A survey of 1,722 cannabis growers found 44% used chemical fertilizers, with hydroponic growing as the key predictor | Research

The takeaway

A survey of 1,722 small-scale cannabis growers in Australia, Denmark, and the UK found that 44% used chemical fertilizers, supplements, or insecticides, with hydroponic growing as the only significant predictor of chemical use, and labeling issues made it difficult to determine which products contained harmful chemicals.

Cannabis regulators and public health officials; home growers concerned about product safety; researchers studying cannabis contaminants.

44% of growers used chemicals, with PGRs potentially hidden in unlabeled products

What the researchers found

Researchers surveyed 1,722 current and recent small-scale recreational cannabis growers across three countries about their growing practices.

Overall, 44% reported using any chemical fertilizers, supplements, or insecticides.

Logistic regression found that hydroponic growing was the only significant predictor of chemical use. Other factors like country, experience level, or scale did not independently predict chemical use.

A major concern was plant growth regulators (PGRs), which limit plant size and stimulate bud production. Many PGRs have been banned from food crops but are found unlisted in cannabis growing nutrients sold online and in hydroponic stores.

The researchers found that product labeling and uncertainty about constituents made it difficult for both growers and researchers to determine which products contained PGRs or other harmful chemicals.

Why it matters

As legal cannabis markets grow, consumer safety depends on understanding what chemicals end up in the final product. This study reveals that even small-scale growers commonly use chemicals, and the products available to them are poorly labeled, creating a hidden health risk for consumers.

The numbers in context

1,722 growers surveyed across 3 countries. 44% used chemical fertilizers, supplements, or insecticides. Hydroponic growing was the sole significant predictor of chemical use.

How the study worked

Web survey of 1,722 cannabis growers in Australia, Denmark, and the UK. Logistic regression to identify predictors of chemical use. Assessment of product labeling and constituent transparency.

What this study cannot tell us

Self-selected web survey sample may not represent all cannabis growers. Self-reported chemical use may underestimate actual use. Product constituent analysis was limited by poor labeling. Three-country sample may not generalize globally.

How to read the evidence

Moderate. Large multi-country survey, but self-selected sample and self-reported data introduce potential bias.

When this study was published

Published in 2018. Cannabis cultivation regulation has evolved in legal markets, though concerns about chemical contaminants persist.

The bigger picture

Legal cannabis markets have begun requiring pesticide and contaminant testing, but unregulated home-growing and gray-market production continue without oversight. The PGR problem is particularly concerning because these chemicals can be present in products marketed specifically to cannabis growers without appearing on labels.

Questions still open

What health effects do PGR residues have on cannabis consumers? Would mandatory labeling of cannabis growing products reduce harmful chemical use? How does chemical use differ between legal commercial operations and home growers?

Common questions

What are plant growth regulators and why are they concerning?

Plant growth regulators (PGRs) are chemicals that control plant growth patterns. In cannabis cultivation, they are used to produce denser buds. Many PGRs have been banned from food crops due to health concerns including potential carcinogenicity. They can be present in cannabis growing products without being listed on labels.

Does this only apply to illegal growers?

The study surveyed small-scale recreational growers, but the chemical products they use are the same ones available at hydroponic stores that serve both legal and illegal growers. Legal commercial operations are typically subject to testing requirements, but home growers and gray-market producers generally are not.

Read the original research

Growing practices and the use of potentially harmful chemical additives among a sample of small-scale cannabis growers in three countries.

Drug and alcohol dependence, 192, 250-256

View on PubMed ↗Publisher’s paper ↗

Citation

Lenton, Simon; Frank, Vibeke A; Barratt, Monica J; Potter, Gary R; Decorte, Tom. (2018). Growing practices and the use of potentially harmful chemical additives among a sample of small-scale cannabis growers in three countries.. Drug and alcohol dependence, 192, 250-256. https://doi.org/10.1016/j.drugalcdep.2018.07.040