By: Liz Baessler
Indigofera tinctoria, often called true indigo or simply just indigo, is probably the most famous and widespread dye plant in the world. In cultivation for millennia, it has fallen somewhat out of favor recently due to the invention of synthetic dyes. It’s still a wonderfully useful plant, however, and very much worth growing for the adventurous gardener and home dyer. Keep reading to learn more about growing indigo plants in your garden.
What is True Indigo?
Indigofera is agenus of over 750 species of plants, many of which go by the common name“indigo.” It’s Indigofera tinctoria,however, that gives indigo color, so named for the deep blue dye it produces,which has been used for thousands of years.
The plant is thought to be native to Asia or northernAfrica, but it’s difficult to be sure, since it’s been in cultivation since atleast 4,000 BCE, long before good gardening records were being kept. It hassince been naturalized the world over, including the American South, where itwas a very popular crop in Colonial times.
These days, tinctoria indigo isn’t grown nearly as extensively, as it has been overtaken by synthetic dyes. As with other indigo varieties, however, it’s still an interesting addition to the home garden.
How to Grow Indigo Plants
Indigo plant care is relatively simple. Tinctoria indigo ishardy in USDA zones 10 and 11, where it grows as an evergreen. It prefersfertile, well-drained soil, moderate moisture, and full sun, except in very hotclimates, where it appreciates some afternoon shade.
A medium shrub, the indigo plant will grow to 2-3 feet (61-91.5 cm.) in height and spread. In the summer, it produces attractive pink or purple flowers. It is actually the plant’s leaves that are used to make the blue dye, though they are naturally green and must go through an involved extraction process first.
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How to Grow Indigofera Tinctoria
One of the oldest plants in cultivation, Indigofera Tinctoria, or true indigo, has been cultivated and used for thousands of years as a natural dye. Indigo dye appears as a dark blue or violet-blue pigment, and was widely used for dyeing clothing, including blue jeans, before the advent of artificial indigo dye. Although used by relatively few garment and textile manufacturers today, natural indigo is still grown on farms that provide the dye to manufacturers of premium denim, as well as by amateur gardeners and natural dye enthusiasts. An herbaceous perennial, Indigofera Tinctoria is best suited to U.S. Department of Agriculture plant hardiness zones 9 and above, but it also can be grown as an annual in colder climates.
Choose a site that receives a few hours of direct sunlight each day, preferably with a south or southeast exposure. Indigo plants require direct sunlight and warm temperatures to thrive during the growing season. The minimal growing temperature is around 67 degrees Farenheit, but the plant will do better in temperatures that are 70 to 80 F.
Prepare a garden bed by mixing sandy, loamy soil mix into the topsoil of the garden. Indigo plants thrives in slightly alkaline soil but can also tolerate neutral or slightly acidic soils. Soil must be well-drained.
Plant indigo plants 4 to 5 feet apart in the early evening and water the soil until thoroughly moist. Water once each day for the first two weeks until the plants become established.
Do not fertilize indigo plants. As a legume, indigo plants can absorb nitrogen from the air and grow well in nutrient-deficient soil.
Water indigo plants once every two days during the growing season and only when the soil is dry to the touch during the winter if the indigo is being grown as a perennial. Water well with a hose until the soil around the indigo is thoroughly moist.
Growing Sesame Plants from Seed
Sesame seeds should not be direct sown outdoors. Plant seeds indoors four to six weeks before the last frost date.
Lightly cover with soil-less planting mix. Keep moist until they germinate, then water once a week or so.
Sesame seeds germinate best at temperatures between 68 and 75 degrees. They are indeterminate plants, which means they will continue to bloom and set seed capsules over a long period in the summer, with peak flowering in July and early August.
The Dark History of Indigo, Slavery's Other Cash Crop
There was a time, not all that long ago, that if you wanted your toga or whatever to be a different color, you'd have to go find something in nature to dye it with: maybe mud, maybe an insect, or the seed, flower, root or leaves of a plant.
Color Before Chemistry
Before 1856, when a teenaged British chemist named William Perkins accidentally formulated the first synthetic dye while trying to find a cure for malaria (he produced mauveine, which was an intense purple color), harvesting natural resources for dyes was a big deal.
"Until Perkins' discovery, anything that had color — clothes, shoes, rugs, tapestries — was dyed with either a plant, a bug or a mineral," says Donna Hardy, the president and founder of the International Center for Indigo Culture.
Perkins discovered the means of making purple cheaply and in large quantities — before that, purple dye was very precious the most reliable source was to extract it from the dessicated mucus gland of a sea snail. Blue was easier to come by, and useful because it could be mixed with other colors to make purples and greens, but before the advent of synthetic dyes, getting pigment out of the land was laborious.
To make anything blue, you needed indigo, an organic compound found in the leaves of certain plants — most notably indigo plants in the genus Indigofera (from India or South America), although other plants such as woad (Isatis tinctoria) contain indigo compounds, too — just in much lower concentrations. The first Indigofera used by Europeans was grown in the Far East (the word indigo comes from the Greek word for India). Indigo was highly valued in the West, but Europeans wanted their own source of indigo that wasn't so expensive. That's where the New World came in.
Indigo in North America
Until indigo dye was synthesized in Europe in 1882, a species of Asian Indigofera was a huge cash crop wherever it could be grown.
"In the 1600s, Europeans colonized North America, and immediately started trying to grow crops of economic importance," says Hardy. "Indigo is one of the first plants the British attempted to grow when they got to North America. They tried growing it in Jamestown, the Dutch tried it in New Amsterdam — present-day New York City. The French had some success in Louisiana, but nobody had much luck until Eliza Lucas came along."
In the 1730s, 16-year-old Eliza Lucas, whose father was lieutenant governor of Antigua and who had an interest in botany, was put in charge of three of her father's South Carolina plantations. She and her father had no idea what to grow there, but he sent her seeds from Antigua, and indigo seemed to Eliza to have the most promise. She married a man named Charles Pinkney who wrote down the instructions for how to grow and process indigo, and after a while they made enough seed to hand out to the neighbors, which started an indigo bonanza in the Southern colonies.
Indigo and Slavery
"Before indigo, rice and deer hides were the main exports from Charleston," says Hardy. "Native American slaves were the first export."
Of course, Eliza and Charles Pinkney didn't figure out how to grow and process indigo — their slaves did. The import of African slaves began to ramp up in the southern colonies as a result of the indigo boom in the mid-18th century. In fact, one of the biggest indigo promoters of the time, Moses Lindo, who went to Charleston from England to act as inspector general of indigo coming out of the Port of Charleston, owned a slave ship called the Lindo Packet, with which he imported enslaved people from Barbados to Charleston. And the indigo fever and the dependence on slave labor that came with it didn't end in South Carolina.
"Slavery wasn't even legal in Georgia until indigo became the main export in South Carolina," says Hardy. "The [British] governors in Georgia decided to legalize slavery to keep the indigo industry going."
Georgia's ban on slavery ended in 1751, and by the beginning of the Revolutionary War 15 years later, the enslaved population of that state had grown to over 18,000. Though the American colonies winning their independence from Britain tanked the indigo market, it was quickly replaced by rice and cotton. For its part, England turned its attention to India for its indigo needs, where British colonists forced sharecroppers to grow indigo for hardly any money. The legacy of slavery followed indigo around until it was replaced by synthetic indigo in the early 20th century, when it slipped into obscurity.