Industrial hemp grows best in well drained, loam soil. The optimum soil pH (acidity) for hemp cultivation is above 6.0pH. Neutral to slightly alkaline (pH7.0 – 7.5) is preferred. Higher clay content soils can lower the yield of grain or fiber. Clay soils are easily compacted and hemp is very sensitive to soil compaction. Young plants are very sensitive to wet soils or flooding during the first 3 weeks or until growth reaches the fourth internode (approx. 30 cm or 12” tall). Water damaged plants will remain stunted, resulting in an uneven and poor crop.
Hemp can be planted earlier than corn in most areas because hemp grows well at low temperatures and can tolerate some frost exposure. Hemp grows best when mean daily temperatures are between 60º-80º F. However, hemp can handle both colder and warmer conditions. During the vegetative growth period hemp responds to daytime high temperatures with increased growth and water needs. After the 3rd pair of leaves develop it can survive daily low temperatures as low as 31.1ºF for 4-5 days.
Hemp plants require abundant moisture during the first six weeks of growth. Soil requires approx. 3-400mm (10-13”) of rainfall equivalent. It is important to make use of early soil moisture and to get early ground cover to reduce surface evaporation, as well as maintain good weed control. Once well rooted, hemp can endure drier conditions. Crop water usage varies depending on local soil and climatic conditions. Good soil drainage is important to maximize hemp production.
About half of the moisture is required during flowering and seed set to produce maximum grain yields. Drought during the flowering and seed set stage can produce poorly developed grain heads and results in low yields of light grain.
Research is needed to determine the amount of water needed and whether irrigation is required for the cultivation of hemp in the Pacific Northwest.
Hemp requires approximately the same fertility as a high-yielding crop of wheat. The recommended fertilization rates for hemp are N ‐ 70 – 100 lbs/acre; P ‐ 0 – 45 lbs/acre; K ‐ 45 – 178 lbs/acre
Approximately 42% of the plant’s biomass returns to the soil in the form of leaves, roots and tops. These contain over half of the nutrients applied to the crop and many of these nutrients will be available to help feed the following crop.
Hemp grows well as a rotational crop with a variety of other plants, including: potatoes, perennial grasses, legumes, and barley. A 4-year crop rotation is recommended as a good practice to avoid disease build-up. Do not grow on the same fields following canola, edible beans, or sunflowers.
Industry representatives have reported that a winter wheat crop that is planted following a hemp crop can increase the yield of the wheat crop by 10-15% and will require less fertilizer.
Hemp is very competitive with weeds. When grown under favorable conditions no herbicides are generally used. Hemp’s weed suppression is one of the greatest environmental and agronomic benefits of growing hemp in rotation with other crops.
Two primary diseases that can affect hemp are Sclerotinia sclerotiorum (Hemp Canker) and Botytis cinerea (grey mold).
On small acreages, good quality sickle-bar mowers and hay swathers have been used to cut. Frequent plugging has been a constant problem with this equipment. It is important to keep knives sharp and in good repair at all times.
When hemp is grown for both grain and fiber it is necessary to re-cut the tall stalks after combining. A combine can be modified to perform both functions at the same time by mounting a sickle-bar mower under the header to operate close to the ground.
Retting, or rotting, is the process of beginning to separate the bast fibers from the inner hurds. Two common methods of retting are field or dew retting and water retting. The length of the retting process is critical for optimum fiber yield and quality. Retting can take between 14 days to 28 days to complete. Dry weather and low dew conditions may require longer retting periods.
Baling can be done with any kind of baler. Large round, soft-core balers allow bales to dry more quickly in storage.
Modifications can be made to conventional combines to harvest hemp grain. Recommended combine settings are cylinder speed at 250 rpm, fan speed at 1070 rpm, 1/8-inch sieve and 3/8-inch chaffer, concave set tight. Straight/direct harvesting is preferred over swathing. Grain should be combined at 18-25 % moisture. Grain should be dried to 8% moisture.
Research is required to determine actual production costs for Pacific Northwest farmers.
Yields and Price Per Acre Revenue:
Air-dry stem yields range from 2.5-14.0 metric tons of dry, retted stalks per hectare (1 to 5 tons/acre) at 12% moisture. Approximately one ton of bast fibre and 2-3 tons of core material can be decorticated from 3-4 tons of dry-retted straw.
In Canada, an estimated yield of 1,100 pounds of hemp seed per acre translates into a gross revenue of between $990 to $1,100 per acre. Farmers report $200-$300 per acre profit. Industry representatives from Canada have presented that organic hemp seed sells for almost double the price of non-organic seed.
U.S. States Cultivating Industrial Hemp:
A few farmers cultivated hemp in Colorado in 2013. The harvests in 2013 were the first hemp harvests in the U.S. in 56 years. During 2014, the Colorado Department of Agriculture issued licenses for both research and commercial cultivation. Over 197 fields were registered. The Colorado Department of Agriculture has not faced interference by the DEA.
The Kentucky Department of Agriculture licensed seven agricultural pilot programs for industrial hemp research with Kentucky institutions of higher education during the 2014 production season. At least five private farmers were also granted research licenses. Although the Kentucky Department of Agriculture faced some interference by the DEA with the initial importation of hemp seed, a formal process for the importation of hemp seed by the Kentucky Department of Agriculture has been approved by the DEA.
The Vermont Agency of Agriculture registered at least 15 farmers for hemp cultivation for the 2014 production season. Those farmers cultivating in Vermont are likely developing a seed stock for the 2015 production season. The Vermont Agency of Agriculture has not faced interference by the DEA.