Friday, January 13, 2017


Hemp offers abundant opportunities for growers of all sizes along with a long list of product possibilities. Some see hemp as the plant of the future.  It is important to understand this is a living organism that humans will cultivate. 
The energy and resource needs of cultivation, especially on an industrial agricultural scale, are important to understanding.  How will hemp fit into a world with diminishing, easily available fossil fuels?  How will hemp fit into a world where basic resources are becoming less concentrated and more energy demanding?

Often, in the heat of enthusiam, the energy and resource requirements of a product are overlooked.  It is also important that the equipment in the field and in the manufacturing of the various products not become invisible. 

I have divided this essay into two parts, two entries.  The first part is extracts from multiple sources on cultivation mainly in the field.  The second essay is primarily videos of cultivation and the making of products.  I have found videos to be a productive way to reveal the machines, buildings and equipment required.

A lot of effort was put into looking for the energy requirements for both field work and for the manufacturing of products.  I have contacted researchers studying/working with hemp.  I have had very little success finding explicit energy information.  The charts included from the one source I found do not give clear information on the energy used in various operations.  If anyone knows of other energy assessments, please comment.  Perhaps, this will be the next phase in the study of hemp.


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 soil often results in establishment failures, as seedling 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 uneconomical.

Industrial hemp can be grown on a wide variety of soil types. Hemp prefers a sufficiently deep, well-aerated soil with a pH of 6 or greater, along with good moisture and nutrient holding capacity. Poorly drained soils, however, are not recommended as excess surface water after heavy rains can result in damage to the hemp crop. Hemp is extremely sensitive to flooding and soil compaction.


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 (to keep potassium levels in a medium to high range of >250 ppm). Hemp particularly requires good nitrogen fertilization, more so for seed production than fiber.  .  .  .  .
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, or corn.

Approximately 42% of the plant’s biomass returns to the soil in the form of leaves, roots and tops. These contain over half of the nutrients applied to the crop in the first place and many of these nutrients will be available to help feed the following crop.

To achieve an optimum hemp yield, twice as much nutrient must be available to the crop as will finally be removed from the soil at harvest. A hemp field produces a very large bulk of plant material in a short vegetative period. The nitrogen uptake is most intensive the first 6 to 8 weeks, while potassium and in particular phosphorous are needed more during flowering and seed formation. Industrial hemp requires 80 to 100 lbs/ac (90 to 112 kg/ha) nitrogen, 35 to 50 lbs/ac (39 to 56 kg/ha) phosphate and 52 to 70 lbs/ac (60 to 80 kg/ha) potash.Growing  Conditions:Hemp prefers a mild climate, humid atmosphere, and a rainfall of at least 25-30 inches per year. Good soil moisture is required for seed germination and until the young plants are well established.

Hemp Rotations: Hemp can be successfully grown in continuous rotation for several years on the same land. However, the risk of pest buildup, particularly root worms, borers, and rots, makes this a risky proposition. Hemp could be used to diversify current rotations of bean, 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.

Weed Control:
Industrial hemp is an extremely efficient weed suppressor. No chemicals are needed for growing this crop. Industrial hemp is a low maintenance crop. There are no registered chemicals for weed control in hemp. A normal stand of 200 to 300 plants per square meter shades out the weeds, leaving the fields weed-free at harvest.

Pest Management. Like most plants, hemp is prone to insects and pathogens. As the acreage of industrial hemp increases, the number of insect pests and pathogens will tend to increase, as well.

Disease. Historically, the fungal pathogens gray mold (Botrytis cinerea) and white mold (Sclerotinia sclerotiorum) have been reported to infect and impact industrial hemp production. In Indiana, white mold in particular, is expected to be a major pest north of highway 70, particularly when soybeans are grown in adjacent locales, or in rotation with hemp. Hemp is also prone to numerous fungal and bacterial leaf spots, viruses, and Pythium root rot and blight during establishment.

Insects. European corn borer, armyworm and grasshoppers have done some damage to hemp crops in North America.
No pesticides (insecticides, herbicides or fungicides) are registered for use on hemp in the United States. 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 4-year rotation is recommended. Do not grow hemp on the same fields following canola, edible beans, soybeans or sunflowers.


