Text: Ashley Walker and Susan Dye copyright 28th July 2020, updated 31 July 2020
Header photo copyright Isabella Whitworth, showing three varieties of Japanese Indigo

Warning: This post contains tentative information about the names of Japanese Indigo Varieties. Clarifications most welcome!

A few people, including myself, have been comparing varieties of Japanese Indigo to see if they produce the same amount of indigo. For example see:

• Isabella Whitworth, Devon, UK  Dyeing with Japanese Indigo
• Ashley Walker, Hitchin, UK  Three strains of Japanese Indigo tested and observations on indigo extraction
• Kathy Nelson in Oregon USA. See comment at bottom of Japanese Indigo and Seed Dormancy
• Leena Riihelä at Riihivilla  See also here

The results of Isabella’s experiments and our own are important for the natural dyer as they show that there are significant differences in the amount of indigo produced by different varieties. However this knowledge is not much use without accurate identification and naming of variety types. Until very recently most Japanese Indigo seeds have been sold without varietal names making it almost impossible to know what you are getting. Even now Japanese indigo grown around the world by craft dyers has not been properly correlated with the original Japanese varieties. I have read that there were around 20 different Japanese Indigo varieties growing at one time in Japan. Each variety was adapted to particular environmental conditions and growers’ requirements.

The only publication I can find which talks about Japanese Indigo varieties came to light in a social media post by Luisa Uribe from Indigo Bluefields. This is a Japanese childrens book about Indigo.
Indigo Picture Book (アイの絵本) by Sachiko Nishina and edited by Kusakabe Nobuyuki (くさかべ のぶゆき) . It contains pictures of 4 varieties of Persicaria tinctoria (Japanese Indigo).

1. Red flower Kojōko (こじょうこ あかばな)
2. White Flower Kojōko (こじょうこ しろばな)
3. Hyakkan (ひゃつかん)
4. Red Stem Senbon (あかくきこ せんぼん)

My own attempts to link these names to the varieties we grow are frankly dismal as it’s been impossible to trace their origins.

The round or broad leaf variety which I grow originally came from a natural dyer in the USA Pallas Hubler. None of the photos in the book show plants with rounded leaves so the identity of this variety remains a total mystery. The intermediate white flowered variety was from Teresinha Roberts at Wild Colours via George at Bailiwick Blue in the Channel Islands. This closely resembles the descriptions of “Kojōko” (I have seen a number of different spellings of this) so this seems a likely match. The third variety “Long leaf” is from Rühlemann’s in Germany. This variety has a tendency for its leaves to curl at the edges. It could be “Hyakken” but George at Bailiwick Blue thinks “Senbon” is also a strong possibility.

This year I received seeds from a fourth source, via Italy from Japan (see photograph below). This pink flowered variety is also un-named but has larger pointed leaves resembling those of the white-flowered variety. This is a more likely candidate to be “Senbon“. Overall, it seems likely that flower colour is not an important differentiator between some of the varieties. There are reports of both white and pink flowered “Senbon”. “Kojōko” can also come in the two colours.

Japanese words for Indigo

Tade-ai – Tade ai is a general Japanese name for Japanese Indigo. “Ai” means indigo (as well as love or affection) and the first word is a descriptor. Tade is the name of another Persicaria species Persicaria hydropiper or Water Pepper, a Japanese culinary herb. Tade is also a general name for the Persicaria family (Knotweeds or Smartweeds).

“Ryūkyū-ai” The name originates from the Ryukyu Islands of Japan, of which the best known to westerners is Okinawa. These islands to the far south of mainland Japan enjoy a sub-tropical climate. I came accross the name from comments by Scharine Kirchoff at Ryukyu Heritage Textiles who uses this plant in her work. It develops dark blue-ish purple leaf veins when ready to harvest and sounds very exotic. This is not Persicaria tinctoria but an entirely different plant called Strobilanthes cusia. Dominique Cardon gives its common name as Rum or Assam Indigo.

A further snippet of related information from Brittany Boles’ Facebook page Indigo Pigment Extraction Methods. talks about a variety of Persicaria tinctoria grown by Two Looms Textiles in Omak, Washington State in the USA. Adam, the grower, obtained what he calls “Okinawa Crinkle” from the Ryukyu Islands in the hope that it would flower earlier in the year than his main crop of “Kojōko” which does not have time to set seed before the winter at his latitude.

“Yama-ai” mountain indigo. Mercurialis leiocarpa also found growing in Japan and the Ryukyu Islands. This plant is closely related to UK native “dog’s mercury” Mercurialis perennis (which is poisonous just in case you get tempted). The leaves or juice was rubbed directory onto fabric giving a light green-blue colour known as suri-ai (rubbed blue). The dye contains impurities and the proportion of colorant is low, so the dye-colour was dull and ran easily (see here).

Please Help

I am frustrated by hunting around for vague snippets of information and would welcome with open arms any comments that correct or shed light on the rather dubious collection of ‘odds and ends’ I have collected here. Thank you to those who have already contributed their insights.

A note on plant varieties

In nature, varieties are different forms of the same plant species which breed true, i.e. if two plants of the same “variety” cross-fertilise, the offspring will be much the same as the parents. However, if grown close together two different varieties are perfectly capable of interbreeding. Varieties are formed when isolated populations start to evolve away from each other and are sometimes classified as a sub-species. Varieties can also be produced by human selection. Careful breeding by commercial growers produces most of the named varieties of plants sold by garden centres and agricultural suppliers. There is no need for the craft dyer to get hung up about the term ‘subspecies’. Think of it like an accolade which a naturally occurring variety gets given (a form of celebrity status) which commemorates the eagle-eyed botanist who first identifies it.

At Natures Rainbow we grow the three varieties shown in the header photograph, usually separated by a minimum of 2 metres (we only have a small growing space). In our experience each of the three varieties breeds true (consistently produce offspring that resemble the parent). And, after three years of growing all three varieties within 2m of each other (socially distanced?!) I have not seen any “hybrids” from cross-fertilisation even though it is definitely possible. I suspect therefore, that the plants’ main propagation method is via self-pollination rather than cross-pollination. Bees and other pollinators love the flowers so they must be carrying pollen between the plants. So if any of you out there want to breed new varieties, my guess would be that you’ve got to work out a method of artificial pollination.