Isatis tinctoria. Also known as Dyer’s Woad. It is a tall biennial which has shiny blue-green leaves and bears clusters of delicate yellow flowers. The leaves of this plant are the source of a blue dye, often used instead of indigo. The leaves are crushed into a pulp, molded into balls, dried in the sun and allowed to ferment before being pulped again and formed into cakes to produce blue dye. As well as being used for clothing, woad was once used by Celtic warriors to stain their bodies during battle.
Grow in a sunny position. It will reach a height of 100cm.