Harvesting Hemp Early Maximizes CBD Obtaining, Study Says

Hemp growers should harvest their plants before they reach full seed maturity if they want to maximize the amount of CBD that can be extracted, suggests one new study published in Royal Society Open Science. 

According to the latest investigations by scientists from york university, in the United Kingdom, and the Khon Kaen University, in Thailand, global levels of cannabinoids, including CBD, peak in the popular hemp variety Finola about nine weeks after sowing, before they begin to decline. However, the best CBD:THC ratios for extraction were achieved in the flowering stage, just eight weeks after sowing. 

These results demonstrate the importance of studying the evolution of the metabolite in hemp plants over time, say the researchers, especially given the growing demand for CBD that is being fueled by a multi-billion industry of CBD products. 

Harvest early to maximize CBD production 
To carry out this study, the researchers planted 160 seeds of the Finola which produced a total of 90 female hemp plants that could be studied. These plants were then harvested during one of four potential harvest windows:  

1. During the vegetative phase, four weeks after sowing;  

1. During the flowering phase, eight weeks after sowing; 

1. After the flowering phase is complete, nine weeks after sowing; 

1. Seed maturity stage, eleven weeks after sowing. 

During harvest, the plants were divided into their leaves, stems and inflorescences (flowers), with each batch of plant material prepared separately for testing. The tests were done using a Sohxlet extraction technique to extract the crude resin product, which was pre-weighed before being analyzed using a high temperature gas chromatography (HTGC) method. 

Comparing the yields for each part of the plant at each stage of the harvest cycle, the researchers found that the gross yield of the extract was highest for stems in the first established harvest window, but peaked for leaves and flowers in the fourth window. of harvest. 

Composition analysis revealed that the greatest number of cannabinoids were found in plant flower extracts, while the leaf extract was largely made up of wax esters and steroid compounds. In flowers, cannabinoid content increased over time until reaching a peak in the third harvest window, which decreased slightly in the fourth harvest window. The highest amount of CBD was also found in the third harvest window. 

"Initially, as hemp grows, cannabinoid levels are low until the plant reaches flowering," study author Andrew Hunt told Newsweek. "The cannabinoid content then decreases until seed maturity is reached."  

Early harvest may limit THC development
Maximum levels of CBD are not the only important compositional factor to study in hemp maturation; equally important are the plant's THC levels. 

“In the US [as well as Europe which has already agreed to raise the limits], the legal limit for THC concentration cannot exceed 0,3% on a dry weight basis in any part of the plant, seeds or extracts,” explained Hunt. 

A plant that produces high amounts of CBD and THC will need extensive post-harvest processing to remove that THC and create a CBD isolate, distillate, or other product that can be sold. But having a plant that naturally contains a lot of CBD and low levels of THC will make CBD isolation and purification much easier. 

The researchers found that while total amounts of CBD peaked in the third harvest window in this study, the most favorable CBD:THC ratio was seen in the second harvest window, as THC levels were significantly lower. here than during the third harvest window. 

“The highest proportion of cannabidiol was extracted from the flowers in full bloom, however a significant increase (63%) of the psychoactive banned tetrahydrocannabinol (THC) was observed at this harvest stage compared to the flowering stage where the plant begins to bloom. bloom,” Hunt said. 

"Picking the flowers after flowering would be preferable due to the high cannabidiol content and low amounts of THC." 

The researchers say this study highlights the importance of studying the variation of cannabinoids and other plant compounds in the hemp plant as it matures, in order to identify different harvest times that can maximize the plant's potential industrial value.