Hemp Harvest Timing and Drying
We are just now starting to research harvest timing with hemp grown for CBD and don’t have much information on which to base recommendations. Probably the best way to time harvest is to monitor trichome color in combination with at least weekly testing for CBD and THC levels. Trichomes start off clear and turn an opaque white when maturing. After that the trichomes start to turn amber. If all the trichomes on a plant matured at the same time, harvesting when they turn opaque white would probably work. Unfortunately, they do not mature at the same time. Our best guess from observations last year is to harvest when 20-30 % of the trichomes have turned amber. Many growers are supplementing this technique with weekly or biweekly samples to indicate where they are in terms of CBD and THC levels. The level of THC your processor may accept could have an impact on when you harvest.
In the picture above you see how the trichomes progress from clear to milky white to amber. You will need some magnification to see this clearly.
We have seen several methods for drying hemp. Using tobacco barns is probably the Cadillac system, but people have been successful with drying in buildings or barns if they could maintain good airflow and keep humidity at 60% or less. Remember that after you dry the hemp you have to keep it dry or it will absorb moisture and may mold. I have seen some growers add heat and be successful, and some be successful without adding heat. One of the common recommendations going around is to add heat to get 20 degrees above ambient temperature. Until we have more research I would not go above 100 degrees.
George Place, the county Extension Director in Catawba County wrote a good article on How to Harvest and Dry Hemp for CBD.