A Guide to PGRs in the Grow Room

Tara | April 13, 2022
A Guide to PGRs in the Grow Room
What are PGRs?

PGRs, or plant growth regulators, are synthesised chemicals that mimic the natural hormones of plants. PGRs can promote certain characteristics by triggering physiological responses. They are normally used to promote larger, denser flowers and shorter, stockier plants. Growers often refer to them as ‘steroids for plants’ and they are used frequently in the Australian market.

PGRs are generally classified by one of two functions:

  1. Plant growth boosters which promote growth through cell division, boosting flower production and size and stimulating root and and shoot development .
  2. Plant growth inhibitors which promote dormancy and abscission (the natural loss of ripe fruit and dead leaves). Inhibitor PGRs enable indoor growers to keep their plants small and dense, directing energy to producing larger and tighter flowers.

The most commonly used PGRs in Australia are:

  • Paclobutrazol (PBZ)
  • Daminozide
  • Chlormequat Chloride

All three are plant growth inhibitors that increase the density of flowers by limiting growth in other areas of the plant. For example, stem elongation may be stunted in order to direct energy toward flowering.

Are PGRs bad for you?

PGRs contain chemicals that are not approved for human consumption. In high concentrations, PGRs can leave traces present in the flowers which will eventually be consumed. Combustion transforms these traces into active chemicals that may be dangerous in unregulated concentrations. PBZ turns into molecules called nitrosamines which are present in cigarettes, and associated with cancer, liver damage and male infertility. Because PGRs are not approved for human consumption, they should not be smoked or ingested.

The PGR Daminozide is also classified as a “probable human carcinogen”. It is carcingoenic in high doses, and is banned for use in many agricultural settings.

While PGRs are not banned by the Australian government, they are heavily regulated. Products that include PGRs are required to register with the Australian Pesticides and Veterinary Medicines Authority.

Do PGRs effect the quality of your plants?

PGRs can limit the production of trichomes, terpenes and cannabanoids resulting in a less potent and flavourful fruit or flower.

Are there natural PGRs?

Yes! Natural or organic PGRs provide plants with an additional supply of auxins and cytokinins. Examples of natural PGRs include seaweed, kelp extract, bat guano extract and alfalfa extract found in products such as BAC Organic Grow & Bloom, BAC Organic PK Booster, NTS Tri-Kelp, and Nature’s Own Super Bloom Guano.

Signs of PGRs

Signs that a flower has been grown with PGRs:

  • Rock hard, dense, heavy flowers
  • Red brown colour
  • Excessive amount of red hairs (pistils)
  • Lack of crystals found on the leaf and flowers
  • Less cannabanoids that will effect the ‘high’
  • Harsh chemical taste
  • A fast-acting chemical ‘high’ that may cause lethargy and headaches

See Plant Hormones 101 to learn more.

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