Industrial hempFrequently Asked Questions

The following are commonly asked questions regarding hemp production and analysis, along with answers and helpful resources to assist your hemp growing and processing needs.

1. What certifications does your hemp analysis have?

There is currently no certification program through DATCP or any other agency for hemp analysis in Wisconsin. Our lab does participate in proficiency testing programs administered by the University of Kentucky and Emerald Scientific to ensure that our analyses are top quality. Outside of hemp testing, Rock River Lab maintains certifications through several agencies and participates in many proficiency testing programs.

2. How do I fertilize hemp?

The following resources can assist in learning more about fertiilzing hemp: 

Nitrogen uptake by the hemp plant is the strongest during the first six to eight weeks of growth. Potassium and phosphorus become critical during later stages of development with the onset of both flowers and seed. Manure applications will likely be beneficial (Kraenzel et al. 1998)

Although nitrogen needs and applications vary between hemp cultivars, nitrogen additions have been shown to be more beneficial than both phosphorus and potassium applications at increasing plant biomass (Vera et al. 2004, 2010). Information from the hemp seed supplier will be critical when determining a nitrogen application rate.

3. Should I grow hemp from seed or should I buy clones?

This question is most relevant to CBD hemp growers as hemp grown for grain or fiber is grown from seed. Here are a few considerations for CBD hemp growers: 

  • Access to clones: The Wisconsin Department of Agriculture, Trade Consumer Protection (DATCP) has compiled a list of licensed seed and clone providers here: There are far more seed providers than clone providers. Use of clones will be limited to growers who have a clone seller within a realistic distance from their operation.
  • Sexing the plants: One of the main advantages of planting clones is a guarantee of only female plants in the production area. Sexed seed is available, but is not 100 percent guaranteed to be female only.
  • Cost: Generally speaking, seed will be less expensive than clones, but will require more labor for elimination of male plants.

The resource "Propagating Hemp for CBD" from Christine Motyka of the Vermont Technical College may be of assistance in learning more about beginning a hemp crop:

4. How do I plant hemp?

Industrial hemp is normally planted using a standard grain drill. Both oil and fiber hemp is typically planted in six to seven inch rows, using every run of the drill. Seeding rate is specific to each variety, and this information should be sought from the supplier. Seed is best planted at 0.75-1.25 inch spacing. Learn more here:

  • If growing for fiber, closer seed density (up to 726,000 plants per acre) encourages less branching and a longer main stem (Kraenzel et al. 1998).

  • If growing for seed, increasing both row and seed spacing will increase seed production row spacing can be adjusted up to 16 inches after which plant foliage will no longer provide sufficient ground shadow (Bocsa et al. 1998; Kraenzel et al. 1998)

  • Generally, germination occurs within 24 to 48 hours, and under optimum conditions plants will emerge in five to seven days (Kraenzel et al. 1998).

  • Soil temperatures ranging from 42 to 54 degrees Fahrenheit have been shown to have successful germination although soil temperature >50 Fahrenheit is recommended (Kraenzel et al. 1998; Ranalli 1999).

5. Where do I source hemp seed?

The Wisconsin Department of Agriculture, Trade, and Consumer Protection (DATCP) has compiled a list of companies that are licensed in Wisconsin to sell hemp seed here:

6. What is the difference between certified hemp seed and non-certified hemp seed?

Certified hemp seed is seed that has been professionally grown and has been verified for varietal purity and seed quality by a third party. In Wisconsin, the certifying party is the Wisconsin Crop Improvement Association. Learn more about certified seed here:

According to the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP), it is highly recommended that growers plant certified seed. Certified seed is more likely to produce a crop that meets the legal THC limit, and planting certified seed will protect growers from prosecution by the State of Wisconsin if the crop exceeds the THC limit. Non-certified hemp seed can come from various sources and be of varying quality, but the main difference is that it has not been verified for varietal purity and seed quality by a third party. Wisconsin DATCP's industrial seed and transplant information can be found here:

7. Where do I source hemp clones?

The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) has compiled a list of companies that are licensed in Wisconsin to sell hemp clones. Learn more here:

8. How can I tell if my hemp crop is getting hot (Delta 9-THC’s concentration is approaching levels above the legal limits)?