The first thing to consider is:  what will be the end use of this hemp?  If you are looking to harvest seeds, you will need different equipment and hemp varieties than if you are looking to harvest stalks for fiber.  It turns out that the optimum time to harvest hemp for fiber is well before the optimum time to harvest hemp for seeds.  So it is probably best to decide on one goal or the other before you plant a field.  It is possible to harvest both seeds and stalks, however.

If harvesting hemp for fiber on a smaller plot, a well-maintained sickle-bar mower or hay swather may be used to cut the stalks.  The stalks are cut and left in the field and allowed to rot slightly to begin separating the fibers from the stalk.  This process is called “retting”.  After retting, a baler may be used to bale the hemp stalks, at which point the stalks are ready for storage, drying, and sale.

If harvesting hemp for seed, a combine may be used, although this can be a challenge.  It is recommended to raise the blade a meter or higher, but even then the long fibers of the hemp plant can cause wear and tear on the machine by winding through moving parts.

Harvesting Fibre Hemp
Air dry stem yields in Ontario have ranged from 2.6-14.0 tonnes of dry, retted stalks per hectare (1-5.5 t/ac) at 12% moisture. Yields in Kent County have averaged 8.75 t/ha (3.5 t/ac). Northern Ontario crops averaged 6.1 t/ha (2.5 t/ac) in 1998. Researchers feel earlier planting, optimum production management and more suitably adapted varieties can result in higher yields.
Approximately one tonne of bast fibre and 2-3 tonnes of core material can be decorticated from 3-4 tonnes of good quality, dry retted straw.

Fiber hemp is ready to harvest about the time the plant is finished producing pollen and the first seeds start to develop. However, this does vary with the variety and maturity of the fiber desired. If left beyond this stage, the fiber becomes too coarse. Fiber from the male plant dies soon after pollination. It is coarse and good for fiberboard and other products since it is stronger than younger fiber.
Because hemp is sensitive to light, early planting will produce taller crops and thus more fiber. Stems must not be chopped or broken too much in the harvesting process since long fibers are more desirable.

Chemical Defoliation
Removing the leaves from hemp by hand is virtually out of the question. . .  .  .  .   Therefore, many farmers resort to chemical defoliation.  .  .  .  .  . 
Chemical Defoliants
Roundup is one chemical defoliant. .  .  .  .  .  . Purivel is a supposedly gentler chemical that contains the active substance Metoxuron (by Sandoz).  .  .  .  .  .  Basta .  .  .  . is toxic to fish and may be used only on fields from which the flow-time is at least 50 days to the next water treatment facility.
Alternatives to Chemical Defoliation
Ecologically-minded textile manufactures in western Europe are no longer accepting goods that have been subjected to chemical defoliation. .  .  .  .  Alternatives include labor-intensive manual removal of the leaves, mechanical removal (but new machines need to be invented), or water-retting without defoliation. All have disadvantages. Newer methods developed in the west do not require chemical defoliation since they no longer employ water retting.

Once the hemp is harvested, it must go through a process called retting in order to separate the fiber from the rest of the plant. This is not an easy process and can be accomplished through several methods where moisture, microorganisms, or chemistry break down the bark tissue that binds the fiber and non-fiber portions, making them easier to separate.
Dew retting occurs when the stalks are left in the field so that rain, dew, or irrigation is used to keep the stems moist. This may take up to 5 weeks and produces a coarse fiber with a light brown color.
Water retting occurs when stems are bundled and then submerged in water so that bacteria break down the pectin. This takes 7-10 days and produces a better quality fiber.
Warm water retting occurs when bundles are soaked for 24 hours after which the water is replaced. Heat is then applied to warm the batch for the next two or three days. This gives a very uniform, clean fiber.
Green retting is an all mechanical process that separates the components and used when the fiber is needed for textiles, paper, or fiberboard products.

Green Retting Machines

Energy balance
Energy input
The four base scenarios differed substantially in their relative amount of energy
input (Figure 18). The energy input in cultivation was found to be 10.8 and
10.4 GJ ha-1 for baled and briquetted solid biofuel production from spring 
harvested hemp, respectively, and 7.4 GJ ha-1 for autumn-harvested, ensiled 
hemp biomass for biogas production (Figure 18; Paper IV).

