Indigo, a member of the pea family native to India, is a tropical deciduous shrub that bears small reddish pink flowers. Although the leaflets and branches of many Indigofera species yield a natural blue dye, I. tinctoria — which was used at least 6,000 years ago in China — is used most commonly today. Approximately 660 pounds of I. tinctoria are required to produce about 2.2 pounds of dye. The ancient Greek word for the dye, indicon, means “blue dye from India.” Ancient Romans used the word indicum, which later became “indigo” in English. The worldwide cultivation of indigo declined sharply with the advent of synthetic dyes in the 20th century.
Common Names: Indigo, True Indigo
Description: Deciduous shrub, 2 to 6 feet tall; small reddish flowers produced in racemes; opposite leaflets
Hardiness: To Zone 9
Flowering: June and July
Parts Used: Leaves, stem, and roots
Range/Habitat: Native to India, naturalized in Hawaii and the southern United States
Although not often used in contemporary Western herbal medicine, indigo root and stem are thought to cleanse the liver and blood, relieve pain, reduce inflammation, and fight fever. In one animal study with rats, indigo was shown to have liver-protectant properties. In Ayurvedic medicine, indigo has a broad range of uses: It promotes hair growth, acts as a purgative, treats intestinal obstructions, and can be used in a poultice to treat skin conditions such as scabies, wounds, and sores. Fresh leaf juice is used to treat whooping cough, asthma, and heart palpitations. The herb known as wild indigo (Baptisia tinctoria), also of the pea family, is used medicinally as an astringent, anti-inflammatory, antiseptic, and fever reducer, but it contains several compounds that are quite toxic.
The fermented leaves of this species can be used to produce a blue dye for fabric. To ferment the leaves, steep them in water for 12 to 48 hours, stirring frequently. The blue sediment that forms is the dye.
How to grow it
This frost-tender tropical plant prefers a hot, humid climate, full sun, and well-drained sandy loam. It will not thrive in clay. In colder regions, grow it as an annual. To improve germination, scarify the seeds gently with sandpaper, then soak them in warm water for 24 hours before sowing. Prune hard to encourage the new growth that produces flowers. Propagate by cuttings taken in summer. A nitrogen fixer, indigo enriches the soil where it is grown.