Hemp has been an important fiber crop in the New England colonies since the mid-17th century. In the mid-19th century, the United States (USA) saw its peak production of industrial hemp. The states of Illinois, Indiana, Iowa, Kentucky, Minnesota and Wisconsin were the main producers of this crop. Industrial hemp (Cannabis sativa L.) is defined by law as having less than 0.3% of THC (tetrahydrocannabinol), the psychoactive component of marijuana.
It is believed that Spanish settlers brought hemp to the Americas in the mid-16th century and by 1619, Native Americans and British colonists were already growing it for fiber in New England. Hemp was used to make canvas sails for ships, and it is said to have more than 25,000 uses. Products derived from industrial hemp include fiber, grains, seeds, oil and straw and oil extracts from plant tissue (seedless) (cannabinoids). In order to ensure a successful hemp production in the USA, it is essential for producers to sign contracts with accredited buyers of industrial hemp products before planting a crop.
Research is needed to provide data on planting, management, fertility, harvesting and processing specific to production in Michigan. Meanwhile, producers in Michigan will have to rely on a variety of hemp production resources published by states such as Kentucky and Canadian provinces such as Ontario that have industrial research programs on hemp. Industrial hemp is an annual, wind-pollinated, broadleaf plant with taproots that can grow rapidly under ideal conditions. When grown for grain production, plants reach heights of 6 to 10 feet while for fiber production they can grow unbranched up to 13 feet.
For cannabinoid production only female plants are cultivated and ample space is used to encourage branching and maximize flower production. Young plants are sensitive to wet or flooded soils for the first three weeks or until growth reaches the fourth internode (approximately 1 foot tall). The soil pH should be between 6.0 and 7.5 with neutral or slightly higher than neutral being preferred. Hemp prefers a significant amount of moisture and research conducted at Ridgetown College in Ontario indicates that it needs 10 to 13 inches of rain during the season.
Hemp also responds positively to high daytime temperatures of 25°C to 28°C (77°F to 83°F). Once the third pair of leaves has developed, hemp can survive low daily temperatures of up to -0.5°C (31°F) for 4 to 5 days. Good contact between seed and soil is required to achieve the best germination rate of industrial hemp seed and a firm, level and relatively fine seedbed must be prepared. Hemp can be grown with direct tillage or with conventional tillage and planted with a standard drill bit or retransmission sowing followed by sowing in crops.
Planting should occur when soil temperatures reach 40°F or higher with 46°F being ideal for rapid germination. The best planting date is determined by soil temperature and runs from late April to late May in northern Ontario and may be similar in Michigan; however it should not be planted after the first week of June. Farmers of coarser textured Michigan soil may benefit from adding 20 to 30 pound sulfur but should avoid overfertilizing which can compromise the quality of the crop due to stem breakage and lodging. Plant population is another factor in weed control as research conducted in Canada has found that fields with a high population of plants close their canopy earlier in the season which shades weeds and reduces their growth.
Knowing which herbicides have been applied to a field in previous growing seasons is essential to avoid cumulative damage.