Industrial Hemp Agronomics

This article was first published on Dr. Shawn Conley’s Cool Bean website on February 7, 2018. A portion of the article has been archived here for your convenience.


Authors: Shawn P. Conley, John Gaska, Adam Roth, Cheryl Skjolaas, Erin Silva, Loretta Ortiz-Ribbing, William Barker, and Patrick Robinson



Besides work done in the early 20th century, there is little information on growing hemp in Wisconsin that is based on local research. The following information is gleaned from these references:

Purdue University Hemp
Kentucky Hemp Production
Cornell University Hemp
Canadian Hemp Trade Association Production eGuide
Finola oilseed hemp

When do you plant hemp?
Based on work done in neighboring states, planting done from mid-May to late-June resulted in highest yields with lower risk of frost injury.

What is the seeding rate?
General seeding recommendations is between 20-40 lbs per acre for grain production, and 40-60 lbs per acre for fiber production. A lot of factors go into determining the optimal seeding rate for your field, including the variety, seed purity and germ, local conditions, etc.

The end use of your hemp crop will dictate the seeding rate. When growing hemp for fiber only production, it is suggested the seeding rate should be double what is used for grain production. The reason for higher seeding rates is to ensure a higher quality fiber crop. Good quality hemp fiber comes from plants that are “pencil thin”. Higher seeding rates will ensure that there will be a high plant population with tall thin plants with longer internodes. Research is limited in Canada to determine proper seeding rates to achieve high yielding and good quality fiber. Low plant populations will not provide competition for early weed control. Hemp can have a high mortality rate under adverse growing conditions. Research has shown that 10% to 70% seed mortality can occur under varied climatic conditions. Based on observations, reasons for high mortality are generally attributed to:

  • Poor growing conditions at seeding
  • Seeding too deep
  • Cracking of the seed coat
  • Toxicity from high rates of seed placed fertilizer
  • Residual herbicides from previous crop

What are some seeding recommendations?

Most conventional drills and seeders will work for hemp. To enhance hemp plant stands:

  • Seed into warm soil
  • Seed into a firm seedbed with good soil to seed contact
  • Seed shallow, 1.25 cm (0.5 inches) to on 2.5 cm (1 inch) maximum
  • Do not seed deep into moisture in a dry year. In spite of being a moderately large seed, hemp will struggle to emerge from deep seeding
  • Avoid seeding before an abundance of precipitation is anticipated. Seed after a heavy rain rather than before
  • Although most seeding equipment will work for hemp it is important to monitor seeder output to avoid seed cracking. Cracking occurs in the manifolds when air volume is too high
  • Take into account germination rate. A common percentage of 70% germination is often used when calculating seeding rates. If spring seeding conditions are ideal this rate can be lowered
  • Avoid compaction from wheel tracks or other soil compaction, as with other crops, will show up under certain conditions
  • Avoid excessive trash that can keep soils cool and could cause hair pinning with disc drills

Can you plant hemp on hemp? How does it fit into a crop rotation?
According to the Canadian Hemp Trade Alliance (CHTA) “hemp fits in with typical crop rotation systems and with typical equipment that would already be found in a grain production system.”

Can I grow hemp organically?
Yes. On August 23, 2016, the National Organic Program (NOP) released this statement: “For hemp produced in the United States, only industrial hemp, produced in accordance with the 2014 Farm Bill, as articulated in the Statement of Principles on Industrial Hemp issued on August 12, 2016 by USDA, may be certified as organic, if produced in accordance with USDA organic regulations.” Some certification agencies will allow industrial hemp to be included in an organic rotation, so long as the growers are properly licensed under a pilot program. However, some certifiers may be taking a more hesitant approach, since there are many questions yet to be answered. Thus, farmers should talk to their certifier before making the decision to include this crop within their organic rotation. If growing industrial hemp, organic farmers will be required to do an organic seed search before using nonorganic seed.

Use practical organic farming practices such as a perennial clover or green manure plow down, with added manure to increase nutrient availability for rapid initial growth. Reduce any weed pressure by plowing and harrowing prior to sowing. The seedbed must be as fine and even as possible. Good soil, farming experience and proper nutrient levels are essential for successful organic oilseed hemp production.

Do you need to fertilize hemp?
Hemp has similar nutrient needs as canola and especially requires added nitrogen. Fertilize like rapeseed (Canola- Brassica napus) with 15% additional nitrogen. Conventional NPKS (nitrogen, phosphorus, potassium and sulfur) fertilization is recommended at the same levels required to grow rapeseed. Apply additional K and S wherever soils are deficient in these elements.

How/When do you harvest it?
Hemp can be grown for seed or fiber. Hemp grain harvesting is generally done by straight combining, however swathing is also used. Newer models of combines are best suited to handling hemp harvest and require minimal modifications. The new machines have bigger cylinders and cleaning area. In addition, newer combines can operate with headers at higher levels so all stands of hemp can be accommodated. Most new combines are now rotary design. Some new machines have the swath entering at the bottom of the cylinder. The draper header is preferred by growers.