Analyze the crop. The equipment utilized for this analysis is called HPLC (high-performance liquid chromatography).  Prior to harvest, growers MUST have their crop sampled and tested by the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) to ensure it is below the 0.3% THC requirement. Depending on the Wisconsin DATCP test results, the grower then has ten days to either harvest, retest, or destroy the crop. Currently, the Wisconsin DATCP does not certify labs for time of harvest testing. Pre- and post harvest testing can be provided by Rock River Laboratory to monitor the progress of THC and other cannabinoids through the growing season with the Cannabinoid Profile. This analysis reports concentrations of CBC, CBD, CBG, CBDA, CBGA, CBDV, DBDVA, Delta-9 THC, Delta-8 THC, THCA-A, and THCV, as well as the moisture level. Learn more about this profile here

Learn more about the Wisconsin DATCP harvest analysis here:

9. What do I do if my hemp crop looks sick?

Hemp is susceptible to many of the same pests and diseases as other commonly grown agricultural crops. In comparison to corn or soybeans, the diagnostic tools for hemp crop troubleshooting are very limited. Standard resources for crop diagnostic troubleshooting such as University of Wisconsin (UW) Extension Agents and Certified Crop Advisors may not have experience with hemp. The UW Extension Hemp Team has started a directory to help those in hemp industry make connections. Learn more here:

The University of Wisconsin Plant Disease Diagnostic Clinic offers hemp disease identification services. See their website for sample collection, submission, and fee information.

The International Hemp Association has also compiled articles on hemp diseases and insect pests. Learn more at the links below:

Nutrient deficiencies can be diagnosed by visual inspection of the plant, and confirmed through tissue testing. Rock River Laboratory offers both plant tissue testing and plant tissue plus soil analysis testing to create a comprehensive view of the soil and plant nutrient relationship, to assist in diagnosing such deficiencies. Learn more about these analysis here

10. How do I pull a hemp plant tissue sample for nutrient analysis? 

Collect the newest, fully developed leaf from at least 30 plants in the problem area. It’s important to collect a sample that’s representative of the area of concern.

If there is a good area as well as a bad area, it’s a good idea to collect samples from both. This will allow for a comparison between the good and poor crop. That’s especially important in hemp, as there is little information on plant tissue interpretation. 

11. How and when can I sample my hemp for potentcy?

Rock River Laboratory's recommended timing is to begin samling two weeks post flowering, and continue sampling weekly until harvest.

Typically, growers will sample weekly from flower emergence up until harvest, in order to review their crops potency.

12. How do I pull a soil sample?

For a uniform fertilizer recommendation, soil samples should be taken at a rate of one sample per five acres.  Each composite sample should be made up of at least ten cores that are taken throughout the field in a “W” shaped pattern.  Sample cores should be taken from the depth of tillage, and should be taken at a consistent depth for each core. Areas of the field that may have fertility levels that do not represent the field (i.e. eroded knolls and headlands) should be avoided. See the University of Wisconsin (UW) Extention Publication A2100 for more information on proper sampling procedure:

13. I want to create a nutrient map of my field but I don’t have the equipment to do so. What are my options? 

Rock River Laboratory has a full staff of soil scientists ready to help map the nutrients in your fields. Call us at 920-261-0446 for more information.

14. How do I tell if there are pesticides in my soil?

Accounting for residual pesticides in soil is crucial for ensuring the health of your future hemp crop. The first thing to consider in regards to residual pesticides is what chemicals were applied in the previous growing season. There are three factors that determine the persistence of a herbicide, or how long it will remain in the soil. Chemical properties, soil factors, and environmental factors all impact the persistence. A good starting point for determining whether or not you have remaining herbicide activity is the chemical label. It will give information on the chemical properties and replant restrictions. If you are unsure, having the soil tested is the only way to be certain there are no remaining chemicals that could be harmful to your hemp crop (or any herbicide sensitive crop for that matter). Rock River Laboratory offers a 17-pesticide screen, regulated by the Wisconsin Department of Agriculture and Consumer Protection (DATCP) that can help with this very need. Learn more here.

