Natural enemies : Predators, parasites, or pathogens that are considered beneficial because they attack and kill organisms that we normally consider to be pests.

Necrosis : Death of tissue accompanied by dark brown discoloration, usually occurring in a well-defined part of a plant, such as the portion of a leaf between leaf veins or the xylem or phloem in a stem or tuber.

NPK : Initials for Nitrogen-Phosphate-Potash.

Organic : Material which is either plant or animal in origin.

Ornamental Grasses : Any of various plants having slender leaves characteristic of the grass family.

Oviposit : To lay or deposit eggs.

Oviposition : The laying or depositing of eggs.

Parasite : An organism that derives its food from the body of another organism, the host, without killing the host directly; also an insect that spends its immature stages in the body of a host that dies just before the parasite emerges (this type is also called a parasitoid).

Pathogen : A disease-causing organism.

Peat : Partly decomposed moss plant which grows in moist areas in the north.

Penjing : Is the ancient Chinese art of growing trees and plants, kept small by skilled pruning and formed to create an aesthetic shape and the illusion of age. Penjing is very similar to (and a

Precursor : The Japanese art of bonsai. Penjing trees are commonly kept outdoors, in gardens, and tend to be trained larger than the bonsai style. It is also in the Penjing style to create groupings of trees, creating a scene of a forest, rather than an individual tree.

Pergola : Is a garden feature forming a shaded walk or passageway of pillars that support cross beams and a sturdy open lattice, upon which woody vines are trained.

Permaculture : Is the practice of designing sustainable human habitats by following nature's patterns.

Pesticide : Any substance or mixture intended for preventing, destroying, repelling, killing, or mitigating problems caused by any insects, rodents, weeds, nematodes, fungi, or other pests; and any other substance or mixture intended for use as a plant growth regulator, defoliant, or desiccant.

Pesticide Resistance : The genetically acquired ability of an organism to survive a pesticide application at doses that once killed most individuals of the same species.

Perennial : A plant that grows year after year as are most trees, shrubs, grasses, and some smaller plants.

pH : The measurement of the acidity and alkalinity of a material. It ranges from 0 to 14, with 7 being neutral. 0-7 indicate acidity, 7-14 indicate alkalinity.

Pheromone : A substance secreted by an organism to affect the behavior or development of other members of the same species; sex pheromones that attract the opposite sex for mating are used in monitoring certain insects.

Phosphate : The fertilizer form of phosphorus. Usually considered the actual flower producing mineral.

Photosynthesis : The process by which plants convert sunlight into energy.

Potash : Usually made from wood ashes. One of the three main minerals in fertilizer. A term used to denote potassium.

Postemergence Herbicide : Herbicide applied after the emergence of weeds.

Potassium magnesium sulfate : Also called Sul-Po-Mag and langeinite. Mined mainly in New Mexico and some european countries. Use in areas that lack these minerals.

Predator : Any animal (including insects and mites) that kills other animals (prey) and feeds on them.

Preemergence Herbicide : Herbicide applied before emergence of weeds.

Protozoa : One-celled microscopic animals needed to help breakdown organic matter.

Pruning : Is the practice of removing diseased, overmature, or otherwise unwanted portions from a woody plant. Pinching back herbaceous plants, such as chrysanthemums to encourage denser growth or more profuse or delayed flowering, is a form of pruning.