Hemp, Cannabis sativa L, is an industrial crop and is one of the oldest cultivated crops in the world. Hemp is cultivated in many countries, including, China, Canada, Russia, the USA, and several European countries. In these countries hemp farming is regulated.
It is illegal to cultivate hemp in South Africa as it is classified under the Cannabis species. A permit is required before one can plant hemp and this permit is obtained from the Department of Health under the Medicines Control Council.
The plant has been used for a wide variety of purposes. It is used to make over 25,000 consumer products, from hemp apparel and accessories to house-wares and hempseed oil cosmetics. Some of the products made from hemp are: clothing, shoes, diapers, rope, canvas, cellophane, paints, fuels, chain lubricants, biodegradable plastics, paper, fibreboard, cement blocks, food, cosmetics, and soap.
Hemp is described as an annual herbaceous plant with an upright growth habit and its characteristic leaves are composed of five to seven leaflets. The hemp plant can reach nine metres in height, but under cultivation it averages between two to four metres. Hemp is from the same plant species (Cannabis) as dagga (marijuana). Although similar in appearance, the dagga plant may develop more side branches and has a more bushy appearance in contrast with hemp. Hemp is mainly cultivated for fibre and oil and because the delta-9-tetrahydrocannabinol (THC) content is very low, it cannot be used as a drug. Dagga, on the hand, has such a low fibre content that it is not suitable for fibre production. Hemp generally refers to the fibre-producing strain of Cannabis. Currently three main groups of varieties under cultivation, namely, varieties cultivated primarily for fibre, varieties grown for seed and varieties grown for their medicinal and narcotic properties.
The hemp plant makes heavy demands on the soil. The hemp taproot can penetrate deep into the soil but lateral roots are primarily responsible for the uptake of nutrients, water and oxygen. The hemp plant needs a sufficiently deep, well aerated soil, as well as regular water supply. It grows best on highly fertile soils which contain abundant organic matter, i.e., neutral or slightly alkaline, well-drained loam soil with good water holding capacity.
The hemp plant requires a mild, temperate climate and an annual rainfall
or irrigation of at least 500 to 700 mm. For optimum yield, it requires 250 to
300 mm of moisture during the vegetative growing stage. Droughts are damaging,
especially while the seed is germinating and during flowering. Hemp grows best
when supplied with moisture throughout its growing season and especially in its
early stages of growth or during the first six weeks of growth. The hemp plant
is sensitive to short day length which induces early flowering. It requires a
day length of between 14 and 16 hours. A short day length also inhibits stem
growth and decreases the production of fibre hemp after flowering. Currently
suitable growing areas in South Africa are limited to the Western and Eastern
Cape regions during the summer where there is a maximum of 13 to 14.4 hours of
daylight.
Row spacing and seeding rate are important factors in hemp production
because they influence the growth, biomass production and fibre yield of the
hemp plant. Low seeding rate and wide inter-row spacing produce large, branched
plants that seed heavily. The growth of widely spaced hemp plants is
impressive, but the bast fibre production of such plants is relatively low and
fibre separation is difficult due to the presence of branches. High seeding
densities in any crop result in self-thinning due to the interplant competition
for water, nutrients and light.
The planting date is another important factor in fibre hemp production. As hemp is sensitive to day-length, the vegetative growth period should be maximized. Therefore, an early planting date (October to November in the Eastern and Western Cape) results in taller plants with higher fibre yields, while later planting will result in early flowering and poor fibre production. Hemp is ready for harvest 120 days after planting.
The method used for harvesting hemp is determined by the use to which the hemp will be put. The common method of harvesting hemp for seed is to cut it by hand but it can also be harvested mechanically. If hemp is harvested for fibre, early harvesting will result in low fibre yield and late harvesting in coarse fibre.
