This famous plant makes a dividing clump of shiny leaves, above which arise masses of small yellow flowers which in turn produce sprays of unusual elongated seeds. This is the plant made famous as the source of the most important blue natural dye, used by the Celts, the ancient people of the British Isles (& Braveheart!). The leaves must be dried and then steeped and fermented in water to produce a deep blue dye that is useful for ruining your clothes, or maybe painting your face blue to frighten visitors............
For best results, sow immediately onto a good soil-based compost. Cover the seeds with fine grit or compost to approximately their own depth. They can be sown at any time, and germination can sometimes be quicker if kept at 15 to 20 degrees C. We sow most seeds in an unheated greenhouse and wait for natural germination, as many seeds have built-in dormancy mechanisms, often waiting for natural spring germination, hence giving them a full season of growth.