Dyer’s woad (Isatis tinctoria), a member of the mustard family, is native to the Mediterranean and Western Asia and quickly moved into Europe. The “dyer’s” portion of the common name refers to the indigo blue dye derived through a complex process involving repeated fermentations of the plant. As far back as the neolithic (10,000 to 5,000 BC) dyer’s woad seeds were collected and stored. The Egyptians used dyer’s woad to dye linen by 2,500 BC; Dioscorides, a Greek physician, refers to woad as a dye source in the First Century AD; ancient Britons dyed their bodies blue with woad; and during the Middle Ages large tracts of woad were cultivated for use in preparing blue dye. In Colonial times dyer’s woad was introduced to the Western Hemisphere. “Woad” is an Old English word for the blue dye.
Dyer’s woad is often cultivated by practitioners of the traditional art of dyeing with natural plants. Once dyer’s woad escapes cultivation it is first found along roadsides and other disturbed sites from which the plant spreads to range lands and croplands via seeds and can form dense stands. Dyer’s woad has a thick tap root that may exceed five feet in depth. The plant will regenerate from the root if the top is mechanically removed. Because it aggressively competes with agricultural and native plants, dyer’s woad is considered a noxious weed.
A biennial (or sometimes a short-lived perennial), dyer’s woad forms a basal rosette of leaves the first winter. The following summer a single, tall stem topped by a broad, rounded inflorescence can grow up to four feet in height. The alternate stem leaves are arrow shaped, blue green in color and have a whitish nerve (vein) on the upper surface. The bright yellow flowers of dyer’s woad have four petals in a Maltese Cross formation. In the photograph the flower appears to have eight petals, but four of the “petals” are sepals. These yellow sepals are visible protecting the unopened buds. Numerous flat brown or purple-black, sausage-shaped seedpods all hang downward and contain a single seed. The greenish immature seedpods can be seen in the pictures.
In midsummer herbalists pick and dry dyer’s woad leaves for use as an astringent (draws together and contracts organic tissues) or styptic. The leaves are used directly as a poultice to soothe boils, bring them to a head and discourage the boils from infecting. Wounds and bruises are treated by dropping dyer’s woad leaves in water for a few seconds, cooling them and placing the treated leaves on the affected area. I have never tried using dyer’s woad as a dye or medicinally.
These photographs were taken along County Road 87 near Adin CA (Modoc County) where dyer’s woad has infested abandoned farmland. These fields are a beautiful riot of yellow because of the woad, however nearby land under cultivation or used for grazing is threatened.