By Charles Wortmann, Ismail Dweikat
Hemp grown for CBD is a high-value crop grown more as a horticultural than as an agronomic crop. It has a high labor demand, putting US production at a disadvantage with production in China and other countries with relatively inexpensive labor.
Research in Nevada has identified two varieties of hemp, Cherry Wine and Berry Blossom, for high pharmaceutical-grade CBD yield. The seed of high CBD varieties is scarce and very expensive. High CBD varieties are generally grown only as female plants, as the combination of male and female plants leads to seed production and decreased CBD yield. Breeders continue to improve the processes for creating stable feminized seed and plants. Farmers need to be wary of the source of their feminized seed stock and to check test results for validation of feminized seed. Hemp varieties should be certified as low THC with evidence that the plants produced will have less than 0.3% THC.
Farmers need to know state regulations for testing hemp for CBD and THC. (Nebraska regulations for hemp production are expected to be released for the 2020 crop season.) Some states require testing for THC within 30 days of harvest. If the THC level is too high, the crop may no longer meet the legal definition of hemp and need to be destroyed. Again, THC is expected to increase with stressful growing conditions.
CBD varieties have short plants with much branching, growing as squat bushes. The suggested spacing at this time is 2-4 feet x 6 feet. Planting practices may change for higher plant densities when seed supply is sufficient to greatly reduce the cost of seed. Given the high cost of seed, seedlings should be produced in a greenhouse for transplanting. If planting more than five acres, machine transplanting is recommended. Plants can also be produced from cuttings with similar vigor and productivity compared to plants from seedlings. Propagation from cuttings may improve plant uniformity and is a means to all-female plants.
The CBD levels can be much reduced by cross-pollination with industrial hemp or marijuana. It’s important that CBD plants are well-separated by distance or time of pollination from hemp weeds or another hemp crop.
The highest concentration of CBD is in the bracts of female flowers but CBD oil may be extracted from the whole plant. Otherwise, the harvest may be by topping plants for the harvest of mostly leaves and flowers or by picking the leaves and flowers from the plant. The ground-up plant material is soaked in grain alcohol or ethanol to extract the CBD oil. After soaking, the mix is pressed to extract the liquid. The alcohol is then evaporated off leaving the CBD oil.