Hemp Production – Keeping THC Levels Low

— Written By
Image of hemp varieties

Leo Stefanile, Margaret Bloomquist, and Zeke Overbaugh showing differences in root development of two hemp varieties.
Read the full article

Hemp Production in North Carolina is new and changing rapidly. There is a massive shortage of research-based info regarding the basic agronomic recommendations but we are making progress. Because of the great interest in hemp from our farmers, industry, community leaders, and potential consumers of hemp products I will summarize what I have learned from listening to numerous people working with this crop.

Hemp can be grown for seed, fiber, or flower (oil extracts). In 2018, North Carolina had  6133 licensed acres, 394 licensed growers, and 1.6 million square feet in licensed greenhouse space. The majority of production is focused on growing hemp for flower, primarily the CBD market. CBD, or cannabidiol, is one of over 100 cannabinoids identified in hemp plants. Another cannabinoid is THC, tetrahydrocannabinol, which is the psychoactive ingredient in cannabis that gives a ‘high’ effect. The amount of THC in a cannabis plant determines whether it is hemp or whether it is marijuana. If the THC content is 0.3% or less, it is hemp. If the THC content is greater than 0.3% it is marijuana.

Image of hemp flower

Female hemp flower. Most (but not all) hemp cultivars are dioecious, meaning male and female flowers are found on separate plants. Hemp growers interested in CBD production want female plants. Photo by Debbie Roos. See full article here.

Licensed growers of hemp in NC are required to contact the North Carolina Department of Agriculture & Consumer Services (NCDA&CS) at the initiation of flowering (industrialhemprequests@ncda.gov). Growers must report when plants are flowering and, thus, are ready to be tested for THC. Someone from NCDA&CS will visit the site and sample hemp 3-5 weeks into flowering. They will take the top 3-5 inches of the plant (NCDA&CS is sensitive to the value of biomass and they are working to minimize the total amount of biomass removed) and if you have multiple varieties you will need multiple tests. The grower must pay for all testing ($59 for the first test). If the level of THC is above 0.3% you will have two options – destroy your crop or pay for a re-test of the THC ($149 for the re-test).

Growers need to be aware that plant stresses (drought, flooding, excessive nutrients, not enough nutrients, heat, cold, etc) can result in THC spikes. According to Paul Adams with theNCDA&CS, in 2017, the NCDA&CS processed 135 hemp samples and 14 came back above 0.3% THC. In 2018 they processed 400 hemp samples and 38 came back above 0.3% THC. About 10% of hemp fields are ‘going hot’ – lingo used to describe a THC spike. This is a serious risk to hemp producers and there is currently no crop insurance to mitigate this risk.

We don’t have solid data on the causes of THC spikes but here are some considerations. While excess nitrogen is often blamed for THC spikes, Dr. Angela Post, NC State University Small Grains Specialist, disagrees with this. In one research trial that Dr. Post conducted, nitrogen was applied at rates of 50, 100, 150, 200, 250, and 300 lbs per acre. While there was no advantage at putting out more than 100 lbs of nitrogen per acre there was no spike in THC. In fact, from just this first year of preliminary data, Dr. Post did not see any relationship between nitrogen and THC or CBD. In fact, Dr. Post wonders if nitrogen deficiencies could result in plant stress, thus causing a THC spike. From just this first year of data the nitrogen recommendation would be 100 lbs of N per acre. However, Dr. Edminsten cautions that this is just one season of data. If he were growing hemp right now he would lean towards a higher nitrogen rate (120 lb/N per acre).

Altitude or cooler weather at certain stages of plant development may affect THC. Again, there is no multi-year, replicated research information for NC hemp, but a variety trial of hemp was conducted at the Piedmont Research Station (elevation 703 feet) near Salisbury and the Mills River Research Station (elevation 2,069 feet) near Asheville. The same varieties were planted at both locations. None of the varieties had high levels of THC in the Piedmont location while all of the varieties tested ‘hot’ in the mountains!

Certainly, variety selection will play a role in THC content of the hemp varieties. We are still gathering information for growers regarding variety performance in NC but there is a listing of how some varieties have performed in Kentucky, including which of those varieties are of concern for THC spikes.

Take a look at this article for more information on prices for hemp floral biomass: Hemp Production: Market Opportunities and Risk

The information regarding hemp is changing quickly so keep visiting these resources and stay tuned.

Industrial Hemp Portal with NC State

NCDA&CS – Hemp Pilot Program in NC

Growing Small Farms – Hemp Short Course

Business of Hemp Webinar