Woad and Indigo

A bucket of pale, crystal-green water. A skein of yarn. Combine and discover the magic blues of woad and indigo.

Photo by Adobe Stock/goodmanphoto

Blue is among the most coveted of natural dye colors, in large part because true blue pigments are rare in nature. Many blue flowers are actually purple-tinged, and while animals, such as birds, fish, and lizards, often make use of refractive scales and feathers to appear blue, that’s caused by a trick of the light rather than imbedded pigments. Of the plants that do produce blue pigments, indigo and woad are by far the most well-known, and both are rich sources of indigotin, a crystalline compound that’s the main constituent of indigo dye. This article is the second of a two-part series on natural dye plants that create primary colors; we discussed plants that produce red and yellow dyes in “Madder and Weld,” Heirloom Gardener, Winter 2019.

Growing Woad

Woad (Isatis tinctoria) is a cruciferous plant — a member of the cabbage family, like broccoli and mustard — native to Turkey and the Mediterranean, though it’s now naturalized throughout Europe and much of North America. It may be most famous for its use in the skin paint Celtic warriors applied before battle. In addition to its striking blue color, it has mild antiseptic properties. Woad will readily spread in rich, high-nitrogen soils, but it can tolerate poor soils provided it’s in full sun and well-watered. The biennial plants make low clumps of oval leaves in their first year, and send up tall flowering stalks with masses of bright-yellow blooms the following spring.

Most dyers use first-year leaves for color, and allow only a few plants to bloom and set seed; each flowering stalk will produce huge quantities of seeds for saving. Because of their tendency to reseed, woad is considered invasive in the western United States, so check with your local extension office before you make plans to grow it. Direct-sow the seeds about 1⁄2  inch deep in spring, and water them well. The seed coats have a germination inhibitor that must be washed away before they’ll sprout. Reports vary on how far to space plants; denser planting means less weeding, but more competition for water and nutrients, so weigh your options.

Harvesting Woad

The indigotin content in woad leaves depends on the soil’s nitrogen content and the plant’s access to heat and sunlight. Harvesting after a hot, sunny period will yield far more blue dye than harvesting in cloudy weather.

Photo by Adobe Stock/Erik



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