Hemp is an annual crop that can grow in a variety of climate conditions. Although it grows best when the surrounding temperatures are in the 60°F to 80°F range, hemp can handle conditions that are warmer or colder than optimum. In fact, hemp seedlings can even tolerate a little frost. Since hemp can be planted earlier than other crops, such as corn, it produces a sheltering canopy of leaves earlier, which means that weeds get shaded out sooner. This means farmers who raise industrial hemp don’t need herbicides to grow a healthy crop of hemp. The best quality hemp fiber comes from plants that receive at least four months of growing season before a killing frost. For hemp seed production, the growing season needs to extend to 5.5 months, to allow the seeds to fully mature before harvest.
Hemp plants require a good supply of moisture throughout the growing season, but especially during the early growth stage. Once the roots are developed, the plants can tolerate drier conditions, but the best quality hemp is raised in conditions with 20 to 28 inches of rain during the growing season. Drought conditions can force hemp plants to mature early, which means smaller plants.
The hemp plant can grow up to 20 feet tall. The stalk has a woody core, with a layer of bark that contains the long fibers which are found along the length of the stem. Growers have cross bred plants to make varieties of hemp that contain a high stem fiber content while at the same time having very low levels of THC.
To harvest hemp for fiber used in making ropes or fabric, the plants are cut after flowering, but before seeds mature. The next step is retting, which is related to “rotting." Hemp stalks are allowed to decompose a bit to the point where it is easy to remove the bark. The bacteria which break down the stalks require water and which can come from the air in field retting, or the stream or pool used for water retting. Field retting is more environmentally friendly, because when retting is done under water, the bacteria consume the oxygen which is needed by fish in the streams or ponds. In small amounts it is probably not a big issue but in large amount it could make river or lake water oxygen poor. Field retting requires careful monitoring by farmers to ensure that separation of the fibers occurs without too much deterioration from excess moisture. Weather conditions during retting and baling effect the quality of the fiber. Without retting, the fibers tend to break into shorter pieces that are unusable for woven cloth. After retting, the dried hemp stalks are ready for further processing.
Hemp photo by Zela.