In Colorado, hemp grown for fiber will more closely match existing cropping systems than hemp grown for CBD oil. Fiber hemp hurd for hempcrete, hemp hurd powdered (green microfiber) or hemp hurd bast fiber could increase diversity for current rotations, but will offer some challenges. Hemp production for fiber can be highly mechanized with labor demands per acre similar to that of other agronomic crops, except for weed control and harvest operations which require relatively more time for hemp.
Hemp Fiber Seed or CBD Hemp Seed Varieties
Varieties of hemp, whose stems are used for fiber grow to 6-7 feet in height, providing the desired long fibers for industrial processing. Varieties there are two types Fiber Seed or CBD Seed, the Fiber Seed is striaght fiber which will be more fragile and harder to manage, the CBD seed is a CBD plant, the stalk and the fiber (straws/sticks) are much more meater and fuller. For the Fiber Seed there are some such as ChinMa (China), Katani (Canadian), CRS-1 (US), CFX-2 (US), Futura 75 (Spain), and Futura 77 (Spain). For the CBD Seed, either Cherry Hemp Seed or Cherry Blossom Hemp Seed would suffice. Hemp varieties should be certified as having <0.3% THC.
For our organic industrial hemp farm, we like using the CBD hemp seeds, because from a CBD stalk you can get various ways of selling products from your crop (biomass, crude, distillate, isolate), not just hemp fiber (hemp hurd, hemp hurd powder, hemp bast fiber). For us we rather carry all the different products above, not just fiber.
The fiber yield is likely to be less with earlier-maturity varieties than later-maturity varieties because cellulose concentration and yield increase as the season progresses. Normally, male plants die off during the season and monoecious female varieties are generally preferred for industrial hemp production.
Planting For Hemp Fiber
For Hemp Fiber production is best when planting in row spacings of less than 12 inches, however, some do plant in 30 foot rows. Your planting season should be in mid to late-May. The seed rate maybe 25-30 lbs/per acre. Seed placement should be ½ to ¾ inch deep; some recommend seeding at more than a 1-inch depth in dry soil. We recommend using 7-8” between rows for quick canopy closure and weed suppression. Soil temperature should be about 55 – 75 °F. Emergence or sprouting is likely 3 to 5 days after spring planting. Hemp is more tolerant of low soil temperature at planting than corn and while seedlings can be killed by an early frost, hemp can survived a 24°F temperature, but not for a sustain period of time. The hemp plant should reach 10 – 15+ feet, the taller the better – long slender stems.
Harvest for Hemp Fiber
When male plants are at starting to flower – this will be mid-August. You can cut with a sickle-bar or disc mower. Hemp fiber should be harvested when shattering begins. The long stems can challenge combine harvest so some have placed PVC pipe around moving parts to reduce wrapping. The header should be kept high enough to get the grain while minimizing stem that needs to pass through the combine. The cylinder speed of the combine should be 4,500-6,000 rpm (roughly). Hemp is swath for fiber production at about 8” between early bloom and seed set when the lower leaves of female plants begin to yellow.
The windrows are baled at 12% moisture content and the bales are transported for processing to remove and separate the hemp bast fiber and hemp hurd fibers. Bast fiber concentration is highest in the “bark” of the stem while high lignin but shorter hurd fibers dominate in the rest of the stem. Therefore, wider diameter stems are preferred. Common fiber yields are 15-22% of stem dry weight.
Retting For Hemp Fiber
Retting is a controlled rotting process that loosens the fibers from the hurd. Cut green stalks are left in the field 2-6 weeks to “ret”. This relies on fungi and bacteria to degrade pectin binding fibers to the hemp hurd. Then it turns brown to gray color, some charcoal covered spots. Natural separation of the fiber from the hemp hurd during the retting process. Indication the stalks are properly retted. Further retting leads to decline in fiber.
Traditionally, hemp was left in the field for 2-6 weeks after cutting for retting (dew retting), a decomposition process that breaks the bonds between the outer long bast fibers and the inner shorter hemp hurd fibers. However, dew retting is subject to weather conditions and uncontrolled with inconsistent and often negative effects on fiber quality. The recommended approach is the mechanical fiber separation without any retting or an enzymatic treatment.
Baling For Hemp Fiber
We recommend you getting 1-ton round or square bales. The moisture content – 16% or below to avoid molding (this very important), <10% may result in brittleness and impact fiber quality. Somethings to avoid contaminating weeds in bales and getting any plastic or debris in bales. Do not bale up stones as they will cause damage to farm and factory equipment as it may become lodge in bottom of bales sitting on gravel. Make sure you store bales in dry conditions. Rewetting of the bale leads to rotting of stalks and the bale falling apart. For the round bales resist water damage and rotting better. For the square bales are easier to stack but need to be covered. Higher value stalk material for textiles should be stored in a protected environment (i.e., barn or warehouse).