What is PGR Weed and How to Spot It

Cannabis plants growing indoors under artificial light and bottles filled with chemicals

PGR weed is cannabis that has been artificially enhanced with plant growth regulators. Plants treated with these chemicals have an unusual appearance of lower quality and are potentially hazardous to your health. However, there are ways you can learn to recognise it and distinguish it from natural genetics.

Cannabis showcases an incredible diversity, with some strains displaying vibrant hues such as blood reds and purples, while others feature an exceptional abundance of pistils or resin glands. At times, to cannabis connoisseurs, certain buds may appear unnatural, exhibiting an unusually dense texture and an abundance of orange pistils. While such characteristics can arise naturally, the encountered weed may contain artificial PGRs. But what is PGR weed, and how can we avoid it?

What is PGR weed?

Stacked dried cannabis buds against the white surface

PGR, or plant growth regulators, refers to hormonal chemicals in plants, regulating their growth. In cannabis cultivation, the use of artificial PGRs enhances bud density and can substantially augment yields. However, it is important to note that the application of PGRs in horticulture and agriculture is subject to strict regulations in many countries, and its use in conjunction with cannabis cultivation is deemed highly problematic.

Black market growers often choose to apply PGR to their cannabis plants to gain more sizeable yields and higher profits. The result? Enormous, densely-packed buds that seem tempting at the first glance. However, this chemically modified marijuana exhibits lower quality when compared to its organic or natural cannabis counterparts. It might look impressive to the untrained eye, but PGR weed has less beneficial compounds and more artificial additives, which are potentially harmful.

What are plant growth regulators?

Plant growth regulators describe various chemical compounds that affect plant growth on a molecular level. These compounds regulate all kinds of biological processes regarding physiology, growth and behaviour. In plants, they act as a communication system, telling the organs when to grow taller, make more leaves, or produce flowers, fruits or seeds.

A person holding a bottle with written “Plant Grow Regulators” and cannabis plants

When they occur naturally, we call them plant hormones or phytohormones. However, when mentioning their artificially synthesised equivalents, the term plant growth regulators, or PGR is commonly used. So, let’s explore them both!

Natural plant hormones

Natural plant growth regulators, or plant hormones, are produced by all plants, animals, and humans. When it comes to cannabis, these minuscule natural compounds have a significant influence on growth development, including its vigour, posture and bud formation.

Their effects within a plant are complex and sometimes even seem contradicting, which is why they are the subject of continuous research. For example, the naturally produced PGR indole acetic acid in low amounts can stimulate root growth while inhibiting root growth in higher concentrations.

Artificial plant hormones

For decades, PGRs have been used in agriculture and horticulture due to their distinct traits and characteristics, offering a wide range of options to choose from. For example, they are instrumental in producing more colourful flowers, maintaining a dense grass cover on sports fields, and are widely used to enhance the quality of fresh produce. However, throughout the USA and Europe, the use of PGRs in food crops is strictly regulated, and are classified as pesticides.

While beneficial in specific contexts, certain PGRs have proven detrimental and unsafe for human health. Regrettably, some growers persist in considering it a viable option for cannabis cultivation.

How do they work?

The PGRs applied in cannabis cultivation are all inhibitors of the hormone gibberellin, which promotes stem growth. When such inhibitors are introduced to cannabis plants, it leads to a more compact plant structure with shorter internodal spacing and more vigorous root formation. This means plants treated with PGRs can effectively produce more bud sites along the central mainstem. which results in a more substantial harvests, compared to cannabis grown without PGR.

This does, however, not mean that PGR weed has the same concentration of beneficial compounds like regular cannabis. The synthetic hormones are only stimulating certain parts of the plant. They are not responsible for the creation of more cannabinoids such as THC, terpenes, or flavonoids. PGR enhanced buds might look like they have high potency, but in fact this is more show than substance.

So let us check out the three main PGRs for cannabis you should be aware of:

1. Daminozide

A chemical formula of daminozide against the white background

Daminozide, also known as Alar, allows the plant to redirect more energy towards the development of flowers, by slowing down overall plant growth. However, daminozide has also been found to hinder cannabinoid production. It was previously used to control growth and enhance storage quality of apples, but in 1989, the U.S. Environmental Protection Agency proposed banning it due to elevated health concerns associated with its consumption.

