Sustainable Cultivation of Plant-derived Indigo for Diversification and On-farm Value-added Dye Pigment Production

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2010: $9,871.00
Projected End Date: 12/31/2011
Region: Southern
State: Tennessee
Principal Investigator:

Annual Reports


  • Miscellaneous: Indigo


  • Crop Production: biological inoculants, nutrient cycling
  • Education and Training: farmer to farmer, on-farm/ranch research, workshop
  • Farm Business Management: new enterprise development, cooperatives, budgets/cost and returns, value added, agritourism
  • Pest Management: mulches - living, mulching - vegetative
  • Production Systems: general crop production
  • Soil Management: green manures, soil analysis


    A comparison of indigo yielding plants showed that varieties of Indigofera tinctoria, Indigofera suffruticosa and Persicaria tinctoria can all be grown in Middle Tennessee. The I.tinctoria and I.suff were both difficult to germinate in greenhouse starts and difficult to direct seed, resulting in fewer established plants in our study. Initial indigo extraction data for P.tinctoria indicates a range of variables impacts final pigment color, including growing and processing conditions and stress conditions during plant growth. Preliminary dried indigo quality results in successful pigment extraction batches showed approximately 2-3% indigotin content, although more research on successful growing and processing is needed to yield consistent results.


    Natural dyes are plant and earth-based materials that can be used for dyeing textiles, foods and other industrial uses. In addition to the use of fresh plant material, there is a market for both dried plant madder, or powders and concentrated dye liquors made from fresh dye plant material, whether leaves (indigo), flowers (marigold, weld), or roots (madder). These storable, easy to ship materials are becoming increasingly popular among home dyers due to their safety, ease of use and environmentally friendly characteristics. We believe that with the appropriate processing, the plants can be turned into commercially viable extracts for industrial dyeing. In addition to providing a source of year-round income, natural dye crops can increase sustainability in a diversified cropping system, by increasing leguminous plants, beneficial insect habitat, and perennial crops. Thus, they are a potentially viable cash crop for Tennessee growers.
    However, in order to move natural dye crops into the wider market, including commercial and industrial applications, we must find cost effective and logistically feasible ways to grow and process the plants into a value- added pigment or extract form. In order to increase the customer base for natural dyes, we must determine the best ways to turn raw plant material from the agricultural commodity into an easier to use industrial pigment. This includes an investigation of how to produce the raw plant material so the yields of pigment are highest, as well as determining the optimal processing techniques. Finally, in the case of direct sale of pigment or dye to artisan or craft customers, it may be important to the growers to have appropriate technology to allow for on-farm processing, allowing for farm to dye traceability so end consumer may be able to know which farm grew their dyes. Small scale processing has been shown to be economically viable in many agricultural industries where product differentiation is important, such as specialty cheese processing. While there may be a small local market for fresh dye material, without the processing stage we expect the market to be greatly limited, as well as season limited instead of year-round.

    The focus of this SARE study was on plants containing blue dye pigment, or Indigo-containing plants. In our past experience, several indigo-containing plants are low nutrient feeders and have few pest problems. For example, the indigo-containing plants in the Indigofera species are leguminous plants that frequently serve as a green manure and a summer cover crop in the tropics due to their nitrogen-fixing capabilities. A major goal of our research was to determine if these nitrogen-fixing indigo plants can be successfully grown in Tennessee.

    Increasing crop diversity through natural dye plants also allows growers, especially those with diversified vegetable cropping systems, to capitalize on different farm labor throughout the year. Most of the dye crops offer once or twice-a-year harvests instead of the few times a week harvests as market vegetable production can require. Indigo, for example, can be harvested in July and October in Tennessee if seedlings are established by Spring. Potential methods for processing include a fresh leaf precipitation method (the subject of this study) which takes 2-3 days and a dried leaf composting processes which can take up to 100 days and is labor intensive without specialized equipment. The dye precursor for indigo is found in the leaves or leaflets.

    There are currently 3 varieties of commercially grown indigo plants, including Indigofera spp, Persicaria tinctoria (Japanese Indigo, formerly called Polygonum tincotirum, Ai species), and Isatis tinctoria (woad). The blue indigo pigment shows perhaps the most potential because of its recognizable blue shades and the fascination value of the story behind indigo and thus was the subject of our research. In addition because of the complications of processing the plant it has the least information available to growers.

    Selling indigo processed into a high quality and consistent extract to the commercial manufacturing sector (dyehouses) would likely be the largest potential market in terms of volume. This market is not yet developed but there is believed to be an interest, especially among manufacturers looking for an eco-friendly or domestic source of dyes.

