandths of an inch) thick and an inner layer either 4 (0.10 mm) or 6 (0.15 mm) mils thick.
POUNDS PER SQUARE INCH (PSI) – Psi is a unit of measure (literally the amount of pressure applied to each square inch of surface) used to describe the water pressure inside pipes, tanks, etc.
PRESSURE – The measurement of force within a system. This is the force that moves water through pipes, sprinklers and emitters. Static pressure is measured when no water is flowing and dynamic pressure is measured when water is flowing. Pressure and flow are affected by each other. [bars, psi, kPa]
PRESSURE REGULATOR – A device that maintains a constant downstream pressure (cannot increase pressure).
PRESSURE-TREATED LUMBER – Lumber treated under high pressure with chemicals that protect it from decay.
PROPORTIONER – A mechanical unit that dilutes a small amount of concentrated fertilizer stock solution into a large volume of water.
PUMICE – Pumice is a type of volcanic rock consisting of mostly silicon dioxide and aluminum oxide with small amounts of iron, calcium, magnesium, and sodium.
PUMP EFFICIENCY – Ratio of the water power produced by the pump to the power delivered to the pump by the motor.
PURLIN – Longitudinal members of the structural framework that support the glazing material on the roof.