Additional information regarding the three factors affecting herbicide resistance can be found at

15. How do I harvest my hemp crop?

The Cornell University resource, "Industrial Hemp from Seed to Market" can assist in learning more about harvesting hemp. Page 4 of this resource linked below provides information for grain and fiber varieties, as well as citations with additional helpful information:

The resource 'Industrial Hemp Harvest and Storage" can provide additional harvesting information:$department/deptdocs.nsf/all/crop15539/$file/HempHarvestStorage.pdf?OpenElement

Harvest for all hemp end uses is very different.  Hemp grown for grain is harvested when the grain is mature and grain moisture content has reached a desired level.  Harvesting is done with a conventional combine. Hemp fiber is at the highest quality around the time of pollination, so it is generally harvested much earlier than hemp grown for grain.  Hemp for fiber is mowed and baled at 15% moisture. Hemp grown for CBD is grown to near maturity. The whole plant is cut by hand and hung to dry to processors specifications. Learn more here:

Although a conventional combine will work for hemp harvesting it is recommended that models with a modern rotary design be implemented. Increased clearances on more modern equipment will reduce the chance of wrapping around the rotor during harvest, it is also worth noting that Canadian growers prefer a draper header instead of the conventional auger header (CHTA 2019).  

16. How do I dry hemp?

Drying procedures will vary by the intended end use.

CBD use: Hemp plants are usually harvested by hand by cutting the plant at the base of the main stalk. After harvest, the hemp plants should be brought to the drying facility as soon as possible. Drying facilities should be under roof, protect the plant from the sun, and well ventilated. Ideal drying conditions are 60-70 degrees F at 60% humidity. Ventilation is key, and fans should be employed for continuous air movement. The plant should be hung upside down with adequate distance from other plants to ensure adequate air flow. Learn more here:

Grain use: Hemp is usually combined at 10-20% moisture.  According to a Canadian source, the industry standard for dry storable grain is 10% moisture.  Grain quality can be greatly diminished by excess heat during the drying process, so special attention should be given to drying temperature.  Grain above 13-14% moisture should be dried in a grain dryer, while grain with lower moisture content can be dried effectively in a properly aerated grain bin. Learn more here:

Fiber use: Post-harvest management of hemp grown for fiber can vary greatly depending upon the end use of the fiber.  In general, the stalks are dried in the field and baled. Hemp fiber is considered stable for storage at 12-16% moisture.  Hemp stalks grown for fiber must undergo a process called “retting” where the inner part of the stalk is separated from the outer part of the stalk.  Retting can be accomplished through biological or chemical means. Biological retting is accomplished by leaving the stalks in the field so that microorganisms can accomplish the separation. Learn more here:$department/deptdocs.nsf/all/crop15539/$file/HempHarvestStorage.pdf?OpenElement

17. What pesticides can I use on my hemp crop?

All pesticides used on a commercially grown crop must be used in strict accordance with rules and restrictions listed on the pesticide label.  Since hemp is a relatively new crop and the pesticide labeling process is lengthy and expensive, few commonly used agronomic pesticides are allowed in hemp production.  Many of the pesticides that are allowed are organic pesticides that are generally considered safe for all crops. The Wisconsin Department of Agriculture, Trade, and Consumer Protection has compiled a list of pesticides that are allowed for use on hemp:

18. Can I use herbicides on my hemp crop? 

There are currently no synthetic herbicides labeled for either “pre” or “post” application in hemp.  Weed control can be achieved through cultural methods (i.e. row spacing to encourage rapid canopy closure) or mechanical methods (i.e. in season cultivation).  When hemp is grown in rotation with conventional agronomic crops, careful attention should be paid to herbicide carryover from preceding crops. University of Wisconsin (UW) Extension weed scientists are researching carryover risk and have compiled a guide for growers:

19. What do I need to do differently based on what my hemp crop is intended for (oil, grain, fiber)?

Considerations for different hemp crop end uses fall into two main categories: genetics and management.

