Retting is the process of separating plant fibers by letting them lay on the ground to break down in the weather. This process is used on bast type plants like hemp. Bast type plants have a wood-like interior (the hurd) and a fibrous exterior (the bast). The bast exterior is extremely strong and has been used for things like sailcloth, clothing, and all manner of woven and non-woven goods. The hurd, with its woody inner core, is used for paper, insulation, hempcrete, and even has possibilities in 3D printing. The retting process separates these very useful parts of the plant.
The retting process is simple. Cut the plant and leave it laying in the field like mown grass. Turn it every few days for 14 to 28 days to degrade certain materials that bind the bast and hurd. This process can utilize the dew content, or it can be watered depending on the conditions.
According to an article published in 2011, “Hemp (Cannabis sativa L.) is the earliest developed source of plant bast fibre” (Tahir). So this process has been around as long as humans have used plant fibers to weave. Properly retted hemp will yield stronger, higher quality fiber that can be used in many applications. Once the retting process is properly completed, farmers can bail the material just like hay and it is well on its way to becoming a useful industrial hemp product.
Tahir, Paridah. Ahmed, Amel. SaifulAzry, Syeed. Ahmed, Zakiah. (2011). Retting process of some bast plant fibres and its effect on fibre quality: A review. BioResources. 6. 5260-5281.