Since the Farm Bill has legalized growing hemp, producers and researchers are working to learn about the most effective harvesting methods. Penn State University Extension horticulture educator Krystal Snyder recently presented on the topic for a webinar.
She listed a few terms important for the hemp grower to know at harvest time: cola, the entire bud and surrounding plant materials; bucking, harvesting machine that removes the buds from the stems prior to trimming; and terpenese, aromatic oils that give hemp its smell.
Knowing when to harvest is important because “at a certain time, both CBD and THC will climb,” Snyder said, as harvest time approaches. CBD is the extract from the plant that’s now legal to sell as a supplement. THC is the component inherent to plants in the cannabis family, including both hemp and marijuana. Hemp plants must be below 0.3% THC to remain legal. Otherwise, the farmer’s entire crop must be destroyed. THC naturally occurs at higher rates in marijuana, which is why it causes psychoactive effects.
Snyder said to look for visual clues as to the proper harvest time, including when the trichomes on the hemp bud shift from white to milky white and then to amber.
Weather may also influence harvest time.
“If you see a big storm, you may want to think about that,” Snyder said.
A strong storm could cause large biomass losses.
Smaller producers tend to hand harvest by either cutting the whole plants in the field or cutting the side stems. Equipment for harvesting usually cuts the entire plant and then it’s placed on a wagon or truck.
“There’s no right or wrong way, but how you’re equipped to do it,” Snyder said.
As for bucking and trimming, Snyder said there’s two schools of thought: pre-drying or after drying. With pre-drying, farmers remove the buds from the stems before drying on flat screens. With the other method, farmers hang stems on trellises and then remove buds after they’ve dried.
“Most growers in Pennsylvania are planning on air drying,” she said.
Snyder advised air drying under a roof and out of direct sunlight, “like in a pole barn or hoop house, shipping or storage container, or a regular barn.”
Whatever the structure, it should be well-ventilated.
The ideal conditions should be 60 to 70 degrees Fahrenheit at 60% humidity.
“Slow air drying does produce a higher quality CBD and terpenes,” Snyder said.
Removing branches from the plant and hanging can prevent mildew and mold, unlike hanging the entire plant. Or, the plants could be placed on screened trays with good airflow. Farmers also need to turn the buds so they dry evenly.
“How long drying takes is dependent on conditions, ideally five to seven days for air drying,” Snyder said. “You can over-dry your harvest. Most are shooting for 10% moisture, but I’ve (seen) 4%.”
Maximizing CBD content and minimizing THC relies largely upon plant genetics.
“It depends upon what strain you’re choosing to grow,” Snyder said.
She also added that overly dry or overly irrigated plants cause THC spikes, as does anything else that stresses the plants.
“Get the plant a good start with proper irrigation and no stress,” she said.
Some farmers choose kiln drying, which uses large boxes with heat and fans. They can dry 300 to 500 pounds in 24 hours; however, air drying is said to maintain better quality.
“If you have dust left over from drying, keep it as it may be extracted,” Snyder said.