Fibre Production

A cross section of a hemp stem shows a green "bark" containing very long, strong fibres. These are the bast fibres that have been used for centuries to make clothing, rope, twine, and paper etc.. The white core, called "hurd", is very light and corky, but contains some very short fibres useful in livestock bedding, pulping or in building materials.

A process called retting helps the separation of the bast and hurd fibres by breaking down the bond that holds the fibres together. Traditionally, retting is accomplished by letting the stalks lay in the field for several weeks depending on weather conditions (dew retting) prior to baling. Research is needed to determine if these swaths will need to be turned at some point to assist retting. After retting, the stalks are mechanically decorticated (the long fibres are separated from the hurds). Without retting, decortication can result in fibre with relatively high hurd content, or increase the cost of decortication.

Hemp as a fibre only crop, is cut when the male plants are in full flower and shedding pollen before viable seed set. Mower/conditioners and round-balers have been found suitable with limited modification. The hemp fibre will routinely be cut in mid August, and lay in the field to “dew” rett for 4 to 6 weeks depending on the weather. After the bast and hurd separate easily it will be ready to bale. Retting separates the bast and the hurd but also helps separate the fibre bundles. Without retting, processing will be more difficult. Limited research indicates that fibre yields can be increased by higher seeding rates that result in higher plant populations.

Dual purpose (grain and fibre harvest)

After combining, the remaining stalk material can be cut and baled and utilized in the fibre market. Retting of these stalks is also very important. The stalks may have to rett in the field for several weeks after combining. This may cause a problem in a year when there is a late harvest. A typical fibre harvest after combining may need to be done in the spring to facilitate retting.

Alternatives to field retting include enzymatic retting, ultrasonic retting, and retting by ensiling, but these approaches are new and need research. Fibre quality requirements will have to be developed as processors begin to find out qualities that enhance their end product.