0.3% THC: THE MOST COMMON QUESTION
The major scientific problem (besides “we arbitrarily adopt…”) is that the widely implemented 0.3% THC concentration limit is often applied to flowering tops (where cannabinoid production is concentrated) instead of the “young, vigorous leaves of relatively mature plants” identified by Small and Cronquist. As we all know, the difference in cannabinoid content between a leaf and a flower is significant, which means current sampling protocols do not match published science. Today, we are aware that the real difference between “industrial hemp” and “marijuana” is derived from two separate genes that are tightly linked (located eight centimorgans apart on chromosome six) and fight to convert the precursor cannabinoid CBG to either THC or CBD when both genes are present.
The Detailed Answer
When THC production genes are turned “on” and CBD is turned “off,” plants are THC dominant, psychoactive, and are considered type I (recreational and medical). When both CBD and THC genes are turned “on,” plants are moderately psychoactive (as CBD lessens the psychoactivity of THC) and are considered type II (medical). When CBD production genes are turned “on” and THC is “off,” plants are considered type III (industrial hemp). When both THC and CBD production genes are “off,” plants only bioaccumulate CBG and are considered type IV (also industrial hemp). When upstream cannabinoid production precursor genes are turned off, no cannabinoids are produced (only terpenes), and the resulting plants are considered type V ("cannabinoid free," also industrial hemp).
Even with the THC genes “off,” type III and IV plants still produce a small amount of THC; the reason for this was unknown until we discovered the answer in early 2019. After tens of thousands of chemical and genetic tests (including whole genome sequencing of hundreds of plants), we now know that THC accumulation in type III and type IV varieties is due to CBCA genes, located on chromosome nine (remember: CBD and THC genes are located on chromosome six).
Figure 3. Cannabis Chromosomes
Critical Considerations for Success
As an example: a 15% plant with a 25:1 ratio would contain:
Total Cannabinoid Content
Sampling Protocol and Timing--Whose 0.3% THC Counts?
Timing of Test
- Oregon: 28 days before harvest begins
- Kentucky: 15 days before harvest is complete
- Pennsylvania: 70-80 days after planting
- Oregon: Top 8 inches of 30 plants; delta-9 only (no decarboxylation); carried out by private, nationally accredited labs.
- Kentucky: Top 20cm of 5 plants; delta-9 THC + (THCa * 0.877); carried out by Kentucky Department of Agriculture
- Pennsylvania: Terminal flowers only (top 2 inches); delta-9 THC post-decarboxylation; farmer collects sample, sends to any lab in the US
Samples were collected from 55,750 plants over 12 acres of undulating field conditions by 8 separate sampling teams following ODA’s prescribed pattern and protocol. Significant differences in price, LOQ levels (lower is better, when accurate), and gross total content were apparent. All of our samples came in well below the total 0.3% THC threshold, with the exception of Cascadia’s test (which was grossly mishandled by commingling our sample with a high THC sample after accidentally throwing both in the trash (you can't make this stuff up)--the company no longer operates in Oregon). Sampling technique (i.e. biomass selection) has the greatest influence on total cannabinoid content (both CBD and THC) and this is apparent when comparing results; for reference, the reported THC content from Green Leaf Labs, Pixis, and SC Labs are the closest to those we have received from ODA in previous compliance events with this particular variety. Not all labs test for the acidic forms of non-THC and CBD cannabinoids; at least one lab (Evio) inappropriately reported high levels of CBN instead of CBGA, while missing CBCA accumulations entirely and misreporting their actual LOQs. While this does not affect your THC compliance, it is definitely an issue that savvy growers should pay attention to, since many states place civil responsibility on farmers to select a lab with great record-keeping practices (Oregon requires growers to maintain records for at least 3 years post-harvest—always keep copies for yourself, just in case).
Figure 6 also includes imputed CBD:THC ratios derived from the test-day results. As we have previously described, these ratios represent important breeding markers for those interested in maximizing oil production, since higher ratios allow for greater CBDa in ultra-low THCa, federally compliant plants. In these tests, results ranged from 16:1 to over 56:1 amongst labs, with an average (mean) of 27.2:1. We are not surprised to find that the lab with the lowest LOQs (Pixis) produced results in agreement with this population average. This is an important finding for farmers to consider when vetting claims made by seed vendors or breeders—there is no such thing as “non-detectable THC” in CBD-rich hemp just yet, only inaccurate lab results.