What Are Plant Growth Regulators? PGRs Explained

If you have been growing or gardening for a while, you have more than likely heard of plant growth regulators. In fact, you might have recoiled just reading those words!

More commonly called PGRs, plant growth regulators don't have the best reputation among growers for a variety of reasons. Others however consider them essential when growing apples and other fruiting plants.

So what exactly are PGRs, and should you use them on your plants?

What are plant growth regulators?

Like the name implies, plant growth regulators do just that; regulate plant growth. Whether it's inhibiting upward growth or lateral growth, or increasing water uptake and flower density, PGRs can do a lot.

When it comes to classifications, plant growth regulators are broken into five groups: Auxins, Gibberellins, Cytokinins, Abscisic Acid, and Ethylene.

Auxins encourage the elongation of shoots, but at high concentrations they can inhibit growth of lateral buds. In addition to being used as plant growth regulators, auxins can also be herbicides.

Gibberellins promote cell elongation, shoot growth, and are involved in regulating dormancy, mainly used to increase bud size and density. Gibberellins are most commonly used in plants like apple trees and cherries.

Cytokinins promote cell division. They are involved in branching and stimulating bud initiation, and are also a common fruit thinner. In other words cytokinins increase plant flowering while killing off younger, smaller flower lower on the plant so it can focus more energy on the main flowers.

Abscisic acid controls the dormancy of buds and seeds, inhibits shoot growth and is involved in regulating water loss from plants. Ethylene promotes abscission of leaves and fruits, inhibits shoot elongation and inhibits lateral bud development.

How do PGRs work?

Like any other plant nutrient or supplement you could pick up from a grow store like Cultivate, there are supplements that contain plant growth regulators. They can be used as part of your nutrient regiment like any other product.

When using plant growth regulators, growers will typically notice an increase in plant size and buds. The buds will typically be more dense, which increases yields in terms of weight.

However it isn't all good with PGRs.

One of the most common side effects of plant growth regulators, specifically in cannabis, is the reduction of terpene and even THC content. This is why for those who grow with PGRs, quantity is typically more important than quality.

The biggest complaint against plant growth regulators is the potential health impacts when consumed.

The dangers of plant growth regulators

In cannabis cultivation specifically, there are a few PGR products that have gained popularity among growers trying to boost yields.

Paclobutrazol is a plant growth retardant that functions as a gibberellic acid antagonist. More importantly, it hinders the ability of cells to elongate. This results in cells that pack tightly for increased density and weight in the buds.

However paclobutrazol also reduces the ability of the plant to produce THC and terpenes. Last but certainly not least, when smoked, paclobutrazol breaks down into nitrosamines, the most carcinogenic compound found in cigarettes.

Daminozide was actually banned in the US in 1999 for use in consumable plants due to studies finding it carcinogenic to humans. However it increases yields by slowing the growth of leaves and stems, and instead making the plant focus on flower production. It is listed as a potential human carcinogen by the EPA.

Chlormequat chloride helps produce thicker stems and shorter plants, slowing down plant growth to encourage flowering. Growers like this PGR specifically for indoor growing because it helps produce shorter, bushier plants.

There is currently no evidence that chloremequat chloride is carcinogenic, however there have been several documented cases of organ damage along with skin and eye irritation among people who ingested it in large amounts.

The truth about PGRs

The reality of plant growth regulators is that they aren't all bad. Despite the dangerous products some growers choose to use (which we do not sell), other growers may be using PGRs without even knowing it.

This is because the term itself is way too broad. In fact, one could make the argument that using any sort of plant nutrient or supplement is technically regulating plant growth.

Certain nutrient products and supplements provide micro and macronutrients that can increase nutrient uptake, plant growth, yields, and many of the other benefits provided by PGRs, just without the proven dangers. One such example would be a mono-silicic acid product such as Power Si.

While silica itself is natural, it can take a long time for your plants to start taking it up through the roots. Power Si uses a synthetically created mono-silicic acid that makes the silica immediately available to your plants.

Power Si helps your plants build stronger cell walls and decrease susceptibility to various diseases, resulting in stronger plants and thicker stems.

Another example is Regalia, a concentrated fungicide which contains triacontanol, a natural plant growth regulator. While used mainly for the purpose of fungi mitigation, triacontanol has been shown to be a growth stimulator as well. However triacontanol can also be made synthetically.

Long story short, plant growth regulators can be beneficial to your plants, but not all PGRs are made equal. If you truly want to incorporate them into your regiment, we encourage as much research as possible before buying any product that contains a plant growth regulator.