3 Tips for Increasing Secondary Metabolites in Cannabis Cultivars

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Why running careful experiments is key when testing how to boost cannabinoids, terpenoids and other secondary metabolites.

Photo by Holly Fulmer Sullivan/Dr. Dank

Galenas, an Akron-based Level II cultivator in Ohio’s medical cannabis program, operates in a state-of-the-art facility with a highly controllable environment. We’ve made many improvements toward our goal to produce the highest-quality cannabis in Ohio.

Now we are in a place where we can run experiments, and one aspect we are tinkering with is a technique to increase secondary metabolites (e.g., cannabinoids, terpenoids) in our cultivars. Here’s what we’ve learned in our early research and the studies that inspired the tests.

1. Consider growth-promoting rhizobacteria to increase plant growth and metabolite production.

A study published in June 2018, titled, “Plant growth-promoting rhizobacteria (PGPR) in Cannabis sativa ‘Finola’ cultivation: An alternative fertilization strategy to improve plant growth and quality characteristics,” has shown that plant growth-promoting rhizobacteria, or PGPRs (not to be confused with plant growth regulators (PGRs)), had positive effects on the cannabinoid content of a low-psychoactive industrial hemp cultivar. Two different PGPR inoculum concentrations demonstrated that combinations of several species of rhizobacteria effectively enhanced plant growth and development, while also increasing the accumulation of secondary metabolites. This is promising research for organic growers who work to protect and augment microbial diversity in their substrates.

2. Avoid excessive organic fertilization during flowering.

Dr. Deron Caplan, director of research and development for The Flowr Corporation and formerly with the University of Guelph, published several peer-reviewed articles on cannabis production that have relevant information for cultivators interested in enhancing secondary metabolites. One, titled, “Optimal rate of organic fertilizer during the flowering stage for cannabis grown in two coir-based substances,” describes an experiment where researchers tested a medical cannabis strain with five rates of organic fertilizer, and found that increasing the fertilizer rate led to improved growth and larger yield, but also caused a dilution of THC, THCa and CBGa. The study concluded that to maximize secondary metabolite concentrations, applying excessive organic fertilizer should be avoided during flowering.

3. Test controlled drought stress.

In another study by Dr. Caplan, titled, “Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress,” one controlled application of drought stress showed increased secondary metabolite concentrations. To evaluate the effect of drought on cannabis, the researchers withheld fertigation during week 7 in the flowering stage, when cannabinoid concentrations were peaking. They kept this up until plants reached the drought-stress threshold, which in this specific cultivar correlated with wilt, at 11 days without fertigation. They found that upon harvest, the drought-stressed plants had increased concentrations of THCa by 12% and CBDa by 13% compared to the control.

Coming from mainstream agriculture, I noticed this in my work with various culinary herbs that produce essential oils and will be testing this further in cannabis at Galenas. For those who are interested in experimenting themselves, keep in mind that certain cultivars will sustain permanent damage by the time they show wilt, so this is not always a safe reference point. Plants grown indoors already experience significant stress from an artificial environment, often combined with insect and/or disease pressure, so when inducing any type of stress, keep all other variables optimal. Be very cautious when playing with stress or running any experiments. Start with small tests and scale up slowly if results are positive. And, of course, make sure you are accurately recording and interpreting all data.

Christine DeJesus is director of cultivation at Galenas.