Balancing Plant Growth Regulators (PGR) Principles

By Rich Hamilton
Published: November 1, 2016 | Last updated: April 21, 2021 05:12:09
Key Takeaways

Plant growth regulators (PGR) have their benefits, but they also have their drawbacks that can include health concerns for people who consume what they grow. Rich Hamilton explains what plant growth regulators are, what they do and what questions consumers should be asking when purchasing them.

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Starting with the basics, PGR stands for plant growth regulators, sometimes also referred to as plant hormones. Every plant naturally produces very small amounts of hormones in order to control its normal functions such as root growth, height, node and internode growth, flowering, quantity of flowers, fruit and any other developmental growth.


Plant growth regulators are a chemical or mix of chemicals that make a plant change beyond its naturally physiological growth actions, through the cells, organs and tissues. It does this by either slowing down the rate of growth or maturation; speeding up the rate of growth or maturation; or altering the natural behavior of a plant. Note that this does not include any substances which are intended as a plant nutrient, including trace elements, plant inoculants or nutritional chemicals.

The term PGR has come to include many things, and not all of them are harmful. Some of the of major classifications of plant growth regulators are auxins, cytokinins, ethylene generators, gibberellins and growth inhibitors/retardants. Auxins elongate shoots. They are primarily used to increase growth, flower formation and to increase root mass.


Cytokinins stimulates cell division and are primarily used to increase root mass and new bud growth. Ethylene generators ripen fruit and are primarily used to ripen fruit uniformly, giving the plant consistent fruit size and weight.

Gibberellins elongates cells and stimulate cell division and are primarily used to increase fruit and flower size. Finally, grow inhibitors and retardants stop or slow down growth. They are primarily used to increase flower production by shortening the internodes, make more node sites and/or to completely stop the lateral growth of a plant.

So the big question is, are PGRs illegal? Well, no, not if they are used on ornamental plants but without going too far down the rabbit hole of what is and isn’t legal, what I can say is that some are prohibited for use on plants grown and intended for human consumption.


Good Control

PGRs are a great way to control plants. They will, if used in the right mixtures at the correct dosages, considerably improve the desired factors. PGRs can help a plant to produce more flowers and fruits and assist in producing even consistent flowers and fruits. They can help you keep plant height consistent and reduce the time it takes for a plant to produce its flowers and fruits. They can also make a plant less susceptible to fungi, diseases and pests.

PGRs can control plants in order to preserve the balance between the modern world and the natural world. By that I mean they have been used to stop growth in trees growing too high, which otherwise would have to be destroyed in order to prevent them from growing under bridges, telephone cables and in other urban locations damaging or obstructing footings, buildings and foundations.


At the other end of the scale, they can make houseplants stay manageable and become more resilient to stress and disease. PGRs are also used commonly and successfully within the retail flower business. They are used to make the flowers more appealing to the retail consumer by improving consistency in flower size and color.

We’ve covered the positive attributes, so what’s the problem? As is often the case, when something seems too good to be true, it usually is.

A Moral Choice

Most people, including hydroponics shop owners and customers, would prefer not to sell or buy products that contain PGRs, if given a choice, but most do. There are several reasons for this, the first being companies that produce the nutrients and additives do not always inform shop owners that their products contain PGRs so the shop owner is none the wiser.

On the flip side, some of the products that contain PGRs are so popular and sought after, a shop owner may find him or herself stuck with a moral choice. The owner can attempt to educate customers as much as possible on the benefits of non-PGR products but the bottom line is that they are a business, so if they don’t have the PGR products that the customer want in their store, they run the risk of losing that customer and sale to a rival.

Finally, there are those only interested in achieving the heaviest and most financially rewarding yield from the plant and are willing to overlook the health concerns related to PGRs. In reality, PGRs are out there and it is impossible to tell what plants they are in and at what levels. But this can all be taken care of if plants are flushed before harvest, right?


PGR chemicals are nearly all systemic, which means that once they are taken up into the plant, trace chemicals will always be in the plant, its flowers, fruits, roots, tissues, pollen…everything. Therefore, it follows that if you cannot be sure what levels of PGR are present in the additives you are using due to the lack of information given in the ingredients list, then you would have no idea of the level of potentially harmful PGRs in any part of your fully grown plant, including the fruit before and after harvesting.

The Right Questions

There is a lack of pretty much any regulation or regulative body on chemicals used in the hobbyist hydroponics industry. This means that most of the nutrient and additive companies don’t have state whether their product contains any PGRs, the quantities contained or specify which PGR it is.

The bad press surrounding PGRs, most notably that the majority of them are banned in most countries for use on plants and their fruits that are intended for human consumption, only adds to the desire to keep their presence in any products a secret.

You’re probably thinking that surely the nutrient companies can’t knowingly put these chemicals in their products without telling the customer. However, like antibiotics in meat or chemical ingredients in packaged foods, the simple and honest truth is yes, some of them do. Not only that, they also don’t tell us. Like anything else you consume, know what you are buying. Here are a few questions to ask your retailer or manufacturer when purchasing nutrients:

  • What PGRs, if any, are in the products they sell?
  • What will those PGRs do to the plant?
  • Should they be used on anything intended to be consumed by humans?
  • What effects will the chemicals have if the produce of the plant is consumed?

The bottom line? The next time you go to buy nutrients, ask if the product contains PGRs. Only by asking and buying better can we create a better, safer market for ourselves in the future.


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Written by Rich Hamilton | Writer, Consultant, Author of The Growers Guide

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Rich Hamilton has been in the hydroponics industry for more than 20 years, working originally as a general manager in a hydroponics retail outlet before becoming an account manager at Century Growsystems. He enjoys working on a daily basis with shop owners, manufacturers, distributors, and end users to develop premium products.

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