This article focuses on cultivation and use of hemp (Cannabis sativa) as a source of oil, food, fibre, and other non-drug uses. For other meanings please see Hemp (disambiguation).
Hemp is a common name for Cannabis sativa and the name most used when this annual plant is grown for non-drug purposes. These include the industrial purposes for which cultivation licences may be issued in the European Union (EU). In the UK licences are issued by the Home Office under the 1971 Misuse of Drugs Act. When grown for industrial purposes hemp is called, often, industrial hemp, and a common product is fibre for use in a variety of different ways.
Hemp may be grown also for food (the seed) but in the UK at least (and probably in other EU countries) cultivation licences are not available for this purpose. Within Defra (the UK's Department for Environment, Food and Rural Affairs) hemp is treated as purely a non-food crop , despite the fact that seed can and does appear on the UK market as a perfectly legal food product.
Both the complete protein and the oils contained in hempseeds (rich in lanolin and linolenic acids) are in ideal ratios for human nutrition.
Until its rediscovery in the late 1980s, the use of hemp for fibre production had declined sharply over the past decades, but hemp still occupied an important place amongst natural fibres as it is strong, durable and unaffected by water. The main uses of hemp fibre were in rope, sacking, carpet, nets and webbing. A hemp clothing industry was reborn in the West in 1988, and hemp is being used in increasing quantities in paper manufacturing. The cellulose content is about 70%.
Harvesting the fibre
Smallholder plots are usually harvested by hand. The plants are cut at 2 to 3 cm above the soil and left on the ground to dry. Mechanical harvesting is now common, using specially adapted cutter-binders or simpler cutters.
The cut hemp is laid in swathes to dry for up to four days. This was traditionally followed by retting, either water retting whereby the bundled hemp floats in water or dew retting whereby the hemp remains on the ground and is affected by the moisture in dew moisture, and by moulds and bacterial action. Modern processes use steam and machinery to separate the fibre, a process known as thermo-mechanical pulping .
Fuel is often a by-product of hemp cultivation.
Millennia of selective breeding have resulted in varieties that look quite different. Also, breeding since circa 1930 has focussed quite specifically on producing strains which would perform very poorly as sources of drug material. Hemp grown for fibre is planted closely, resulting in tall, slender plants with long fibres. Ideally, according to Defra in 2004 the herb should be harvested before it flowers. This early cropping is because fibre quality declines if flowering is allowed and, incidentally, this cropping also pre-empts the herb's maturity as a potential source of drug material, even though the tetrahydrocannabinol (THC) content is very low.
The name Cannabis is the genus and was the name favoured by the 19th century medical practitioners who helped to introduce the herb's drug potential to modern English-speaking consciousness. Cannabis for non-drug purposes (especially ropes and textiles) was then already well known as hemp.
The name marijuana is Mexican (or Latin American) in origin and associated almost exclusively with the herb's drug potential. That marijuana is now well known in English as a name for drug material is due largely to the efforts of US drug prohibitionists during the 1920s and 1930s. We can surmise that this name was highlighted because it helped to characterise the herbal drug as quite alien to English-speaking culture.
There are broadly three groups of Cannabis varieties being cultivated today:
A nominal if not legal distinction is often made between hemp, with concentrations of the psychoactive chemical THC far too low to be useful as a drug, and Cannabis used for medical, recreational, or spiritual purposes.
From the 1881 Household Cyclopedia
The soils most suited to the culture of this plant are those of the deep, black, putrid vegetable kind, that are low, and rather inclined to moisture, and those of the deep mellow, loamy, or sandy descriptions. The quantity of produce is generally much greater on the former than on the latter; but it is said to be greatly inferior in quality. It may, however, be grown with success on lands of a less rich and fertile kind by proper care and attention in their culture and preparation.
In order to render the grounds proper for the reception of the crop, they should be reduced into a fine mellow state of mould, and be perfectly cleared from weeds, by repeated ploughings. When it succeeds grain crops, the work is mostly accomplished by three ploughings, and as many harrowings: the first being given immediately after the preceding crop is removed, the second early in the spring, and the last, or seed earth, just before the seed is to be put in. In the last ploughing, well rotted manure, in the proportion of fifteen or twenty, or good compost, in the quantity of twenty-five or thirty-three horse-cart loads, should be turned into the land; as without this it is seldom that good crops can be produced. The surface of the ground being left perfectly flat, and as free from furrows as possible; as by these means the moisture is more effectually retained, and the growth of the plants more fully promoted.
