Cannabis is the Latin genus name for plants that include hemp and marijuana. This is very similar to Canis, the Latin genus name for dogs. Just as there are tremendous differences between Chihuahuas and Great Danes, so are there great differences in the genus Cannabis. These differences are due in part to the efforts of breeders emphasizing different traits that they desire in either the Cannabis plant or the dog. Hemp was bred from Cannabis to create not only tall sturdy plants for rope and fiber, but also hearty seeds for feed and oil. Marijuana was bred from Cannabis for its production of cannabinoids, the best known of which is THC, which causes the famous marijuana ‘high’. Cannabis produces over 60 other types of cannabinoids, many of which are reputed to have unique pharmacological properties. All Cannabis plants produce THC; however, marijuana marketed for medicinal or recreational purposes contains high levels of THC (over 10%), and hemp contains very little (0.3%).
Types of Hemp: Industrial hemp is composed of four types: Oilseed/grain, fiber, hybrid (dual purpose), which produces both fiber and seed, but not to the yield or quality of single-purpose cultivars, and for cannabinoids/essential oils (i.e. CBD hemp). When considering which cultivars or strains you want to work with, please consider the way these genetics have tested in regards to THC production. Please refer to the testing results from 2019 in the link below. This is only one field season’s worth of data, however, it is a good place to start when considering what genetics you may want to work with (or avoid). Hemp THC Results by Variety_update
Seed Labels: All hemp seed sold within Indiana will be required to have a proper seed label and seed sellers must have a seed permit with OISC. Hemp seed has been sold without proper labels in the past, and often times magic marker or small printed labels have been the “seed label”. This is not acceptable. To learn more about seed labels and see an example of everything that should be included, please see How To Label Hemp Seeds.
Hemp Growth and Development
- Hemp is a short-day plant. Short-day plants develop flowers only when the day length is less than 14-12 hours depending on the cultivar. For best results in Indiana, earlier planting will promote greater vegetative growth resulting in more robust plants for seed, and taller plants with higher fiber yields. However, extremely early planting for grain specific hemp may make harvest difficult depending on how high your combine head can go. Days begin to get shorter after June 21st, and approximately four to five weeks after this date, vegetative growth slows and flower development is triggered. We have seen flowering begin much early though, sometimes two to three weeks after June 21st. Just like we have soybeans for specific latitudes, we will also need to see hemp for specific latitudes to maximize yields.
- Hemp is dioecious, meaning plants can be male or female. Differences between male and female plants in growth rate and development are large (Van der Werf and Van den Berg, 1995). Male plants tend to flower and senesce (die) earlier. To minimize the impact of this on production, many cultivars are bred to be monoecious, resulting in plants that are mostly females with male flowers (a small percentage of males plants are included for pollination), to harvest more seed (since male plants do not set seed) and for greater fiber production (since male plants die after flowering).
- Soil: One common myth is that hemp can be grown anywhere. Hemp grows best on a loose, well-aerated loam soil with high fertility and abundant organic matter, with a pH of 6.0-7.5. Well-drained or tiled clay soils can be used, but poorly-drained clay or poorly structured soils often results in establishment failures, as seedlings and young plants are prone to damping-off. Sandy soils can grow good hemp with adequate irrigation and fertilization but these additional costs often make production more expensive.
- Fertility: Another myth regarding hemp production is that it doesn’t require additional nitrogen or potash inputs: Hemp production requires inputs of up to 100- 130 lb of nitrogen/ acre, 45-70 lb/acre phosphorus, and 35-80 lb/acre of potash, as well as 10-15 lb/acre of sulfur. Canadian researchers have found hemp can pull a lot of nutrients out of the soil, specifically, 178 lb/ac N, 42 lb/ac P, 188 lb/ac K, and 12 lb/ac S. Phosphorus levels should be medium to high (>40 ppm) and calcium not in excess (<6,000 ppm). In addition to well-aerated, loamy soils, hemp does best when organic matter is greater than 3.5%. To provide perspective–hemp requires about the same fertility inputs as a high-yielding crop of wheat. Avoid seed place salt-based fertilizer, it can damage the seeds and could delay or prevent emergence. Fertility programs are not well developed for hemp, but growers will still want to consider the 4Rs, right rate, right source, right placement, and right timing. Many growers opt to get a soil test before and after they produce hemp to better understand how heavy of a nutrient user this crop is.
