Production Requirements
Soil Types: Prefers well drained soils. Reduced yields on extremely heavy or light textured soil types
Soil pH: 6.0–7.5
Recommended Rotational Crops: 4-year rotation with cereals or corn
Should not plant after: canola, edible beans, soybeans, buckwheat or sunflowers
Minimum Soil Temperature: 4°C–6°C (seedlings are sensitive to frost)
Optimum Air Temperature: 25°C–28°C
Earliest Planting Date: Early to late May
Required Growing Season: 70–90 days for fibre crops and 100–200 days for grain crops
Hemp (Cannabis sativa) is an annual crop grown for specialty grains, oils and personal care products. It can also be grown as industrial fire for textiles, paper and biofuels markets. Currently grain is the main market for hemp in Ontario.
Industrial hemp is a controlled substance and may only be grown under license from Health Canada. Health Canada controls the importation, production, processing, possession, sale, transportation, delivery and offering for sale of industrial hemp. Only varieties named in the “List of Approved Cultivars” published by Health Canada are approved for planting. All industrial hemp grown, processed, and sold in Canada must contain 0.3% tetrahydrocannabinol (THC) or less in the leaves and flowering parts. In addition, a maximum level of 10 parts per million (ppm) for THC residues in products derived from hemp grain, such as four and oil has been set under the regulation. Information about varieties, licenses and regulations may be obtained by contacting Health Canada’s Office of Controlled Substances or hemp@hc-sc.gc.ca.
Description
Different cultivars are grown for fibre and seed. When grown as a fibre crop, hemp grows to a height of 1.5–3 m (5–10 ft) without branching. In dense plantings, the bottom leaves atrophy due to the exclusion of sunlight. The stem has an outer bark which contains the long, tough bast fibres for which hemp is renowned. The centre core contains the hurds, or short fibres, that are useful in many other applications such as animal bedding.
Soil Conditions
Hemp responds to a well-drained, sandy loam soil with a pH range of 6.0–7.5.
The higher the clay content of the soil, the lower the tonnage of fibre that will be produced. Clay soils are easily compacted, and hemp is very sensitive to soil compaction. In well-structured and well-drained soils, the tap root may penetrate 15–30 cm (6–12 in.) deep. In compacted soils the tap root remains short and the plant produces more lateral fibrous roots.
Tillage and Seedbed Preparation
Hemp seed requires good seed-to-soil contact. The seedbed should be firm, level and relatively fine, similar to that prepared for direct-seeded forages. The soil can be worked and planted as soon as the ground is dry enough to avoid compaction.
Planting
Plant seed in 15–18 cm (6–7 in.) row spacing at a depth of 3 cm (1.25 in.). The optimum soil temperature for rapid germination is 8°C–10°C, although hemp seed will germinate at 4°C–6°C. Early planting produces taller plants with higher fibre yields. The optimum final population for fibre production is about 200–250 plants/m2 (19–23 plants/ft² or 810,000–1,000,000 plants/acre). For seed or grain production, the optimum final plant population is around 100–150 plants/m2 (9–14 plants/ft² or (400,000–610,000 plants/acre).
Hemp is a heavy user of moisture; therefore, it is important to make use of early soil moisture and to obtain a good ground cover early to reduce surface evaporation. For grain production, about half of this moisture is required during flowering and seed set.
Seedling plants can tolerate a light frost and will continue to grow at temperatures as low as 2°C. After the third pair of leaves has developed, hemp has been known to survive temperatures as low as -5°C for 4–5 days. During vegetative growth, hemp responds to daytime high temperatures in the range of 25°C–28°C.
Fertility Management
Limited Ontario fertility guidelines exist. Hemp requires approximately the same fertility as a high-yielding crop of wheat. Research is continuing to fine-tune exact nutrient requirements. Apply up to 110 kg/ha (98 lb/acre) of nitrogen, depending on soil fertility and past cropping history. Phosphorus and potash fertility should be at target soil test levels (12–18 ppm P and 100–130 ppm K). If soil phosphorous and potassium levels are below target ranges, incorporate these nutrients into the soil ahead of planting, at rates that meet the crop removal rate plus an amount that will build up the soil test over time.
