CANNABINOIDS (FLOWER) PRODUCTION
This area of hemp production agronomy has the lowest level of optimization – many different approaches are being explored at this point. This is not surprising since the CBD market has only become mainstream in the last 5 years, following legalization of hemp production. Many of the agronomic practices for flower production are similar to grain production so we refer you back to the GRAIN section for topics such as planting date, fertility and weed management. The two issues of debate today are: 1) planting method which will depend on the planting stock chosen (feminized seed, dioecious seed, clones, etc.); and 2) harvest method which is also impacted by the planting stock. We address each below.
Much of the production today is done using clones or feminized seed with the end goal of fields containing only female plants. This is an intuitive approach since the female reproductive tissue (e.g. the buds) produces the valuable cannabinoids, and both approaches can control gender if they are done correctly. It also serves the purpose of eliminating, or at least minimizing, seed production, which is perceived as important by many flower producers. The all-female production method comes with some notable tradeoffs:
- High cost: clones and feminized seed are expensive to produce since this work in its entirety or partially conducted in greenhouses and requires intensive management practices (See FAQs: What is Feminized Seed?). This creates high economic risk for crop failure due to uncontrollable environmental factors such as hail or disease. It has also has led producers to plant at lower densities, ranging from 2,000 to 5,000 plants/acre in order to maximize the total yield per plant. These lower planting densities create the next tradeoff, weed control.
- Poor weed control: as mentioned above, commercial grain production is typically planted at a density of 500,000 plants per acres so that each acre of a dioecious cultivar contains around 250,000 female plants. In other words, about 100 times more than an all-female field! This density follows traditional agronomy theory which seeks to minimize bare ground in order to control weeds more effectively. The low density of all-female production necessitates high weed control costs or a tolerance of a high weed seed bank in the following years.
- Male pollen is difficult to control: hemp pollen is small and can be carried by wind for many miles (Small and Antle, 2003). This puts all-female hemp crops at risk of being pollinated by unknown fields with males, thus making the high input costs dubious. Further, most feminized seed providers do not guarantee 100% female seeds in their seed lots so walking fields to remove the rogue male is common practice and adds another production cost. It also presents a risk because even a single male plant can create tens of millions of pollen grains (Small and Antle, 2003). This means a single male plant can produce a significant amount of seed.
How do I harvest flower most efficiently?
The answer to this question must be made with several considerations in mind. First, as with harvesting any product, the method must maximize harvest of the mass per unit area harvested. Second, it must minimize loss of the glandular trichomes which contain the highest cannabinoid concentrations (See FAQs: What do we know about cannabinoids?). Trichomes are small and fragile so their loss during harvest is a legitimate concern. Finally, the method must incorporate a step for effectively sorting seed from flower. Hemp seeds have no cannabinoids so if they are present in the flower, the cannabinoid content of the seed/flower mixture will decrease. The following are brief descriptions of the methods we have reviewed. NWG does not endorse any of these methods (yet!) We will continue to update this page with our own data as we complete our experiments.
- Head or whole plant harvest: the principle here is similar to straight cutting grain except that rather than threshing the head, it is harvested into a truck for indoor drying and threshing. By threshing indoors, more control can be applied to trichome loss by collection with vacuum system.
a. A video of a head harvesting system: Watch Video
b. A video of a whole-plant harvesting system: Watch Video
- Harvest with a combine: this will be similar to grain harvest except that the combine settings are modified. The specific settings are not well-established but the main changes include lowering fan speeds and removing sieves with the intent to minimize loss of product other than the stalk. In this case the flower or flower/seed bulk is augered into the grain bin and then moved indoors for drying and processing. The crop can be windrowed in dry climates to expedite drying but care must be taken to harvest the crop before it becomes too dry in order to minimize trichome loss.
a. A video of flower harvest with a combine: Watch Video
- Stripper header: a stripper header is not a common implement on US farms but it has some practical benefits for harvesting a hemp field. It operates just as the name would imply, the header strips the flower (and grain if present) leaving the stalk remaining in the field.
a. A video showing a stripper header harvesting wheat: Watch Video
b. A brief video showing what a field might look like after harvest with a stripper header: Watch Video
- Silage bags: This approach is built upon the practice of wet preservation commonly used in fodder production. In short, a forage harvester is used to chop and collect the entirety of the hemp crop. This means that the stalk, stems, the leaves, the flower and any seed that may be present are all harvested. This is expected to lower the cannabinoid percentage considerably since stalks, stems, leaves and seeds are considerably lower in cannabinoid content than the flower. The chopped, wet biomass is then placed into silage bags and the air is removed. What is unclear is the quality of the final product. Watch Video
Our position is that dioecious cultivars optimized for cannabinoid production is the only economically feasible approach to scaling production of these valuable compounds. It is based on the power of seed multiplication that all large-acreage commodity crops have utilized to create planting seed cost effectively. We expect the harvest methods will continue to innovate and adjust to continually improve yield. Regardless of method, NWG will continue to create planting seed that provides the farmer with a true dual-purpose, de-risked, profitable crop.