We had some chilly nights last weekend and the beginning of the week, which caused concern for some hemp growers. But, we made it through and the hemp seems to be doing alright. There are some noticeable changes in color, which could cause alarm, other than that, the hemp is unscathed. One cultivar at Meigs went from a bright green to a deep purple. The same thing happens to the forsythia in my front yard and to many other plants this time of year.
Most of the data on frost tolerance and hemp is out of Canada and focuses on grain and fiber specific cultivars. Growers have harvested all the fiber hemp and most of the grain hemp. However, there is not much data on frost tolerance in cannabinoid rich hemp. The University of Vermont does have some useful information on their experiences with frost and hemp. They find that mature plants can handle frost temperatures of 29-32°F, but a moderate freeze of 25-28° can damage some vegetation, and temperatures of 24°F or colder can cause heavy damage to plants (UVM Hemp and Cold Temperatures). They do not discuss duration of cold temperatures or cultivar differences, but it gives us a helpful starting point to better understand frost tolerance. They also believe that frost and the change in color does not necessarily mean a change in cannabinoid content. One Indiana grower has noticed that purple hemp plants are more likely to fade to a brown color once harvested and stored compared with hemp that was harvested green. There is not a degradation in quality, but the color could worry some growers.
What is interesting about the hemp at Meigs, are the two cannabinoid hemp cultivars reacted differently to the frost. The cultivar Eclipse turned a deep purple color and appears to be unharmed by the frost. The other cultivar, Cherry Wine, did not turn purple or red and also appears to be unharmed. It is possible that Cherry Wine will not change color during a frost, or that it will take much colder temperatures to change it. According to the weather data from TPAC, the coldest it got was 32°F and it was not cold for long. The two week forecast does not show temperatures dipping below freezing, so for growers who are still waiting to harvest, it does not look like you have to worry about frost damage.
Hemp at Meigs on Oct. 1 (C. sativa ‘Eclipse’).
Hemp at Meigs on Oct. 8 (C. sativa ‘Eclipse’).
Hemp at Meigs on Oct. 8 (C. sativa ‘Cherry Wine’).
