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Persicaria tinctoria

Three strains of Japanese Indigo tested and observations on indigo extraction

An article by Ashley Walker
© copyright 2017

This year I had planned to carry out a tightly controlled experiment to look for variation in the amount of indigo produced by three fairly distinct strains of Japanese indigo. However due to a prolonged and still undiagnosed illness, my plans were thwarted and the experiment did not work out quite as I had hoped. However, on 12th and 13th October 2017, with help from Brian Bond another keen plant dyer, I did manage to complete a test of the three plants although the results are not directly comparable due to different planting times and maturity of each variety.

The strains

Round or wide leaf indigo

Persicaria tinctoria

Round or wide leaved Indigo. Directly sown bed

Grown from seed originally from the USA (from fellow natural dyer Pallas Hubler in Washington State on the west coast) who sent a few seeds over to Brian in 2013. We have been growing and saving seed from this strain ever since so it is possible that it has become adapted to growing in our soil.

  • Late flowering (October into November)
  • Pink Flowers
  • Compact short flower stems
  • Wide short or rounded leaves
  • Foliage pale to mid green
  • Easily damaged by high nitrogen levels in the soil. Grows poorly in cool overcast weather.

Long leaf indigo

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Long leafed Japanese Indigo in full flower.

Seed for this was obtained from the German supplier Rühlemann’s. Unfortunately this was in full flower by the time I was able to harvest it for the test and from previous experiments I know that once indigo has committed itself to flower production the amount of indigo in the leaf falls dramatically.

  • Large long pointed leaves
  • Pink flowers
  • Long delicate flower stalks
  • Early flower (September-October)
  • Dark green leaves
  • Very tolerant of high nitrogen in the soil and generally more robust.

An in-between white flowered strain

Persicaria tinctoria

Intermediate white flowered Japanese Indigo

The seed was obtained from Lisa George Fukuda a fellow plant dyer in Guernsey who had it originally from Teresinha Roberts at Wild Colours

Unfortunately this was planted out late in the year (August) so as yet I know little about its habit as there has not been enough time for it to grow to full maturity.

  • Longish leaves
  • White flower
  • Easily damaged by high nitrogen fertilizer.
  • Mid green leaves
  • Quickly bushes out, highly branching.

All three strains were grown on the Natures Rainbow allotment in Hitchin in a chalk soil with a strong application of Fish, Blood and Bone plus some chicken manure pellets.

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Leaves from all three strains.

Persecaria tinctoria

Rounded leaf Japanese Indigo growing with the Long Leaf strain in the greenhouse. Here they look like two completely different species.

The experiment

After stripping the leaves from the freshly cut indigo stalks, 220g of leaves from each strain were slowly heated from room temperature to 80°C in stainless steel pans with 4 litres of tap water. The pans were stirred at short intervals throughout. Note: the weight of leaves was determined by the amount of the long leaved strain that I could harvest from shoots that had not yet come into full flower as I wished to minimise the effect of flowering on indigo production. The amount of water in the pans was deliberately large as I wished the final colour to be on the pale side as variations in pale colours are easier to distinguish. More water also means the pot is easier to stir before the leaves are cooked.

Heating to 80°C took about 35 minutes. The pans were then taken off the heat and allowed to cool, free standing in the air for 1 hour. (The air temperature was appoximately 20°C).

Persicaria tinctoria

Intermediate Japanese Indigo extraction bath with container of liquor to show gray colour. Photo taken just after pan was removed from the heat.

At this point no difference could be noticed between the different pans. The liquor in each pan being a pale greyish blue in each case.

After one hour the leaves were removed by straining through an old pair of tights into a large plastic bucket. Half a cup of household ammonia was then added to the liquor. Taking care not to breathe in hot fumes, this liquor was poured back and forth from bucket to pan 10 to 15 times to aerate and oxidise the indigo precursor to indigo. The colour of the liquor changed from grey to yellow green, with the round leaved plant giving the darkest colour change and the long leaved plant the least. This is a good indicator of how much indigo is present in each pan.

