Common Name: Indigo

General Information

Indigofera tinctoria is an erect, copiously-branched perennial plant growing 1 - 2 metres tall. The spreading or ascending branches become more or less woody and can persist for more than a year[].
Indigo, of which this species is a major source, has a very long history of use as a dye. Because of its fascinating deep blue colour, its great colour fastness to light and the wide range of colours obtained by combining it with other natural dyes, it has been called 'the king of dyes' and no other dye plants have had such a prominent place in as many civilizations as this genus. It was at one time widely cultivated for this purpose but, with the advent of synthetic dyes, demand for the plant has dropped dramatically[]. This species has been used by humans for over 4,000 years, with examples of its use being found in the cloth of ancient Egyptian mummies[]. The plant also has a range of other traditional uses, particularly in traditional medicine.

Known Hazards

None known

Botanical References

,

Range

Probably originally from Malaysia, the plant now has a pantropical distribution.

Habitat

Not known

Properties

Weed Potential	Yes
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Deciduous Shrub
Height	2.00 m
Cultivation Status	Cultivated

Cultivation Details

Indigofera tinctoria is a plant of the tropics and subtropics, where it is found at elevations up to 1,600 metres. It grows best in areas where annual daytime temperatures are within the range 22 - 28°c, but can tolerate 7 - 32°c[]. It prefers a mean annual rainfall in the range 1,300 - 1,700mm, but tolerates 640 - 3,000mm[].
Requires a position in full sun, succeeding in any deep, well-drained and moderately retentive and fertile soil[]. Prefers a pH in the range 6 - 7, tolerating 4.3 - 8.7[]. Requires a position sheltered from hot winds[].
Indigofera tinctoria has been widely spread through the tropics and subtropics as a result of cultivation as a dye plant. It has the potential to invade native ecosystems and poses both a present and a future threat. The species was included in Kaufman's 2013 'Invasive Plants of North America'[].
Branches are harvested by cutting 10 - 20cm above ground level when the plants are 4 - 5 months old and have formed a closed stand, usually at the flowering stage[]. The crop should be harvested promptly because heavy rains or flooding can destroy it in a few hours. In India harvested branches are tied into bundles of about 130 kg and transported to the dye factory. Up to 3 harvests are possible per year[].
Dye yields can be 1.6 - 5.4 tonnes per hectare[].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[].

Edible Uses

The deep blue dye obtained from the leaves is sometimes used to counteract the slightly yellow colour of icing sugar[].

Medicinal

A leaf infusion (sometimes combined with honey or milk) is used to treat a range of disorders including epilepsy and nervous disorders; asthma and bronchitis; fever; complaints of the stomach, liver, kidney and spleen; and as a rabies prophylactic[].
Applied externally, the leaves are made into an ointment for treating skin diseases, wounds, sores, ulcers and haemorrhoids[].

A tincture of the seed is used in India to kill lice[].

A root preparation is applied to relieve toothache, syphilis, gonorrhoea and kidney stones[].
A watery root paste is applied topically in India to treat worm-infested wounds[]. A root infusion is used there as an antidote against snakebites and to treat insect and scorpion stings[].

An aqueous acetone extract of the leaves and stems is rich in polyphenols and flavonoids and has been shown to be an effective antioxidant[].

Agroforestry Uses:

The plant is sometimes grown as a cover crop and green manure[].
Indigofera tinctoria is useful as a green manure, it is used in India, for example, in coffee plantations and as a cover crop preceding rice, maize, cotton and sugarcane[].
In traditional rainfed rice cropping systems in the Philippines, this plant is a popular green manure, increasing rice yield whilst also reducing by 50% the need to supply expensive nitrogen fertilizer[].
The residue remaining after indigo extraction is also applied to the land as manure[].
Another reason to grow Indigofera tinctoria as a green manure is because it is a good nitrogen catch crop, reducing the amount of fertilizer NO3 leaching to the groundwater[].

Other Uses

A deep blue dye is obtained from the leaves[, , ]. The leaves and twigs do not actually contain indigo but colourless precursors that must be extracted and then processed in order to produce the indigo dye[].
The harvested leafy branches are placed in a tank containing water to which some lime has been added, and are weighted down with planks[]. After some hours of fermentation, during which enzymic hydrolysis leads to the formation of indoxyl, the liquid is drained off and then stirred continuously for several hours to stimulate oxidation of the indoxyl[]. Afterwards the solution is left to rest and the insoluble indigo settles to the bottom as a bluish sludge[]. The water is drained and after the indigo has dried, it is cut into cubes or made into balls[].
To dye textiles, indigo is reduced to a soluble form by a fermentation process under alkaline conditions. In traditional preparations of the dye, various reducing agents such as molasses are used, together with coconut-milk, bananas and the leaves of Psidium guajava[]. The alkalinity is maintained by adding lime. After the textile has been dipped into solution it turns blue when exposed to the air[].

The twigs are used as toothbrushes[].

The dried, crushed leaves are used as an ingredient in commercial cosmetic preparations as a masking agent and tonic[].
An extract of the leaves is used as an ingredient in commercial cosmetic preparations as a skin conditioner[].

Propagation

Seed - pre-soak overnight in warm water and sow in a seedbed with partial shade. Germination takes about 4 days[].
Like many species within the family Fabaceae, once they have been dried for storage the seeds of this species may benefit from scarification before sowing in order to speed up and improve germination. This can usually be done by pouring a small amount of nearly boiling water on the seeds (being careful not to cook them!) and then soaking them for 12 - 24 hours in warm water. By this time they should have imbibed moisture and swollen - if they have not, then carefully make a nick in the seedcoat (being careful not to damage the embryo) and soak for a further 12 hours before sowing[].
Semi-ripe cuttings of lateral shoots with a heel[].
Root cuttings.

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