Hemp Grain Production
Hemp grain production is more similar to other grain crops than to hemp fibre as the crop grows for a longer time, pest monitoring and control is important, time of maturity is critical to harvest and the key yield is in clean graded grain/seed.
Hemp Seed/ Hemp Grain Production
Hemp for seed/ hemp grain is planted in late Summer or early Autumn depending on variety, grown through Autumn, usually with irrigation. It is sown at lower densities than for fibre, usually aiming for about half the number of plants/m², sowing at 25-40 kg/ha depending on variety and conditions.
Early husbandry is similar for hemp fibre, ensuring adequate moisture but not overwatering if an irrigated crop. Fertiliser regimes are as for fibre hemp with adjusted lower N and higher P than for fibre crops.
At the onset of flowering the crop will differentiate into male and female flowers (about 50% each). The males flower first, having a “flower spike” that stands out above the crop, releasing pollen from many small flowers. The female flowers are less visible and appear as tightly bunchy heads, surrounded by small leaflets and bracts, with “hairs” that are actually the pistillate component of the female flower. The seed is wind pollinated and is susceptible to front and rain damage at this time.
Flowering and seeding hemp should be monitored for insect attack by sucking and chewing insects such as Green veggie bug (Nezaria viridula) and Heliothis grubs (Helicoverpa spp.). These should be controlled if populations reach levels of economic damage.
Harvesting Hemp Seed/ Hemp Grain
Seed or hemp grain matures usually four to six weeks after peak flowering as nitrogen and moisture reserves are depleting. Seed heads mature from the bottom up and the seed is mature once the seed coat has hardened and the surrounding bract has dried.
Harvesters used on grain crops of hemp include rotary headers or conventional headers with a Draper front conveyer system. Both ground and drum speeds should be slow relative to other grain crops. The stalk flow is extremely important in relation to the entangling of the head and stalk material through the machine. The use of straw choppers should be avoided as additional moving parts only allows fibre to wrap around this mechanism.
Seed and hemp grain should be dried to less than 8% moisture before storing. Cold storage prolongs the viability of the seed as oils in the seed degrade rapidly at daytime or higher temperatures.