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KANKAKEE, Ill. — The agronomics of a “new” Illinois crop were detailed in a recent SoilBiotics seminar.
About 22,000 acres of industrial hemp were issued permits in 2019, the first year the multi-use crop was available for licensing in the Prairie State after the General Assembly’s approval last spring.
Todd Zehr, SoilBiotics founder and owner, has worked both nationally and internationally with industrial hemp growers and gave insight into the crop that has been cultivated for centuries, including in the Midwest until the 1950s.
The commonly grown commercial hemp crop segments are:
• Hemp for fiber and other industrial uses such as paper, clothing, insulation and plastics.
• Hemp for seeds such as seed for production agriculture, food, nutritional and cosmetic products.
• Hemp for cannabidiol, or CBD oil.
Zehr stressed the major considerations that must be addressed before the first seed or seedling is put the ground — research your market and decide on the right hemp to grow in your region, identify and communicate with processors, identify the source and seed quality and make sure the right equipment and personnel is available to handle the crop.
“If you’re going to start growing it, just do something very small, even if it’s just one acre. Do one acre, find out how much work that is and then multiply it up if you want to expand and then you’ll know where you need to be with your labor, equipment and things like that. This is not a cheap project to get into,” Zehr said.
Before digging into the agronomics, Zehr said hemp can be grown from a clone, seed, or via auto-flower, and only female plants should be used. The male plants will fertilize the female plants resulting in only males, and the plants won’t produce buds, only a lot of seed.
“The male plants have to be taken out, no different than a seed crop. Also, both marijuana and hemp can hermaphrodite. It can go from male to female. Usually when it’s under a lot of stress is when it will hermaphrodite from say a female to a male,” Zehr said.
“We have to make sure we have a good growing environment, we’re feeding it a good nutritional diet, giving it plenty of good, clean water and just trying to keep this plant as healthy as possible because there are no herbicides, insecticide, pesticides that can be used on this crop.”
Here are the agronomic details Zehr presented.
THC Level Restrictions
The Tetrahydrocannabinol intoxicating ingredient concentration of industrial hemp should be no more than 0.3% on a dry weight basis. By comparison, the average level of THC of marijuana purchased legally in Colorado contains more than 18%, 60 times more THC than industrial hemp.
Back in the 1970s and 1980s, THC levels of some of the marijuana that was coming into the state illegally had THC levels of about 6% or 7%.
Soil Type
Hemp grows best on a loose, mellow, well-aerated loam soil. It is possible to grow on well-drained or tiled clay soils, but not poorly-drained clay or poorly structured soils.
Standing water could cause disease and insect issues. Sandy soils can grow hemp with adequate irrigation and fertilization, but the additional costs could make production uneconomical.
Tillage & Seedbed
Since there are no labeled herbicides for hemp, fall tillage and spring burndown is recommended — spring burndown not with chemicals, but more so with tillage. Some type of mechanical tillage will be needed.
A well-prepared, loose and level seedbed is best for germination and growth, no different than in corn and soybeans production. Make sure ground either has tile or good drainage.
Nutrients
Hemp needs growing environment with high fertility and good organic matter content, 3.5% or higher. It can be grown on lower organic matter, but it will require more fertility feeding.
The plant will pickup 60% of its nutrients from the root system and you have 40% you can provide through foliar spray to finish that off.
For optimum performance, hemp requires a soil with NPK levels much like corn. It prefers a pH of 6 to 7.5.
Soil testing is recommended before the hemp is put in the field. Hemp does not like salt and it does not like heavy metals. So, don’t just throw 32% or 28% on the plant because that will increase THC levels and reduce CBD levels.
Hemp for CBD plants are transplanted and a root treatment pre-plant is helpful. The root treatment helps with transplant shock.
In-season, hemp for seed and hemp for CBD can have a “veg” product foliar applied for increased plant size and vigor and a “bloom” product foliar applied later for better seed fill and, for CBD plants, larger and denser buds.
Water
Hemp needs good soil moisture at planting time and needs some rain or irrigation for approximately four to six weeks after planting. If you’re pumping water out of a creek, make sure it is tested because if the water is really high in nitrates, those nitrates are going to get loaded right up into that plant.
The plants will scavenge everything, not only nutrients, but the bad stuff. Overall, hemp is generally more drought tolerant than other plants during the growing season.
Planting Date
Hemp does not like cold weather or cold feet. Soil temperatures of 46 to 50 degrees are needed for good germination.
Hemp should be planted after there is any danger of hard freezes. Timing should be a little before corn is planted. Adequate soil moisture is necessary for germination.