- Planting Date: Although the seedlings will germinate and survive at temperatures just above freezing, soil temperatures of 46°–50°F are preferable. Generally, hemp should be planted after danger of hard freezes, and slightly before the planting date of corn. Good soil moisture is necessary for seed germination, and plenty of rainfall is needed for good growth, especially during the first six weeks, for establishment. Rainfall should be about 25-30 inches per year but is most important in the first six weeks. This does not mean hemp seeds and seedlings can tolerate torrential downpours. This crop does not like wet feet.
- Planting Depth: Seedbed preparation requires considerable effort. Fall plowing is recommended, followed by careful preparation of a seedbed in the spring. The seedbed should be fine, level, and firm. Seed is best planted at 0.50-1.00 in (although deeper plantings may be tolerated, they are more susceptible to damping-off).
- Planting Density: The seeding rate is specific to the type of hemp and may even differ for each variety. This information should be sought from the supplier. Grain and fiber hemp is normally planted using a standard grain drill. Both grain/seed and fiber hemp is typically planted in 6-7-in. rows, using every run of the drill. Hemp planted for cannabinoid production is typically set using transplanting equipment. When hemp is planted on well-drained, fertile loam with appropriate temperature and moisture conditions, seed will germinate quickly and reach 12 inches in 3-4 weeks from planting. At this stage, it will give 90% ground shade and suppress the growth of weeds by shading. Rapidly growing hemp at a density of approximately 20 plants/sq ft, will suppress nearly all weed growth.
- Hemp Rotations: Hemp can be grown in continuous rotation for several years on the same land. However, the risk of pest buildup, particularly root pests, borers, and rots, makes this a risky proposition. Hemp also pulls a lot of nitrogen and potassium out of the soil (figure from Canada. Hemp is being used to diversify current rotations of beans, wheat, or alfalfa. Based upon reports from Ontario, Canada, it has been recommended that hemp not follow canola, edible beans, soybeans or sunflowers due to the risk of white mold and other pests and diseases. This would be location specific though. Not all areas of the country will have a high incidence of white mold. Rotation recommendations will have to be developed for different regions of the country and even different regions within a state. Previous crops planted and what crops are near fields will become even more important as we identify more pests and diseases of hemp.
Few pesticides (insecticides, herbicides, or fungicides) are registered for use on hemp in the United States. There are Section 3, 25(b), and 24(c) products available for use in Indiana. Only certain 25(b) products are registered for use on hemp in Indiana (and other states). These products have ingredients that have been deemed a minimum risk by the EPA. Efficacy of products has not been evaluated in hemp and growers should follow the label directions carefully to achieve the best results. For now, crop rotation is a good management option available to avoid disease build-up until more is known about hemp’s susceptibility to disease organisms and fungicide efficacy has been evaluated. Do not grow hemp on the same fields following canola, edible beans, soybeans or sunflowers if you have struggled with white mold in the past. More info on insects, mites, pathogens, and weeds can be found under the “Pests” tab.
Hemp is now a listed crop on drift watch.
Baxter, J. 2000. Growing Industrial Hemp in Ontario. Agdex# 153/20. Available at http://www.omafra.gov.on.ca/english/crops/facts/00-067.htm#fertility
Van der Werf, H.M.G. and W. Van den Berg. 1995. Nitrogen fertilization and sex expression affect size variability of fibre hemp (Cannabis sativa L.) Oecologia, 103: 462–470
Small, E. and D. Marcus. 2002. Hemp: A new crop with new uses for North America. p. 284–326. In: J. Janick and A. Whipkey (eds.), Trends in new crops and new uses. ASHS Press, Alexandria, VA.