It is of much importance in the cultivation of hemp crops that the seed be new, and of a good quality, which may in some measure be known by its feeling heavy in the hand, and being of a bright shining color.
The proportion of seed that is most commonly employed, is from two to three bushels, according to the quality of the land; but, as the crops are greatly injured by the plants standing too closely together, two bushels, or two bushels and a half may be a more advantageous quantity.
As the hemp plant is extremely tender in its early growth, care should be taken not to put the seed into the ground at so early a period, as that it may be liable to be injured by the effects of frost; nor to protract the sowing to so late a season as that the quality of the produce may be effected. The best season, on the drier sorts of land in the southern districts, is as soon as possible after the frosts are over in April; and, on the same descriptions of soil, in the more northern ones, towards the close of the same month or early in the ensuing one.
The most general method of putting crops of this sort into the soil is the broadcast, the seed being dispersed over the surface of the land in as even a manner as possible, and afterwards covered in by means of a very light harrowing. In many cases, however, especially when the crops are to stand for seed, the drill method in rows, at small distances, might be had recourse to with advantage; as, in this way, the early growth of the plants would be more effectually promoted, and the land be kept in a more clean and perfect state of mould, which are circumstances of importance in such crops. In whatever method the seed is put in, care must constantly be taken to keep the birds from it for some time afterwards.
This sort of crop is frequently cultivated on the same piece of ground for a great number of years, without any other kind intervening; but, in such cases, manure must be applied with almost every crop, in pretty large proportions, to prevent the exhaustion that must otherwise take place. It may be sown after most sorts of grain crops, especially where the land possesses sufficient fertility, and is in a proper state of tillage.
As hemp, from its tall growth and thick foliage, soon covers the surface of the land, and prevents the rising of weeds, little attention is necessary after the seed has been put into the ground, especially where the broadcast method of sowing is practised; but, when put in by the drill machine, a hoeing or two may be had recourse to with advantage in the early growth of the crop.
In the culture of this plant, it is particularly necessary that the same piece of land grows both male and female, or what is sometimes denominated simple hemp. The latter kind contains the seed.
When the grain is ripe (which is known by its becoming of a whitish-yellow color, and a few of the leaves beginning to drop from the stems); this happens commonly about thirteen or fourteen weeks from the period of its being sown, according as the season may be dry or wet (the first sort being mostly ripe some weeks before the latter), the next operation is that of taking it from the ground; which is effected by pulling it up by the roots, in small parcels at a time, by the hand, taking care to shake off the mould well from them before the handsful are laid down. In some districts, the whole crop is pulled together, without any distinction being made between the different kinds of hemp; while, in others, it is the practice to separate and pull them at different times, according to their ripeness. The latter is obviously the better practice; as by pulling a large proportion of the crop before it is in a proper state of maturity, the quantity of produce must not only be considerably lessened, but its quality greatly injured by being rendered less durable.
After being thus pulled, it is tied up in small parcels, or what are sometimes termed baits.
Where crops of this kind are intended for seeding, they should be suffered to stand till the seed becomes in a perfect state of maturity, which is easily known by the appearance of it on inspection. The stems are then pulled and bound up, as in the other case, the bundles being set up in the same manner as grain, until the seed becomes so dry and firm as to shed freely. It is then either immediately threshed out upon large cloths for the purpose in the field, or taken home to have the operation afterwards performed.
The hemp, as soon as pulled, is tied up in small bundles, frequently at both ends.
It is then conveyed to pits, or ponds of stagnant water, about six or eight feet in depth, such as have a clayey soil being in general preferred, and deposited in beds, according to their size, and depth, the small bundles being laid both in a straight direction and crosswise of each other, so as to bind perfectly together; the whole, being loaded with timber, or other materials, so as to keep the beds of hemp just below the surface of the water.
It is not usual to water more than four or five times in the same pit, till it has been filled with water. Where the ponds are not sufficiently large to contain the whole of the produce at once, it is the practice to pull the hemp only as it can be admitted into them, it being thought disadvantageous to leave the hemp upon the ground after being pulled. It is left in these pits four, five, or six days, or even more, according to the warmth of the season and the judgment of the operator, on his examining whether the hempy material readily separates from the reed or stem; and then taken up and conveyed to a pasture field which is clean and even, the bundles being loosened and spread out thinly, stem by stem, turning it every second or third day, especially in damp weather, to prevent its being injured by worms or other insects. It should remain in this situation for two, three, four, or more weeks, according to circumstances, and be then collected together when in a perfectly dry state, tied up into large bundles, and placed in some secure building until an opportunity is afforded for breaking it, in order to separate the hemp. By this means the process of grassing is not only shortened, but the more expensive ones of breaking, scutching, and bleaching the yarn, rendered less violent and troublesome.
