Flax seeds - Linum usitatissimum - green manure

Cultivated Flax, Linum usitatissimum in Latin, is an annual plant that can be used as green manure. Through its powerful root system, it loosens the soil, improves soil structure, limits the proliferation of weeds, and helps prevent soil leaching or compaction caused by rain. Sown in spring in March-April, this flax produces lots of typical, delicate blue flowers in the summer, creating a beautiful effect. It is effective in clayey soil thanks to its multiple rootlets that break up the soil.

Cultivated flax is native to temperate and subtropical regions of the northern hemisphere and belongs to the linaceae family. It is an annual plant that forms a cluster of slender stems covered with green-blue foliage, composed of very fine, 1 to 3 cm (0 to 1in) long, lanceolate leaves. When in bloom, flax forms bushy clumps that can reach up to 1m (3ft) high. Flowering occurs, depending on the region, in the form of corymbs of five-petaled, light blue flowers with a flared funnel shape from June to August. They form terminal panicles and are borne on an upright and elongated peduncle. They wither during the day. This plant readily self-seeds in light soil. Cultivated flax has carbon-rich stems that provide humus.

Green manures like cultivated flax have many benefits and are widely used in organic gardens. They nourish and improve the soil by providing it with various nutrients and stimulating the soil's microbial life. Their roots loosen, break up, and aerate the soil. The vegetative cover protects the soil from leaching (nutrient loss in sandy soil), rain compaction (crusting in loamy soil), and erosion (due to runoff on sloping terrain during heavy rainfall). This vegetative cover also helps suppress weed growth by preventing the growth of weeds. Finally, green manures are often nectar-rich and attract pollinators.

Green manures can be sown on uncultivated plots or between rows of vegetables. They are either naturally destroyed by frost or cut before seed formation. Once cut down, they can be left in place as mulch, or crushed and incorporated into the top layers of the soil, or collected and added to compost.