Organic – Chemical compounds containing the element carbon other than the inorganic carbonates. Often refers to any part of, or anything produced by, plants or animals.

Organic Matter (Soil) – A portion of the soil consisting of substances derived from the life and death of plants, plant parts and other soil organisms.

Overseed or Overseeding – The process of incorporating seed into an existing lawn area for the purpose of lawn repair or introduction of different grass species.

Particulate – Used as a characterization of very tiny pieces (particles) of matter, (e.g., dust and soil)

Patch Disease - A non-specific term applied to small dead, circular areas in a lawn caused by a number of different pathogens. Symptoms may also include the appearance of dead rings of grass with green grass inside and outside of the ring.

Pathogen (Plant) – Usually applied to a microorganism with the capacity to cause a plant disease.

Peat – A partly decomposed plant material found in marshy areas. Identification or origination of parent plant material may still be possible (e.g., sphagnum peat moss).

Perennial – Plants that live two or more years producing flowers and seeds in successive years.

Permeable – Allowing water or other substances to pass through or infiltrate (e.g., a permeable surface such as a lawn).

Pest (Plant) – Any insect, mite, rodent, nematode, fungus, weed, or other organism capable of causing plant stress, injury or death through disease, consumption of the plant or competition.

Pesticide – Any chemical (or mixture of chemicals) or biological agent used to control plant or animal pests in order to protect and/or preserve desirable plants.

pH – A numerical measure of soil acidity or alkalinity based on the hydrogen ion (H⁺) concentration in the soil. A pH of 7 indicates neutral conditions (neither acidic or alkaline); above 7 is basic (alkaline), below 7 is acidic.

Phenoxy-Type Herbicides – A category of systemic weed killers that have a chemical structure composed of six carbon atoms joined together in a ring formation. Two examples are 2,4-D and mecoprop (MCPP).

Phosphorus – One of the major plant nutrients; important in root growth and plant energy functions. The middle number of a fertilizer analysis N-P-K.

Photosynthesis – The chemical plant process where carbohydrates are formed by combining carbon dioxide and water in the presence of light; occurs in the chlorophyll containing parts of the plant (i.e., leaves and stems).

Plant Competition – The interaction between plants for light, moisture, and soil nutrients.

Pollination – The transfer of pollen from the stamen (male portion of the flower) to the stigma (female portion of the flower). May occur within the same flower, different flowers on the same plant or different flowers on different plants.

Pollution – The process of contaminating air, water or land with impurities to an undesirable level; results in decreased benefits from the environment.

Postemergence – Generally refers to the application of an herbicide after the weed has emerged (and is usually visible) from the soil.

Potassium – One of the major plant nutrients important in maintaining general plant health and vigor. Often associated with improved stress and disease tolerance. It is the third number in the fertilizer analysis N-P-K. See N-P-K.

Preemergence – Generally refers to the application of an herbicide before the weed emerges from the soil. Target plants are most often not visible above ground at the time of application.

Pupa – The resting or transforming stage of an insect that goes through four lifecycle stages (i.e., egg, larva, pupa, adult) in its development.

Pure Live Seed (PLS) - A seed lot's percentage of seed that is pure and viable.

Purity - The degree of cleanliness or freedom (expressed as a percentage) from weed and other crop seeds.

Quick-Release Nitrogen Source - Nitrogen from these sources is available for use by the plant as soon as water is applied and the fertilizer granule dissolves. Can also be applied in liquid formulations. Plant responds with quick green-up and rapid rates of growth.