After intermediate storage, processing of the stored biomass requires energy
inputs for conversion and additional transport. Conversion energy requirements
differed substantially between the scenarios: inputs were low for solid biofuel
combustion in the form of briquetted biomass (0.8 GJ ha-1) and for CHP
production from bales (1.5 GJ ha-1) (Figure 18). CHP production from biogas
was more energy-intensive (2.8 GJ ha-1). The most energy-demanding
conversion was the production of vehicle fuel (14.1 GJ ha-1), where upgrading
of the biogas to 97% methane content represented 45% of the total energy
input. This reflects in the high amount of electricity required for scrubbing and

compression of the biogas (Figure 18).

One gigajoule equals almost 7 gallons of diesel fuel
One gigajoule equals almost 7.5 gallons of gasoline.
One hectare equals 2.47 acres

Energy output
For CHP production from solid biofuel, approx. 23 and 41% of the energy contained in the biomass in the field was made available as useful power and heat, respectively (Scenario I, Figure 19). Heat production from hemp briquettes resulted in approx. 55% of the energy being made available as useful heat (Scenario II, Figure 19).

The production of 1 ha of hemp .  .  .  an energy use of 11.4 GJ, and a land use of 1.02 ha.year.

One gigajoule equals almost 7 gallons of diesel fuel
One gigajoule equals almost 7.5 gallons of gasoline.
One hectare equals 2.47 acres

Net energy yield
The net energy yield (NEY) per hectare was highest for CHP production from
bales and heat from briquettes with 81 and 65 GJ ha-1, respectively (Figure 21; Paper IV). Overall, conversion efficiencies for these pathways were high (86 and 80%, respectively) as were the output-to-input ratios (RO/I of 6.8 and 5.1, respectively). The NEY of biogas CHP and vehicle fuel production was
substantially lower, 24 and 42 GJ ha-1, respectively. Conversion efficiency was
38% for upgraded biogas (vehicle fuel) and 21% for biogas CHP. Both scenarios had RO/I = 2.6.


Hemp has been described as a carbon sink. It takes up vast amounts of carbon during its rapid growth and this can be locked up in durable products. Hemp’s bio-remedial qualities enable it to improve soil structure and mop up toxic wastes including heavy metals and excess nutrient. Planted densely it achieves weed suppression and doesn’t require pesticides or fungicides. It is also exceptionally good in the farm nutrient cycle as a rotation crop.

A supporting but stricter view:
Although the environmental and biodiversity benefits of growing hemp have been greatly exaggerated in the popular press, C. sativa is nevertheless exceptionally suitable for organic agriculture, and is remarkably less “ecotoxic” in comparison to most other crops (Montford and Small 1999b).

Cannabis sativa is also relatively resistant to weeds, and so usually requires relatively little herbicide. Fields intended for hemp use are still frequently normally cleared of weeds using herbicides, but so long as hemp is thickly seeded (as is always done when hemp is grown for fiber), the rapidly developing young plants normally shade out competing weeds.

Most insects cause only limited damage to hemp, and substantial insect damage is uncommon, so the use of insecticides is very rarely required.

The most valid claims to environmental friendliness of hemp are with respect to agricultural biocides (pesticides, fungicides, herbicides). Cannabis sativa is known to be exceptionally resistant to pests (Fig. 51), although, the degree of immunity to attacking organisms has been greatly exaggerated, with several insects and fungi specializing on hemp. Despite this, use of pesticides and fungicides on hemp is usually unnecessary, although introduction of hemp to regions should be expected to generate local problems. Cannabis sativa is also relatively resistant to weeds, and so usually requires relatively little herbicide. Fields intended for hemp use are still frequently normally cleared of weeds using herbicides, but so long as hemp is thickly seeded (as is always done when hemp is grown for fiber), the rapidly developing young plants normally shade out competing weeds.


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.
This covers much of the issues and questions as well as a huge bibliography

How Hemp Textiles Are Produced

Russell, Jesse; Dalsted, Norman ; Tranel, Jeffrey E. and Young , R. Brent.   2015.  Industrial Hemp.

Baxter, J. 2000. Growing Industrial Hemp in Ontario.  Agdex# 153/20. Available at

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.

Small, E.  2016.  Cannabis, A Complete Guide.  CRC Press. FL.

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.

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