Weed Control
If hemp is planted in well-drained, fertile soil under nearly optimum temperature and moisture conditions, it will germinate quickly and reach 30 cm (1 ft) in 28–35 days from planting. At this stage it will give 90% ground shade and weed growth suppression by the exclusion of light from the soil. Under rapid growing conditions, hemp at a final population of 200–250 plants/m2 will suppress nearly all weed growth for that season. For more information, see OMAFRA Publication 75, Guide to Weed Control.
Harvest and Storage
Harvest
Harvest depends on end use:
- Textile fibre: harvest at flowering after pollen shed but before seed set, approximately 70–90 days after seeding.
- Industrial fibre: harvest any time after flowering. Hemp fibre that is cut after seed harvest has lignified considerably and is only usable in coarse industrial fibre applications.
- For fibre: when harvested using standard field-crop equipment including sickle mowers, haybines and balers, expect problems with frequent plugging.
- For grain: harvest should occur when approximately 70% of the seed is ripe and when seed begins to shatter (22%–30% moisture content), which is approximately 100–120 days after seeding. Most older model combines will require some modification to prevent plant fibre from wrapping around shafts, chains, etc. This includes use of rubber belts to cover the chains in the feeder-house and covers over any shafts (Photo 7–1).
Dry stem stalk yields in Ontario have ranged from 6.4–19.8 t/ha (2.9–8.8 ton/acre) of dry, retted stalks per acre averaging 7.4 t/ha (3.3 ton/acre).
Retting and Turning
Retting is the process of beginning to separate the bast fibres from the hurds or other plant tissues. It is done in the field, taking advantage of the natural elements of dew, rain and sun, or under controlled conditions using water and/or chemicals. The method chosen depends on the end use of the fibre.
Successful field retting requires a delicate balance of nightly dews and good daytime drying conditions. Southern Ontario climate may dictate that field retting should be done no earlier than the end of July in order to ensure adequate dew conditions. The length of the retting process is critical for optimum fibre yield and quality. It typically takes 12–18 days to complete. The windrows are turned vigorously, once or twice, with a tedder or windrow inverter to facilitate uniform retting of the windrow and to knock the leaves of the stems. Excessive leaves will hinder drying and may cause the straw to contravene the Controlled Drugs and Substances Act, 1996.
Baling and Storing
For fibre-hemp, stalk moisture should be less than 15% at time of baling and should continue to dry to about 10%. Baling can be done with any kind of baler. Large round, soft-core balers may be most satisfactory to allow bales to dry more quickly in storage. Bales must be stored indoors under dry conditions to stop the retting process before the fibres become rotted. Bales stored under plastic, based on experiments with hay storage, would indicate that moisture would be wicked up from the ground and some spoilage would take place. Bales placed on pallets will have less spoilage.
Dry grain hemp to 12% moisture for storage. Store in a cool, dry environment.
Insects and Diseases
More than 50 different viruses, bacteria, fungi and insect pests are known to affect hemp. However, hemp’s rapid growth rate and vigorous nature allow it to overcome the attack of most diseases and pests.
As the concentration of the hemp crop and alternative disease hosts increase in a given area the number of, and population of organisms will tend to increase. A number of pests have been noted in hemp fields in Ontario including common moulds of hemp, Botrytis cinerea (gray mold) and Sclerotinia sclerotiorum (white mould). Sclerotinia also affects soybeans, edible beans, canola, buckwheat and sunflowers. The effect of these diseases on hemp (and hemp as an alternate host) may not be known until hemp is grown more intensively in bean and canola growing areas. Fusarium lesions have been noted on the roots of hemp plants. European corn borer has affected some stands in southern Ontario.
A limited number of pesticides are registered for hemp in Ontario. Crop rotation would appear to be the best cultural practice to avoid disease build-up until more is known about hemp’s susceptibility to disease organisms. A 4-year rotation is recommended. Hemp should not follow soybeans, dry edible beans, canola or sunflowers.
Wind and hail damage can be significant in the hemp crop. Tall plants with lots of high leaves can be bent over quite easily by mid-to late-summer storms. Broken plants will partially recover if not broken too low on the stalk.