2. Paclobutrazol

A chemical formula of paclobutrazol against the white background

Paclobutrazol, or PBZ, leads to shorter, sturdier cannabis plants. It promotes early flowering and increased seed production. However, the downside of paclobutrazol is its impact on terpenes and trichomes, affecting cannabis aroma, flavour, and potency. While it can yield heavier flowers, it therefore reduces their quality. Beyond cannabis, PBZ finds use in agriculture and arboriculture, enhancing drought resistance and foliage health.

3. Chlormequat Chloride

A chemical formula of chlormequat chloride against the white background

Chlormequat chloride is known to contribute to denser flower clusters and accelerate the plant’s transition to the flowering stage. Its property to lead to robust, thicker stalks, is a trait beneficial for harvesting ornamental flowers and cereal crops. However, it is also known to cause skin and eye irritation, and excessive use can even lead to organ damage. Despite these risks, chlormequat chloride is still used in black market cannabis cultivation to increase profit margins.

What does PGR weed look like?

A cannabis bud treated with PGR against the black background

PGR weed is not always easy to distinguish from regular cannabis. Even with lots of cannabis experience, it can be challenging to recognise PGR weed. Here are the five most striking telltale signs you should know to recognise it:

1. Dense

PGR buds are much denser than regular buds. They tend to look more like tough nuggets. While some indica genetics like Big Bud and Super Skunk are famous for having naturally dense buds, PGR weed can bring this to an extreme, without delivering on the quality. PGR buds can be extremely compact and heavier than what you might be used to.

2. Tough texture

Cannabis treated with PGR not only appears dense, but has a hard texture and feels tough, almost rock. Another tell that you night be holding weed treated with PGR is if your buds feel unnaturally squishy, almost like a sponge. When cultivating cannabis without synthetic hormones, a spongy texture might be a sign of botrytis, a common fungus infection.

3. Lack of aromas

One of the most reliable methods to distinguish natural cannabis or PGR weed is by smelling it. PGR weed has a lot less aroma and sometimes even smells like chemicals. This is because cannabis treated with growth hormones have a smaller concentration of terpenes, which are responsible for cannabis’ remarkable fragrances.

4. Covered in pistils

Another visual clue to identify PGR weed an abundance of orange pistils. These small, hair-like structures on the buds serve the primary function of collecting pollen from male plants. While orange pistils are a natural part of cannabis anatomy, they are often unnaturally vibrant and more abundant in PGR weed.

5. Rounded appearance

While well-trimmed flower buds can be a sign of high-quality treatment, PGR buds often have almost no outgrowths in their flowers, giving them an unnaturally round appearance.

What’s the difference between PGR weed and natural cannabis?

PGRs are highly problematic when it comes to cannabis, primarily when they are used without any regulation. Often, plants are sprayed with these chemicals throughout the cultivation cycle, while the nutrient water is also loaded with PGRs. This results in harmful residual chemicals building up in the medium. Considerate growers may flush the plant to remove any unwanted residues, but this is not likely, if you’re growing PGR weed. 

A person holding two cannabis buds, one grown naturally and one treated with PGR

It is perfectly fine for growers to use organic fertilisers and hormones to optimise their harvests. PGRs like paclobutrazol, daminozide, and chlormequat chloride, however, are almost exclusively used to maximise profits without improving the quality. Cannabis treated with these fertilisers have fewer cannabinoids, terpenes and flavonoids compared to natural, organically grown cannabis.

Due to their association with increased health risks, PGRs are subject to strict regulations and banned in several countries for use on fresh produce and other food products.

Cannabis enthusiasts should steer clear of PGRs

A person with black gloves and a magnifying glass inspecting a dried cannabis bud

In summary, plant growth regulators (PGRs), while useful in some agricultural contexts, are highly problematic in cannabis cultivation. These artificial plant hormones lead to plants with unusually high numbers of flowers while lowering concentrations of beneficial cannabinoids, terpenes and flavonoids. Residues of these chemicals might even be hazardous for your health, and it’s wise to be cautious of these products.

Take note of the indicators highlighted in the article and steer clear of buds displaying an unusual concentration of these traits. While not everyone has the space to grow their own cannabis, it can be a great solution to avoid any cannabis that is grown irregularly.

  • Disclaimer:
    Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.

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    Sensi Seeds

    The Sensi Seeds Editorial team has been built throughout our more than 30 years of existence. Our writers and editors include botanists, medical and legal experts as well as renown activists the world over including Lester Grinspoon, Micha Knodt, Robert Connell Clarke, Maurice Veldman, Sebastian Maríncolo, James Burton and Seshata.
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