Coarse, bushy herb up to 4m tall. Leaves grey-green, up to 12cm long, palmate with 3-9 lanceolate leaflets, margin serrated. Individual plants either have male or female flowers (dioecious). Flowers small, green and clustered. Fruits small, dry and thin-walled (achene), contain only one seed. Pollinated by wind.
The hemp at Eden is grown under an industrial licence.
Hemp plants can grow up to 4m tall.
Hemp growing at Eden
Nathan tells us why hemp is such an important crop.
- Hemp grows fast, is very adaptable to soil and climatic conditions and is undemanding on resources such as artificial fertilisers and pesticides. It provides a good break crop for the farmer, giving the land a rest from other crops and helping to prevent disease.
- It is a potential flagship sustainable crop for the 21st century, but there’s a reason why our fields aren’t full of it. It produces a substance that became socially controversial in the early part of the 20th century: tetrahydrocannabinol (THC), which as well as having many medicinal attributes has been used as a recreational drug. In recent years breeding and selection has resulted in cultivars low in THC, and hemp is once again being considered by governments as a useful crop.
- One of the oldest relics of human industry is a bit of hemp fabric dating back to approximately 8,000 BC.
- Hemp is six times as strong as cotton, much more resistant to weathering and wear, and more lustrous and absorbent. It is also much more environmentally friendly to grow.
- Hemp growing became commonplace in Britain under the Romans and continued into the mid-1940s. In the 16th century Henry VIII made hemp cultivation obligatory. He was interested in it for making rope – very important, especially to ships in those days.
Where it grows
Originally from the Indian subcontinent, it spread from China to France and from Russia to Africa. It requires full light but can grow in most soil types providing they are damp.
For centuries hemp has provided raw materials for paper, textiles, rope for ships, medicine, oil and much more. It is one of the most useful multi-purpose crops of the temperate world quoted as having over 25,000 end products. For example, the seed can be used as a food protein and the outer stem provides fibre for ropes and canvas for tents. It is illegal in most countries because the leaves of the high-THC types can be dried and smoked to provide a mild narcotic.
The fibre crop grown in Europe has no THC and mostly supplies the specialist paper industry and the non-woven converting industry, which supplies automotive companies.
In order to grow hemp at Eden we needed an industrial licence and a physical barrier, so the barrier became the artistic installation: the Hemp Fence designed by George Fairhurst. It is also a symbolic barrier: visitors are invited to stick their neck out to see what is on the other side.
Read fascinating facts and browse beautiful, detailed photos of hemp (Cannabis sativa): one of thousands of plant species growing at the Eden Project in Cornwall.
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Hemp, (Cannabis sativa), also called industrial hemp, plant of the family Cannabaceae cultivated for its fibre (bast fibre) or its edible seeds. Hemp is sometimes confused with the cannabis plants that serve as sources of the drug marijuana and the drug preparation hashish. Although all three products—hemp, marijuana, and hashish—contain tetrahydrocannabinol (THC), a compound that produces psychoactive effects in humans, the variety of cannabis cultivated for hemp has only small amounts of THC relative to that grown for the production of marijuana or hashish.
The hemp plant is a stout, aromatic, erect annual herb. The slender canelike stalks are hollow except at the tip and base. The leaves are compound with palmate shape, and the flowers are small and greenish yellow. Seed-producing flowers form elongate, spikelike clusters growing on the pistillate, or female, plants. Pollen-producing flowers form many-branched clusters on staminate, or male, plants.
Cultivation and processing
Hemp originated in Central Asia. Hemp cultivation for fibre was recorded in China as early as 2800 bce and was practiced in the Mediterranean countries of Europe early in the Christian era, spreading throughout the rest of Europe during the Middle Ages. It was planted in Chile in the 1500s and a century later in North America.
Hemp is grown in temperate zones as an annual cultivated from seed and can reach a height of up to 5 metres (16 feet). Crops grow best in sandy loam with good drainage and require average monthly rainfall of at least 65 mm (2.5 inches) throughout the growing season. Crops cultivated for fibre are densely sowed and produce plants averaging 2–3 metres (6–10 feet) tall with almost no branching. Plants grown for oilseed are planted farther apart and are shorter and many-branched. In fibre production, maximum yield and quality are obtained by harvesting soon after the plants reach maturity, indicated by the full blossoms and freely shedding pollen of the male plants. Although sometimes pulled up by hand, plants are more often cut off about 2.5 cm (1 inch) above the ground.
Fibres are obtained by subjecting the stalks to a series of operations—including retting, drying, and crushing—and a shaking process that completes separation from the woody portion, releasing the long, fairly straight fibre, or line. The fibre strands, usually over 1.8 metres (5.8 feet) long, are made of individual cylindrical cells with an irregular surface.
Products and uses
The fibre, longer and less flexible than flax, is usually yellowish, greenish, or a dark brown or gray and, because it is not easily bleached to sufficiently light shades, is rarely dyed. It is strong and durable and is used for cordage—e.g., twine, yarn, rope, cable, and string—and for artificial sponges and such coarse fabrics as sacking (burlap) and canvas. In Italy some hemp receives special processing, producing whitish colour and attractive lustre, and is used to make fabric similar to linen. Hemp fibre is also used to make bioplastics that can be recyclable and biodegradable, depending on the formulation.
The edible seeds contain about 30 percent oil and are a source of protein, fibre, and magnesium. Shelled hemp seeds, sometimes called hemp hearts, are sold as a health food and may be eaten raw; they are commonly sprinkled on salads or blended with fruit smoothies. Hemp seed milk is used as an alternative to dairy milk in drinks and recipes. The oil obtained from hemp seed can be used to make paints, varnishes, soaps, and edible oil with a low smoke point. Historically, the seed’s chief commercial use has been for caged-bird feed.
Although only the hemp plant yields true hemp, a number of other plant fibres are called “hemp.” These include Indian hemp (Apocynum cannabinum), Mauritius hemp (Furcraea foetida), and sunn hemp (Crotalaria juncea).
The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Melissa Petruzzello, Assistant Editor.
Hemp, cannabis plant cultivated for its useful bast fiber and nutritious edible seeds. The variety of cannabis cultivated for hemp fiber and hemp seeds has only small amounts of psychoactive THC relative to cannabis grown for the production of marijuana or hashish.