Hemp THC Limits: What Happens If a Hemp Crop Tests Hot for Tetrahydrocannabinol?

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Among the issues that can cause hemp crop failure—floods and droughts, pests and disease—testing “hot” for THC levels is its own headache. The hemp THC limits set by the federal government mandate that plants cannot have more than 0.3% tetrahydrocannabinol (THC) by dry weight. 

This threshold remains a bone of contention among hemp-farming stakeholders, from producers and advocates to regulators and federal officials, and even members of Congress. Of course, the overwhelming majority of hemp farmers have no intention of growing plants illicitly to get people high. They’re growing hemp for its fiber, as a food source, or for the production of cannabidiol (CBD). 

Under interim draft rules for hemp production established by the U.S. Department of Agriculture, crop samples must be gathered and tested within 15 days of scheduled harvest, and crops testing in excess of 0.3% THC must be destroyed. 

After initial pushback about the 0.3% limit, federal officials created a little wiggle room: While crops testing between 0.3% and 0.5% THC must still be destroyed, the producer won’t be criminally liable as long as the crop didn’t exceed 0.5% THC.  

So, what happens if a hemp crop tests hot for THC? When’s the best time to start testing hemp? And what’s behind the 0.3% limit, anyway?

How to Test Hemp for THC 

As U.S. hemp production has ramped up, researchers and agronomists are in catch-up mode to determine exactly what causes a hemp crop to go hot, since cannabis research has been limited by federal prohibition for decades. 

The current understanding of hemp cannabinoid production is that while genetics play a pivotal role, cannabinoids such as THC and CBD can increase significantly toward the tail end of the plant’s life cycle. And environmental factors are believed to play a role in cannabinoid production as well. 

With all of these factors and uncertainties in play, it would behoove hemp producers to conduct informal testing, aka unofficial testing, regularly in the weeks running up to the planned harvest date.

When to Start Testing Hemp for THC Potency 

It’s smart to be prepared and stay flexible during the flowering stage, in case harvest dates need to be moved up if plants exhibit an upward trend in THC. And the more data a producer has on when a cultivar starts to spike in cannabinoids, the better informed their future decision making will be. 

Producers can test plants on their own with a “home kit.” However, given the high levels of inaccuracy inherent in these tests, we cannot recommend using them, especially if producers are doing so in order to determine whether or not their cannabis is compliant with USDA regulations. They can also send samples to a private lab, or utilize the services of a lab that is state-licensed for cannabis and hemp testing. 

However, when it comes to meeting the official testing requirements for USDA compliance, only the results from a licensed testing lab such as Trichome Analytical that is also registered with the U.S. Drug Enforcement Administration will be accepted. 

For this reason, at Trichome Analytical we urge producers to work with a DEA-registered lab from the start, particularly for those who are new to growing hemp. This ensures that producers are familiar with the lab’s protocols and procedures well ahead of harvest. During one of the busiest times of year for a hemp farmer, scrambling to obtain compliant test results in a limited time frame is the last thing you want to be worrying about.  

Recommendations vary on optimal testing schedules. For example, a Colorado-based hemp seed producer suggests weekly testing, starting in the first week of flowering, and potentially more frequent testing as THC levels rise. 

Valuable Data on Hemp THC levels

A February 2020 report by news service Stateline highlights the need for more data on hemp cultivation: “The bottom line is, we don’t really have good, solid data yet to say, ‘Do this’ or ‘Don’t do this’ to try to avoid having a noncompliant level,” said Bob Pearce, an extension professor in the plant and soil sciences department at the University of Kentucky in Lexington. 

For producers hesitant about the pre-harvest costs of frequent testing, consider the consequences of not having necessary information about a crop’s cannabinoid content before the official testing happens: the producer’s hemp-growing license is jeopardized; the cost of destruction is passed along to the producer; there are the additional costs, resources and time spent growing the crop itself; and the producer has missed out on valuable data that could inform future seasons.   

While producers can pay to retest a “hot” hemp crop once the official testing period has been initiated, it’s risky to play those odds at this late stage.

Because it’s still early days for widespread U.S. hemp production, and the USDA’s final rules may still change based on public comment after the 2020 harvest season, the more information and data that stakeholders can assemble on hemp THC levels, the better.     

The History Behind the 0.3% Hemp THC Level

Here’s the backstory on why the federal government treats hemp and marijuana differently, even though they’re classified as the same genus (Cannabis) and species. 

Hemp agronomy had a rich history as a crop produced by the first colonists and early Americans, but hemp was waylaid by the Marihuana Tax Act of 1937 amid a push to ban cannabis consumption. The tax made hemp farming less appealing than other commodity crops.  

According to the nonprofit Project CBD, the 0.3% THC figure can be traced to a 1976 taxonomic report written by two Canadian plant scientists who didn’t intend for the figure to be a legal definition. However, in later court battles about hemp foods, the figure gained precedence.     

When Congress passed the 2018 Farm Bill that legalized hemp production nationwide, the hemp THC limit of 0.3% by dry weight was prominently noted. As hemp has moved into the mainstream, this shift has had its fair share of growing pains—and the contentious hemp THC limits are often called out, even by U.S. Congress members and federal agency officials.

Meanwhile, states, territories and tribes continue to develop their own regulatory frameworks that require USDA approval. You can learn more about the status of your state’s hemp plans here.

Click here to learn more about Trichome Analytical’s testing services for hemp THC potency, pesticides, contaminants and more.