Hemp (Cannabis sativa), an agricultural crop native to Central Asia, is now widespread throughout tropical and temperate climates. It adapts to the local climate and soil type and is ‘reported to tolerate disease, drought, fungus, high pH, insects, laterite, low pH, mycobacterium, poor soil, slope and weeds’(1). Although the plant does readily adapt to most soil types, it ‘thrives in rich, fertile, neutral to slightly alkaline, well-drained silt or clay loams with moisture retentive subsoil’(2). It is a fast growing, hardy plant, in the UK producing an annual harvest with stalks reaching up to 4m high.
Hemp is grown for many uses, but is most widely cultivated for the bast (phloem) fibre in the stem. The stem has ‘two constituent parts: a fibre sheath around a woody core called shiv(3), shive or hurd’(4). The fibre is highly valued due to its length, strength and durability with a particular resistance to decay and has been heavily used for ropes, nets, sails and paper. As Small and Marcus note, hemp is one of the ‘oldest sources of textile fibre, with extant remains of hempen cloth trailing back 6 millennia’. (5)
In contrast to the high quality fibre, the shiv is the least valuable part of the plant. It does have some short fibres but is principally cellulose, ‘chemically very close to wood’(6). With low tensile strength it is seen as a bi-product. The mechanical separation of the fibre from the shiv results in the shiv being broken into small pieces which until 1985 were predominantly used as animal bedding and mulch. It is this waste product that is now used within lime-hemp as a construction material.