Planting

Grain production may be optimized with no more than 150,000 plants per acre and sowing 20 to 30 lb/ac of seed. Fiber production may be best when planting in row spacings of less than 12 inches, however, some do plant in 30’ rows. The seed rate maybe 25 to 30 lb /ac. High plant density results in tall plants capable of producing longer fibers. Hemp can be sown with a grain drill such as used for wheat. The seed weight has been estimated at 15,000 to 27,000 seed per pound (1000 kernel weight of 18-22 grams; the seed will be smaller for monoecious varieties). The seed is fragile and can be damaged during planting. With air planters, the fan speed should be set at low.

In Europe, fiber yields were not increased by having more than 182,000 plants per acre and this plant density resulted in better quality fiber than with higher plant densities. Hemp plant stands are likely to self-thin as more vigorous plants suppress the less vigorous, such as the male plants. Seed placement should be ½ to ¾ inch deep; some recommend seeding at more than a 1-inch depth in dry soil.

Soil temperature should be about 55 ^oF. Emergence is likely three to five days after spring planting. Hemp is more tolerant of low soil temperature at planting than corn and while seedlings can be killed by an early frost, hemp survived a 24^oF temperature in May in Canada.

Fertilizer

Fertilizer recommendations have not been determined for Nebraska. Penn State University has recommended 150 lb/ac N, 30 lb/ac P₂O₅ and 20 lb/ac K₂O. In a series of trials in Europe, mean fiber yield did not increase with when nitrogen was increased from 90 lb/ac to 140 lb/ac; however, in another set of trials conducted in the Netherlands, fiber yield increase as the N rate was increased to 180 lb/ac. In Alberta Canada, grain yield peaked with 110 lb/ac N and fiber yield peaked with 80 lb/ac N. The optimal P and K rates will depend on soil test values.

Weed, Disease, and Insect Management

A list of products allowed for pest control is provided by the Nebraska Department of Agriculture. Weed suppression with narrow rows, high plant density, and tall plants is important for fiber production. If planted in 30” rows, inter-row cultivation may be needed for early weed control. Hemp can be planted no-till following a burn-down application of herbicide.

There is potential for disease and insect pest problems but information and recommendations are lacking for Nebraska and other states. No pesticides are labeled for hemp in the US. Therefore, rotation of hemp with other crops may an important component of integrated insect and disease management for hemp production. Hemp may benefit other crops in rotation such as through suppression of weeds and some nematode species by hemp. In Alberta, gray mold has been a problem and rotation with canola was found to increase sclerotinia.

Harvest

Grain should be harvested when shattering begins. The rest of the plant will still be green and about 70% of the seed will be mature. The grain water content may be >20% but <20% is desired. Grain combines can be used for grain harvest and some have suggested settings similar to those used for grain sorghum. The long stems can challenge combine harvest so some have placed PVC pipe around moving parts to reduce wrapping. The header should be kept high enough to get the grain while minimizing stem that needs to pass through the combine. The cylinder speed should be 4500-6000 rpm. Much dust can be generated when the plants are dry creating a fire hazard. Move grain at low auger speeds or with conveyor belts to reduce damage.

As with any grain crop, the proper harvesting, processing, transportation, and storage are critical to prevent spoilage and ensure the highest value for the harvested grain. Hemp grain is thin-walled and fragile, requiring care in harvest, storage, and transport. A grain drying facility is needed and grain drying should begin within 1.5 hour of harvest. Drying can be at 140^oF with a continuous flow drier but grain temperature should not exceed 100^oF to avoid ‘toasting’. Hemp grain, about the size of sorghum grain, contains 29-34% oil of which 15-25% is alpha-linolenic acid (an omega 3 fatty acid) compared with 35-45% oil content for flax of which 70% may be alpha-linolenic acid.

Hemp is swath or windrow cut for fiber production at about 8” between early bloom and seed set when the lower leaves of female plants begin to yellow. The windrows are baled at 12% moisture content and the bales are transported for processing to remove and separate the bast and hurd fibers. Bast fiber concentration is highest in the "bark" of the stem while high lignin but shorter hurd fibers dominate in the rest of the stem. Therefore, wider diameter stems are preferred. Common fiber yields are 15-22% of stem dry weight. A multi-cut combine is available that harvests the upper plant for grain while windrowing the stems; it seems it works well for some varieties but not all. An alternative for harvesting both grain and fiber is to harvest these in separate passes, maybe giving the stems more time to dry before cutting for the fiber harvest.

Processing

Information is scarce. We have not learned of any large-scale commercial heap decortication facility operational in US. Small-scale hand-fed equipment is marketed on-line. Canadian Greenfield Technologies has their patient pending HempTrain™ which is described as capable of handling baled hemp feedstock and separation of the high-CBD fraction, green microfiber, bast fiber, hurd, and grain fractions. It is reported to be capable of processing feedstock at 1 t/hr.

Traditionally, hemp was left in the field for up to five weeks after cutting for retting (dew retting), a decomposition process that breaks the bonds between the outer long bast fibers and the inner shorter hurd fibers. However, dew retting is subject to weather conditions and uncontrolled with inconsistent and often negative effects on fiber quality. An alternative to dew retting is water retting which requires much clean water which should be treated before discharge. More common may be mechanical fiber separation without any retting or maybe with an enzymatic treatment.

Marketing

It appears the 2019 supply greatly exceeded demand and hemp fiber and grain feedstock prices plunged during 2019. The supply/demand discrepancy was greater for the Great Plains compared with some other areas. Rather than outright purchase of feedstock at an agreed price, processors offered growers a profit share arrangement on the product once sold. Available market information is too weak for prediction but indicates a need for caution. Some brokers and processors may be new with little capacity to fulfill obligations under adverse conditions with risks of failed contracts or delayed acceptance of feedstock. See a USDA ERS Feb 2020 report.

Hemp Production Budgets

For information on budgeting for hemp grain, fiber and CBD production, see worksheets from Pennsylvania State University and from the University of Kentucky.