Genetics: Just as you wouldn’t plant a sweet corn variety if the intended crop is yellow No. 2 corn, careful consideration of the intended end use should be made when selecting a hemp variety.  While some hemp varieties are considered dual purpose for fiber and grain, varieties grown for CBD production will be in a category of their own. 

Management: The major distinction is between hemp grown for grain/ fiber and hemp grown for CBD.  Hemp grown for grain/ fiber is managed broadly similar to other grain and fiber crops. Planting and harvesting is generally done mechanically.  Fiber and grain varieties will be grown at much higher plant populations than for CBD production. Hemp grown for CBD is generally more labor and management intensive. One of the major differences in CBD production is the exclusion of male plants from the CBD hemp production area.  This management practice is done to prevent pollination of female plants by male pollen. If a female hemp plant is pollinated, the plant’s energy will shift towards seed production and away from CBD production. Hemp grown for CBD is planted at a low seeding rate to encourage a bushy growth pattern and increased flower production.

The Wisconsin Department if Agriculture, Trade, and Consumer Protection (DATCP) has compiled an overview of management practices and considerations for different hemp crop end uses here:

20. Where can I find industry groups for more information? [Rock River Laboratory does not endorse these industry groups.]

Wisconsin Hemp Alliance:

  • The Wisconsin Hemp Alliance is an association of hemp seed and clone suppliers, growers, processors, retailers, and consumers engaging in advocacy, education, and promotion of hemp and hemp products. The WHA is solely focused on non-psychoactive industrial hemp products.

Wisconsin Hemp Farmers & Manufacturers Association

  • “Our non-profit association was founded with the intention to aid the growth of Wisconsin’s hemp industry in all areas. Through education and with a little dirt under our nails, we work directly with our farmers to ensure they yield the best possible crop for processors. We teach sustainable farming practices with a zero waste approach! We provide our farmers and manufacturers free networking, all the way from the farms to supplier’s shelves, through our established relationships with processors and suppliers and our commitment to cultivating community. In partnership with Wisconsin Lobbyists, we advocate on behalf of Wisconsin farmers and manufacturers to reform existing laws.”

Hemp Industries Association

  • The mission of the Hemp Industries Association (HIA), a 501(c)(6) membership-based non-profit trade association, is to advance the hemp economy and educate the market for the benefit of our members, the public, and the planet. 
  • Activities Include:
    • “Educate the public about the exceptional attributes of hemp products.”
    • “Facilitate the exchange of information and technology between hemp agriculturists, processors, manufacturers, distributors and retailers.”
    • “Maintain and defend the integrity of hemp products.”
    • “Advocate and support socially responsible and environmentally sound business practices.”

National Hemp Association

  • Mission: To support the growth and development of all aspects of the industrial hemp industry.
  • Activities include:
    • “Educating and informing the public about the health, environmental, and economic benefits of reviving an industry that has been prohibited for over seventy years;”
    • “Building a community of individuals, businesses and organizations to facilitate the growth of the industry;”
    • “Working collaboratively with industry, government officials, and the scientific community to create and implement industrial hemp standards, certifications and regulations.”


Bocsa Ivan, Karus Michael, Hemptech (Firm) (1998) The cultivation of hemp : botany, varieties, and harvesting.

CHTA (2019) Hemp Production eGuide » Harvest Equipment. In: Hemp Production eGuide » Harvest Equipment. Accessed 12 Jun 2019

Kraenzel DG, Petry TA, Nelson B, et al (1998) Industrial hemp as an alternative crop in North Dakota

Ranalli Paolo (1999) Advances in hemp research. Food Products Press, New York. Book sections available:

Vera CL, Malhi SS, Phelps SM, et al (2010) N, P, and S fertilization effects on industrial hemp in Saskatchewan. Can J Plant Sci 90:179–184. doi: 10.4141/CJPS09101

Vera CL, Malhi SS, Raney JP, Wang ZH (2004) The effect of N and P fertilization on growth, seed yield and quality of industrial hemp in the Parkland region of Saskatchewan. Can J Plant Sci 84:939–947. doi: 10.4141/P04-022