After the hemp has been removed from the field it is in a state to be broken and swingled, operations that are mostly performed by common laborers, by means of machinery for the purpose, the produce being tied up in stones. The refuse collected in the latter process is denominated sheaves, and is in some districts employed for the purposes of fuel. After having undergone these different operations, it is ready for the purposes of the manufacturer.
Hemp use dates back to the Stone Age, with hemp fibre imprints found in pottery shards in China over 10,000 years old.
Major hemp producing countries
From the 1950s to the 1980s the Soviet Union (now Russia) was the world's largest producer (3,000 km² in 1970). The main production areas were in Ukraine, the Kursk and Orel regions of Russia, and near the Polish border.
Other important producing countries were China, Hungary, the former Yugoslavia, Romania, Poland, France and Italy.
Canada, United Kingdom, and Germany all resumed commercial production in the 1990s. British production is mostly used as bedding for horses; other uses are under development. The largest outlet for German fibre is composite automotive panels. Companies in Canada, UK, USA and Germany among many others are processing hemp seed into a growing range of food products and cosmetics; many traditional growing countries still continue with textile grade fibre production.
Future of hemp
In the last decade hemp has been widely promoted as a crop for the future. This is stimulated by new technologies which make hemp suitable for industrial paper manufacturing, use as a renewable energy source (biofuel), and the use of hemp derivatives as replacement for petrochemical products.
The increased demand for health food has stimulated the trade in shelled hemp seed. Hemp oil is increasingly being used in the manufacturing of bodycare products.
Jesse Ventura was a vocal proponent of hemp cultivation while governor of Minnesota, though agricultural policymakers within his administration felt that hemp cultivation could not compete economically with crops such as corn and soybeans.
THC in hemp
Hemp contains delta-9-tetrahydrocannabinol (THC), which is the psychoactive ingredient found in hashish. THC is present in all hemp varieties to some extent. In varieties grown for use as a drug, where males are removed in order to prevent fertilization, THC levels can reach as high as 20-30% in the unfertilized females which are given ample room to flower.
In hemp varieties grown for seed or fibre use, the plants are grown very closely together and a very dense biomass product is obtained, rich in oil from the seeds and fibre from the stalks and low in THC content. EU regulations limit THC content to 0.3% in industrial hemp. In Canada, the THC limit is 1%.
On October 9, 2001, the US Drug Enforcement Agency (DEA) ruled that even traces of THC in products intended for food use would be illegal as of February 6, 2002. This Interpretive Rule would have ruled out the production or use of hempseed or hempseed oil in food use in the USA, but after the Hemp Industries Association (HIA) filed suit the rule was stayed by the Ninth Circuit Court of Appeals on March 7, 2002. On March 21, 2003, the DEA issued a nearly identical Final Rule which was also stayed by the Ninth Circuit Court of Appeals on April 16, 2003. On February 6, 2004 the Ninth Circuit Court of Appeals issued a unanimous decision in favor of the HIA in which Judge Betty Fletcher wrote, "[T]hey (DEA) cannot regulate naturally-occurring THC not contained within or derived from marijuana-i.e. non-psychoactive hemp is not included in Schedule I. The DEA has no authority to regulate drugs that are not scheduled, and it has not followed procedures required to schedule a substance. The DEA's definition of "THC" contravenes the unambiguously expressed intent of Congress in the Controlled Substances Act (CSA) and cannot be upheld". On September 28, 2004 the HIA claimed victory after DEA declined to appeal to the Supreme Court of the United States the ruling from the Ninth Circuit Court of Appeals protecting the sale of hemp-containing foods. Industrial hemp remains legal for import and sale in the U.S., but U.S. farmers still are not permitted to grow it.
Such stubbornness against a chemical widely thought to be less addictive or harmful than legal nicotine or alcohol leads some to suspect ulterior motives such as protection of the synthetic-fibre, wood pulp, petrochemical, and pharmochemical industries. (see conspiracy theory) The position has been an occasional embarrassment to the US government, as when they ignored their own arguments and grew it large-scale in Kentucky and Wisconsin for World War II.,
The presence of (some) THC in hemp varieties and the fear that THC could be extracted from industrial hemp for illegal purposes has hampered the development of hemp in many countries. Since the early 1990s, however, many countries, including Canada, Australia, the UK, The Netherlands and Germany, allow hemp plantings and commercial scale production. Plant breeders are working on the development of new varieties which are low in THC.