Flax, known scientifically as Linum usitatissimum, is a plant cultivated for two main purposes: producing seed for oil and growing long, strong fiber for textiles. This guide focuses specifically on cultivating the plant for its fiber, which is processed into linen. Growing flax for fiber requires a distinct approach compared to growing it for seed, primarily by managing plant density to encourage tall, unbranched stems suitable for high-quality linen. The success of the final fiber is determined by precise cultivation methods, from preparing the soil to the complex, post-harvest biological process of retting.
Site Preparation and Planting Requirements
Selecting the right location for fiber flax requires an open site that receives full sun exposure. The ideal soil is a deep, fertile, well-drained sandy clay loam, with a slightly acidic to neutral pH range, optimally between 5.5 and 7.0. It is best to prepare the seedbed finely, often in the previous autumn, to ensure the soil is loose and free of rocks and debris for optimal seed germination and root development.
Planting must occur as early in the spring as the soil can be worked, typically when the soil temperature reaches about 6–8°C (43–46°F). Early sowing is preferred because it generally results in better yields and fiber quality. The shallow planting depth of approximately 1.5 to 2 centimeters is necessary to ensure quick emergence.
Fiber flax is sown at a very high density, aiming for a stand of about 175 to 200 plants per square foot. This close spacing forces the plants to compete for light, which inhibits branching and results in tall, slender, straight stems that maximize the length of the usable fiber.
Nutrient management is important, as excessive nitrogen application can reduce fiber quality and increase the risk of lodging. Nitrogen is required at lower rates than for other crops, with an emphasis placed on phosphorus for root development and potash (potassium) to support strong fiber growth. A firm seedbed is essential after planting, often achieved by lightly rolling the area to ensure good seed-to-soil contact, which aids uniform germination.
Managing Growth
Once the flax has germinated, the main challenge is managing competition, as flax is a poor competitor against weeds, especially in its early stages. Weed control is necessary during the first few weeks of growth, before the flax plants are tall enough to shade out other plants. Weeds reduce the fiber quality and length by competing for moisture and nutrients.
Weeding should ideally be completed before the flax reaches about 15 centimeters in height. The dense planting for fiber makes mechanical or chemical control difficult, so pre-emergent strategies are often used to start with a clean field. Flax is drought-tolerant once established, but it does require adequate moisture during the early growth phase and through flowering.
Irrigation can be helpful during a drought, but it should be reduced or stopped once the seed heads begin to form, preventing the stalks from becoming overly lush and prone to lodging. Monitoring for common pests and diseases, such as Pasmo, allows for timely intervention to protect the developing stems. The goal throughout this period is to maintain the integrity of the tall, thin, unbranched stalk that holds the long bast fibers.
Determining the Optimal Harvest Time
Harvest timing directly influences the quality and fineness of the finished linen fiber. Harvesting too early yields fine fiber but immature seeds, while waiting too long produces coarse, brittle fiber. The optimal window for harvest is often narrow, occurring approximately 90 to 100 days after planting, or about 30 days after the plant finishes flowering.
Visual cues are used to pinpoint this moment: the lower third of the flax stalk should be turning yellow, while the upper portion is still green. The seed bolls will have turned from green to a pale brown or yellow color, indicating that the seeds inside are formed but not yet fully ripe. Harvesting at this stage balances fiber strength and fineness with the ability to collect viable seeds.
For maximum fiber length, the preferred method is to pull the entire plant, roots and all, out of the ground. Pulling ensures that the full length of the fiber, which extends into the root crown, is preserved. After pulling, the stalks are immediately bound into bundles, or sheaves, and stood upright in the field to dry completely, preparing the straw for the next processing stage.
The Critical Step of Retting
The first step in post-harvest processing is retting, a controlled biological decomposition that releases the bast fibers from the plant’s woody core, known as the shive or boon. This process uses moisture and microorganisms to break down the pectin, a glue-like carbohydrate substance that binds the long fibers to the stem. Retting is essential because without it, the fibers cannot be separated without damage.
The two main traditional methods are dew retting and water retting. Dew retting involves spreading the dried flax stalks thinly and evenly on a grassy field. Natural dew, rain, and airborne fungi and bacteria work over several weeks to dissolve the pectin. This method is dependent on consistent weather conditions and yields a naturally darker, more variable fiber color.
Water retting is a faster, more controlled method where bundles of flax straw are submerged in tanks or bodies of water for a period ranging from a few days to two weeks. Bacteria in the water perform the anaerobic decomposition, which produces a more consistent, lighter-colored fiber, but it requires careful management of water temperature and time.
Regardless of the method, the process must be carefully monitored to avoid under-retting, which makes fiber separation difficult, or over-retting, which weakens the fibers themselves. Experienced growers use a “break test” to determine when retting is complete, which involves drying a small sample of straw and physically breaking it. When properly retted, the woody inner shive should snap easily and separate cleanly from the long, intact outer fiber bundles. This finished material is then dried again before the next mechanical steps of fiber extraction.