The top third of the crop may be combined for grain while the plants are still “green” (70-90% seed head maturity). Harvesting while the crop is partially green will help minimize cutting and wrapping problems. The main disadvantage at harvest is plugging the combine with stems and other moist vegetative material. Dry field conditions are essential for a good harvest. However, a dead and desiccated crop will be more difficult to cut, more prone to wrapping and subsequent fire hazard. Grain moisture should be at least 10-15% at the time of harvest.

What kind of yield can I expect?
Yields can vary widely depending on the variety, local climatic conditions, cultivation method, and grower experience. For grain, new growers have reported yields between 250-700 lbs/acre. More experienced growers can expect between 800- 1,800+ lbs/acre. For fiber, the average yield for dual purpose crops (those varieties which are harvested for grain and fiber) is 0.75-2 tons/acre. For hemp produced solely for fiber, the average yield is between 3-5 tons per acre.

How deep are the roots?
Hemp has a large root capable of penetrating deep in the soil profile to recover nutrients that may be lost to many other crops, up to the 24-inch level.

What are some weed management strategies?
Given a good start, hemp can be an effective weed suppressant. Currently, there are no registered herbicides for weed control in hemp. A quick, even emergence is the key to effectively compete with weeds, by rapidly creating a dense leaf canopy within the first month of growth. Hemp will self thin to an optimal density, and it is better to have this crop compete with itself, rather than weeds. It is recommended to minimize weed pressure in the previous year and start with spring tilling and harrowing. Perennial forages or green manure plow downs are good preceding crops. Problem weeds may include wild buckwheat, wild oat, Amaranthus species, Chenopodium species, rapeseed, and other volunteer crops.

Where can I buy hemp seed from?
The Act requires DATCP to establish and administer an industrial hemp seed certification program, or designate a member of the Association of Official Seed Certifying Agencies or a successor organization to administer a seed certification program. This seed certification
program must include the testing and certification of THC concentrations in hemp plants. Participation in the certification program must be voluntary for growers and cultivators of industrial hemp. The Act also authorizes DATCP to seek federal approval to serve as an importer of industrial hemp seed. Importing seeds into Wisconsin to begin the hemp program may require permission from the U.S. DEA, which could affect the time when production can begin.

Other seed-related questions that may be addressed by the rules are:

  • Can I save seed for planting the following year?
  • Do I need a seed permit to sell hemp seed in Wisconsin?
  • Can I breed a new variety of hemp for Wisconsin?

Do I need a grain buyer’s license to buy hemp grain?
Yes, if you are buying hemp grain with the purpose of reselling the grain or products made from the grain. In addition to a license, a bond must be acquired.


  1. Hemp is sold as a raw food so avoiding contamination is extremely important.
  2. All harvest related equipment should be cleaned out prior to harvest to ensure no contamination occurs from other crop types that are difficult to clean out of hemp.
  3. Combine divergent crops like canola or soybeans before combining hemp. This cleans out the combine and these crops are easily removed if contamination occurs.
  4. Clean grain as soon as possible to maintain grain quality and ensure safe storage. Inspect trucks for cleanliness before loading clean grain that is destined for the processor.
  5. For maximum shelf life, grain should be stored in a clean, dry location. Storage temperatures in excess of 75° Fahrenheit for a sustained period of time may cause rancidity and separation of the soluble and insoluble proteins.


  1. Hemp is combined at a moisture content of 10 to 20% moisture. The majority of the moisture comes from broken plant material, immature seeds and seeds enclosed in bracts. Dockage will range from 10 to 20%. The wetter the sample, the more urgent the drying process is. Drying should begin within hours of harvest. Heated air grain dryers and aeration can be used for drying the seed down
  2. The industry has accepted 10% moisture as dry. A safer level is 8 or 9%. Percent moisture requirement should be checked with contractor.
  3. Hemp grain generally has a lot of bracts and broken plant parts that are higher in moisture than the grain. Once drying begins these plant parts dry quickly and the speed at which the grain dries also increases at the end of the drying cycle.
  4. Monitor grain dryer temperatures to ensure the seed and seed oil quality is not compromised. Overheating the seed can cause the seed to turn yellow and discount the oil quality.
  5. Use grain drying when seed moisture is over 13 or 14%
  6. Monitor the dryer operation closely. Batch and continuous flow dryers are the most commonly used. Augers should be run full and slow to prevent cracking of the grain.
  7. Use heat of 150 to 160 degrees F for the first ½ of the drying period and then use 120 to 130 degrees to finish off the drying.


  1. Cleaning is required to remove contaminants such as weed seeds, plant parts and insects and it should be conducted as soon as possible after harvest. More importantly, cleaning removes cracked seeds resulting from combining.
  2. When cracked seeds are exposed to the air it causes oxidized rancidity of the oil which will contaminate the other seeds in the seed lot. This gives the hemp seed an undesirable taste and shortens the shelf life.