The hemp plant is harvested for its fibers, seed, seed meal and seed oil.
Hemp is a distinct variety of the plant species cannabis sativa L. Due to the similar leaf shape, hemp is frequently confused with marijuana. Although both plants are from the species cannabis, hemp contains virtually no THC (delta-9-tetrahydrocannabinol), the active ingredient in marijuana.
Hemp cannot be used as a drug because it produces virtually no THC (less than 1%), where marijuana produces between 5 – 20 % THC.
Hemp Agronomic Characteristics
Hemp is a bast fiber plant similar to flax, kenaf, jute and ramie. Long slender primary fibers on the outer portion of the stalk characterize bast fiber plants. An annual plant that grows from seed, hemp can be grown on a range of soils, but tends to grow best on land that produces high yields of corn. The soil must be well drained, rich in nitrogen, and non-acidic. Hemp requires limited pesticides because is grows so quickly and attracts few pests. In northern latitudes, hemp is usually planted between early March and late May. Hemp averages between 2 – 4 meters in height in about four months of growth.
Hemp crops are harvested at different times for different hemp products.
Harvesting stalks for high quality primary fiber occurs as soon as the crop is in flower.
Harvesting for seed production and stalks occurs 4 – 6 weeks after flowering, when male plants begin to shed pollen.
Primary Hemp Fiber
The valued primary fibers are contained around the hollow, woody core of the hemp stalk. These long, strong fibers that grow the length of the hemp stalk are considered bast fibers Hemp fiber possesses properties similar to other bast fibers (flax, kenaf, jute and ramie) and excels in fiber length, strength, durability, absorbency, antimildew and antimicrobial properties.
Once a hemp crop has matured and been harvested, hemp primary fibers are separated from the hemp stalk through the “retting” process. For “dew retting”, the cut stalks are left in the field for several weeks to allow natural humidity and bacteria to decompose the fiber-binding pectins. Other ways to separate the fiber from the core are: water retting, warm water retting and chemical retting. When the retting process is complete, the fibers are readily separated from the core, and processed for specific products.
Primary fibers are long-staple length fibers, averaging 8 ” (20 cm) in length. These hemp fibers can be spun and woven to a fine, crisp, linen-like fabric and used for apparel textiles, home furnishing textiles and carpeting. Antimildew and antimicrobial properties make them very suitable for sails, tarps, awnings, and floor coverings.
Primary fibers can be cut to shorter staple lengths to accommodate a variety of spinning systems. Hemp fiber blended with wool, cotton, linen or other fibers, adds strength, durability, absorbency and breathability, making hemp-blended fabrics cool and comfortable to wear and touch.
Core fiber is derived from the sturdy, wood-like hollow stalk of the hemp plant. Sometimes referred to as “hurds”, it is up to twice as absorbent as wood shavings, making it an excellent animal bedding and garden mulch. It can be easily blended with lime to create a strong yet lightweight concrete or plaster. Its high cellulose content means it can be applied to the manufacturing of plastics. Like primary fiber, it is biodegradable and possesses antimildew and antimicrobial properties.
The Qualities of Primary Hemp Fiber
hemp under microscope 125 x magnification
|length||average 8 ” (20 cm) in length,|
4 – 6 ”, 1 – 2 ” and special lengths available upon request
|elasticity||low, can be treated to improve|
|heat conductivity||high, very cool fabric to wear|
|cleanliness and washability||high|
|reaction to bleaches||will weaken, use with care|
|reaction to heat||will scorch and burn|
|effect of mildew||highly resistant|
|effect of light & outdoor exposure||very resistant|
|reaction to alkalies||not affected|
|reaction to acids||easily affected|
|affinity for dyes||very good|