    In addition to selling into the industrial pigment market, there is likely a more immediately accessible market for dyes among artisans and craftspeople. In an Internet-based retail setting, unbranded, conventionally grown (non-organic), natural indigo powder currently sells for between $46 (The Dyeworks, CO) and $60 (Earth Guild, NC) per pound. Research suggests yields of 60lbs/acre of indigo yield for Indigofera species, thus garnering between $2760 per acre and $3600 per acre of indigo after processing. However, an Italian research project in a climate more similar to the Southeastern US shows yields of up to 326 kg/hectare, or 290 lbs/acre of Indigo from the Persicaria tinctoria (Angelini, et al. 2004). This would result in approximately $13000/ acre. According to a 2004 European Union endorsed research team called the Spindigo Project, woad can produce indigo in quantities of approximately 50 kg/ha or 44 lbs/acre. Woad powder currently retails on the internet for 40g/25 euros (Bleu de Lectoure) or 20.50 British Pounds for 20 g (Woad-inc). These sell for much higher than we think our market could currently bear in the Southern US, at an equivalent of $635 per pound (given a 1.4 Dollar to Euro Exchange rate and marketing in very small quantities), which would garner $27,966 per acre for woad. These extremely high value products are the result of branding, marketing and EU customer desire for the historic dye of their region. The indigotin (pigment) concentration of woad is only ¼ that of the Indigofera species, making it less productive from a yield of pigment per acre basis, and so it was not included in our study. However, it does show how small farms or a cooperative of farms can be profitable in this niche market with the right branding and a willing market.
    As an example of a premium going to a branded, naturally dye extract, Woad-Inc a British company selling locally-grown woad pigment, sells pigment in quantities of 20 g for $20.50GPB, or $34 USD. This is equal to about $2.64/g compared to the average price of unbranded indigo pigment selling for approximately $60/lb (454g), or approximately $0.13/gram for the commodity (Table Rock Llamas, Colorado). The Woad-Inc. product is not certified organic since it uses a pre-emergent herbicide, but the marketing of the product does focus heavily on the story behind the one farm that grows the crop.
    There are currently branded natural dye extracts grown in France (Couleurs de Plantes), England, (Woad-Inc), India (Colors of Nature), and several other small scale projects around the globe, with US natural dye distributors carrying these lines. However, there is no US grown or sourced line of natural dyes sold at any appreciable volume.

    There is a long history of indigo growing in the South United States. Indigo was one of the top three exported cash crops in the 1700s. We know from historical research that three varieties of Indigofera were commonly grown in the deep South: Indigofera caroliniana Mill, I. tinctoria L (French indigo), and I. suffruticosa Mill. (Guatemala Indigo). Most indigo production throughout the 16th and 17th Century Colonial America occurred in South Carolina plantations, where it was found on dry high ground. The amount of indigo exported from South Carolina increased from 138,118 pounds in 1748 to 1,107,660 pounds in 1772, shortly before the American Revolution, mostly for export to England for fabric dyeing. During this time, Georgia exported 55,380 lbs. The first synthetic dye, isolated from a coal-tar, was created in 1856 and rapidly synthetic versions replaced the market for natural color compounds, as well as the amount of indigo and other natural dyes grown in the US and abroad. However, the beauty and vibrancy of natural dyes cannot be replaced and it is our belief that the emerging environmentally-aware fashion industry will desire and purchase sustainably-grown natural dyes rather than the petroleum and coar-tar derived synthetic dyes currently used in industry.

    Project objectives:

    Southeastern growers need research to determine suitable natural dye crops for our region, and to establish best practices for cultivation and processing of these plants. This project’s goals were to provide a baseline of cultivation, production and cost data for working with the three most promising indigo-containing plants specifically tropical indigo (Indigofera suffructosa and Indigofera tinctoria), and Japanese indigo (Persicaria tinctoria) to create storable, value-added dye products that can be sold from the farm-gate across the region as a natural alternative to synthetic indigo. In addition to assessing the production techniques that yield the highest quality pigment, we made some preliminary post-harvest handling and processing assessments. We explored techniques for on-farm processing of indigo-containing plants into both powdered natural indigo and indigo ‘sludge’.

    The ultimate goal of this research project was to establish which indigo-containing plants will grow best in our region of Middle Tennessee, and how they may be best processed to yield products of high market value. Another initial objective was to determine what the best conditions were for growing the different varieties. We planned to measure green harvest weight per variable condition to asses overall green plant yield. We then sought to isolate the pigment from the indigo plant matter through the precipitation method and measure overall sludge weight, dried weight of precipitate, and percentage indigotin content in precipitate. Our goal was to determine whether indican-containing plants can be grown and are likely to be profitable and successfully grown in our region. We also worked to standardize our processing technique to determine the way this project can be scaled onto other farms without specialized processing or cultivation/harvesting equipment.

    The research trial involved growing and processing 100 row-feet of each of the three variables of the three indigo varieties utilizing organic practices. Where applicable, we used varying fertilizer/nutrient input variables. We wanted to determine the most suitable methods for cultivating the selected crop(s), based not only on green vegetative yield but also isolated pigment yield after extraction of the indigo pigment. Indigo’s market value is in powder form, so the weight and purity of indigo pigment is ultimately the most important thing. By investigating different nutrient regimes, we sought to determine maximum profitability based on the volume and purity of final product (pigment) yield after taking into account input costs.
    Following our 2010 growing season in which Indigofera had very poor germination, we decided to extend our grant time frame for one year and run a small seed germination trial to add to the final report. In Spring 2011, we ran two I. tinctoria germination trials to determine the best strategy for starting Indigofera species from seed, one in March and one in May. The trial has heat, scarification, and soaking variables for the seeds so we can find out the best means way for starting these seeds. Seed starting trails for I. suff. was not possible because all of the seed suppliers were sold out for 2011.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.