Plant Growth Regulator (PGR)

Last Updated: February 26, 2019

Definition - What does Plant Growth Regulator (PGR) mean?

A growth regulator, plant growth regulator, or PGR, is a natural or synthetic chemical that is sprayed or otherwise applied to a seed or plant in order to alter its characteristics. They are sometimes referred to as plant hormones.

Growers can add PGRs to their crops in order to achieve a desirable goal, ranging from increasing insect and disease resistance to increasing root strength. Some PGRs also are used to stunt growth.

MaximumYield explains Plant Growth Regulator (PGR)

Growth regulators can be either organic (naturally derived) or synthetic. Organic sources of PGRs includes naturally sourced amendments such as seaweed and liquid kelp. Commercial growers, including nurseries, generally use synthetic growth regulators.

Currently, there are five classes of PGRs, including auxins, cytokinins, gibberellins, abscisic acid, and ethylene. Each type of growth regulator has a different effect on plants.

Auxins are responsible for plant cell elongation and have an effect on rooting, as well as tropic responses and bud development. Cytokinins can be used to stimulate or retard plant growth and are sometimes used as antagonists for auxins. Gibberellins help to stimulate flowering within plants and can play a role in root formation. Abscisic acid dictates germination and water stress management, while ethylene is used in conjunction with root development and shoot growth.

Not all plant growth regulators are designed to foster faster growth. Some are designed to slow down growth and keep young plants compact for easier transportation and transplantation for longer periods. This is important for commercial growers who sell seedlings to at-home gardeners, and ensures not only easier transplantation, but also helps nurseries achieve shorter plants that are not easily tangled, bent, or otherwise damaged.

When used according to prescribed agricultural practices, these hormones are not known to be harmful to humans, but when applied outside of those guidelines, they can cause problems with excessively fast growth, including external fruit ripening prior to interior ripening, and residual PGRs remaining in plants and fruits after application.

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