Planting
The seed rate is specific to each variety, and this information should be sought from the supplier. Both grain/seed and fiber hemp can be planted using a standard grain drill in 6- to 8-inch rows.
Fiber hemp also can be broadcast directly. CBD hemp is planted using transplanter equipment or by hand for small plots. Zehr spaces the plants anywhere from 1.5 to 2 feet apart, depending on the variety.
Planting Rates
Seed hemp: Direct seeded at a rate of approximately 25 to 40 pounds per acre, approximately 27,000 seeds per pound. Competition between plants should be minimized to produce the highest quality seed and oil. For grain production, a good final plant population is around 10 to 15 plants per square foot.
Fiber hemp: Fiber hemp crops are planted at a rate of approximately 40 to 80 pounds per acre, higher if germination is low and seeds are large.
This high density is needed to produce higher quality primary bast fiber, the outside part of the plant that give it a rigid structure, as opposed to the core fibers inside the plant. The bast fiber content increases with plant density.
Large quantities of hemp seeds must be planted to establish crop density and suppress weeds. Final stand density should be approximately 30 to 35 plants per square foot of fiber hemp.
CBD hemp: Densities can range from 1,000 plants per acre up to 2,400 plants per acre. But make sure you know your variety very well and that will determine what your planting space is going to be. Most growers planting cannabinoids will transplant seedlings from feminized seeds, or clones cut from mother plants.
Diseases
The fungal pathogens gray mold (Botrytis cinerea) and white mold (Sclerotinia sclerotiorum) have been reported to infect and impact industrial hemp production.
Hemp also is prone to numerous fungal and bacterial leaf spots, viruses and Pythium root rot and blight during establishment. Pythium root rot is a big problem during establishment.
Diseases are caused by pathogens in the residue. Insects will also lay eggs in the residue. Good things come from residue management.
There’s the nutritional value that goes back into soil that’s 100% available for that plant for the next growing season, plus disease and insect issues are eliminated with residue management.
Insects
European corn borer and armyworm have been the insects most reported to have done damage to hemp crops across the central United States. Additional pests of concern include corn earworm and Eurasian hemp borer.
Pesticides
No insecticides, herbicides or fungicides are registered for use on hemp in the United States. Certain 25(b) products are registered to use on hemp in some states. Check specific state regulations.
These products have ingredients that have been deemed minimum risk by the EPA, but are not necessarily that effective. For now, crop rotation is the only management option available to avoid disease build-up until more is known about hemp’s susceptibility to disease organisms. A four-year rotation is recommended.
Growing Season, Harvest — Fiber
Hemp for fiber will take approximately 60 days to grow a crop. Hemp is cut for fiber production between early bloom and seed set when the lower leaves of female plants begin to yellow.
It is left in the field for up to five weeks for retting, a decomposition process that breaks the bonds between the outer long bast fibers and the inner shorter hurd fibers.
The hemp is then raked into windrows two or three times for drying and to remove leaves. When dry, the windrows are baled and the bales are transported for processing to remove and separate the bast and hurd fibers.
Bast fiber concentration is highest in the “bark” of the stem while the high lignin, shorter hurd fibers dominate in the rest of the stem. Therefore, wider diameter stems are preferred.
In planning their cropping programs, growers will need to account for having the proper equipment for cutting, turning and collecting retted plants from the field and then delivering the crop to fiber processing facilities.
At processing facilities, a machine called a decorticator strips the bast from the hurd. The bast part of the hemp plant is woven into fiber. The hurd is often used for insulation, animal bedding and the many other uses that do not require a long fiber length.
Growing Season, Harvest — Seed
Hemp for seed is a full season crop. Hemp seed should be harvested when shattering begins. The rest of the plant will still be green and about 70% of the seed will be mature.
Water content may be as high as 22% to 30%, but is normally in the 18% to 20% range. Lower moisture risks the plant dropping seed.
Regular grain combines can be used for harvest and some have suggested settings similar to grain sorghum. Plants are cut just below the seed heads and the rest of the plant can be left in the field to harvest later for fiber, even as late as the following spring.
Hemp seed is thin-walled and fragile, requiring care in harvest, storage and transport. Grain should be dried immediately after harvest to less than 10% moisture.
Growing Season, Harvest — CBD
CBD hemp plants are normally grown from seed in greenhouses and then transplanted as “starts” in the field. Growing season is normally in the 100-120 day range.
These plants require much less density of plants per acre, significant clear-air space around the plants and continual removal of weeds via non-chemical methods.
Fields must be monitored to eliminate male plants as pollination of the desired female plants may increase THC levels and ruin the crop. Pull the male plants and get them out of the field. This is the most labor-intensive type of hemp production, surpassing even tobacco.