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What Are Growth Regulators?

July 11, 2022

Growth regulators are a group of chemicals used to modify the various growth processes in plants. These chemicals help with many issues in a plant’s lifecycle, including suppressing vegetative growth and stimulating flowering, controlling plant height, enhancing plant branching, and enabling plants to flower during short-day conditions (during late fall and winter). The chemicals used can be found inside plants already but are sometimes modified to improve or lower their efficiency and modify specific processes.

Plant growth regulators are sometimes referred to as plant hormones because the chemicals act similarly to human hormones. Hormones are chemical messengers that affect your body’s growth, metabolism, and more, the same role that regulators play for plants. Regulators are absorbed by plants via roots, foliage, or by absorption into sapwood and “tell” the plant when it is time for them to grow, flower, or enter a state of dormancy. These chemicals are slow-acting and can take weeks to affect a plant.

While growth regulators can be used to prevent plants or trees from growing, these hormones differ from herbicides. Herbicides quickly kill all the vegetation with which the substances come in contact. These regulators limit the number of nutrients a plant uses, so the plant grows slowly.

Types of Growth Regulators

Plant growth regulators can be broken down into two main types, with specific chemicals falling under one or the other:

  • Promoters enhance and stimulate cell division, plant cell enlargement, flowering, fruiting, and seed formation.
  • Inhibitors prevent growth and promote dormancy and abscission (shedding) in plants.

Examples of promoters include auxins, gibberellins, and cytokinins. An example of an inhibitor is abscisic acid. Each of these growth regulators affects specific processes within plants.


Auxins are hormones found in shoot and root tips that promote cell division and stem and root growth. This chemical is used to help stimulate cell elongation by increasing cell walls, thus helping promote the plant’s stem growth. Auxins can also drastically affect plant orientation by promoting cell division to one side of the plant in response to sunlight and gravity. Plants grow in the direction necessary to absorb the most sunlight possible, so if sunlight only shines on the western side of a plant, auxin will collect on the shady eastern side to promote growth.

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Gibberellins affect many aspects and processes within a plant, such as germination, flowering, and flower development. One of the uses of gibberellins in plant health care is growth and germination control. Low hormone concentrations can increase the speed of germination and stimulate cell elongation, so plants grow taller.


Like auxins, cytokinins are chemicals that promote cell division and the formation of new leaves. Generally, cytokinins help initiate flower budding and encourage lateral growth so that a plant becomes “bushier,” or more expansive in size. In addition, if a plant has increased absorption of water and other minerals, then cytokinins can help stimulate the metabolism of young shoot cells, encouraging growth.

Abscisic Acid

Unlike the plant growth regulators mentioned above, abscisic acid is an inhibitor, slowing down growth, metabolism, and seed germination. In addition, abscisic acid helps regulate dormancy and shedding, particularly as a response to environmental conditions and stresses, such as droughts or extreme temperatures. The chemical also plays a vital role in increasing stress tolerance and generally improving a plant’s ability to respond to stress.


While ethylene can inhibit plant growth, this chemical is sometimes used as a promoter. Like abscisic acid, ethylene promotes leaf and flower shedding but can also be used to break the dormancy of seeds and promote flower bloom.

The Importance of Growth Regulators

As mentioned above, each of these plant growth regulators affects different aspects of plant growth and development, and each is needed in different amounts based on the conditions and issues a plant faces. For example, if a plant is too short, a certified arborist or plant health care expert can provide concentrations of gibberellins to promote growth and help make the plant taller. Likewise, if a flower needs help blooming, a plant health care specialist can use chemicals such as cytokinins or ethylene to encourage blooming. All of these hormones and chemicals can be used to help plants grow in a particular way while maintaining the plant’s overall health and biology.

Contact Burkholder PHC for Plant Care Services

If you want to keep your plants and trees healthy and vibrant, contact Burkholder PHC. We offer many plant health care services, such as plant growth regulators, pest control, and soil care. In addition, our team of specialists has years of experience maintaining landscapes in the Main Line area. For more information about our services, request a free consultation today.