Once oxidised to indigo, the liquor is now in a stable form and can be left for long periods without any loss of indigo. The reduction vats (indigo dye baths) were set up the following day as follows. The pans were heated to 50°C, one level teaspoon of Spectralite (Thiourea Dioxide) was added to each pan, gently stirred in and left for 30 minutes for the indigo to reduce to its soluble form. Identical weight skeins (26g) of wool were added to the baths at 50°C and left for 20 minutes before removal and oxidation in the air. The dye baths were kept in a hay box to maintain constant temperature during the dyeing.

The results

Japanese Indigo

First results showing a surprising difference in colour obtained

The long-leaved plants (left) were disappointing only producing an ice blue colour. The white-flowered intermediate-leaved plant gave a slightly deeper shade but still pale (centre). The round-leaved plant produced a respectable light blue (right).

The poor results for the long-leaved plants was understandable because of their flowering state, however I was surprised the colour was quite so pale. The good results for the round-leaved plant was a real surprise as I had become convinced these plants would not be the best. Overall the pale colours made me worry that I had not optimized the process and I decided to repeat the experiment for the round-leaved and intermediate-leaved white-flowered plants (I had no more of the long-leaved plant so I could not replicate this one).

On the second run I made one change which was to slow the cooling of the extraction bath after reaching 80°C by placing the pans in hay boxes. For this experiment, using 4 liters of water I was aware that this small amount of liquor would cool quickly, perhaps too quickly? An experiment we conducted some years ago revealed that premature cooling of the extraction bath resulted in a dramatic loss of indigo when processing woad leaves. Two years ago we discovered that leaving the bath at a high temperature for more than one hour also results in a loss of indigo so I have become wary of putting large baths in hay boxes which are capable of maintaining a high temperature for hours.

In this second run the results from the white-flowered intermediate-leaved plant improved but the round-leaved plant still produced the better result (which itself was no better than in the first run).

Skeins of wool dyed with Japanese Indigo

Second run with intermediate white flowered indigo plant compared to rounded leaf plant.

Skeins of wool dyed with Japanese Indigo

Comparison of intermediate white flower strains. The difference between quick and slow cooling of the extraction bath.

Wool dyed with Persicaria tinctoria

No real difference between runs for the Rounded leaf strain.

Discussion

In theory all three plants should have produced broadly similar amounts of indigo. That they did not could have been due to genetic differences but as noted above all three plants were at different stages of development having been planted at different times and the round-leaved strain had possibly adapted to the local soil over the 4/5 or so years I have been growing it. The poor results from the long-leaved plant may have been entirely due to their flowering state. The intermediate-leaved white-flowered strain had only been planted out in late August and may not have had sufficient exposure to the sun to develop much indigo.

The diversity of results shows how critical it is to grow and harvest the plant at the right time. I was certainly concerned that harvesting the plants in October was a risk, as all three varieties were producing flower buds (although only the long-leaved plants were in full flower). Later I extracted a concentrated bath of indigo by making up a large pan crammed full of leaves and only enough water to barely cover the leaves when they were pressed down forcibly. The results were pleasingly strong indicating that the leaves were still fully charged with indigo.

Skein on right dyed with a strong indigo dye bath

Skein on right dyed with a strong indigo dye bath

I will certainly be making strenuous efforts to continue to save the seed from the round leaf strain whatever the reasons for the underperformance of the other two strains!

Thanks to:

Brian Bond
Lisa George Fukuda
Pallas Hubler

Indigo dyed wool

The range of blues obtained from the three strains of Japanese indigo.

Persicaria tinctoria

Growing Japanese Indigo

An article by Ashley Walker
© copyright 2016

Japanese Indigo, Persicaria tinctoria or Polygonum tinctoria is a frost tender member of the knotweed family. Originally from China and Vietnam it likes to grow in warm moist climates, often as a waterside plant. Our closest relative in the UK is Common Bistort or Persicaria bistorta which closely resembles Japanese Indigo but has no trace of indigo in its leaves (I did try once) though it does give a pleasant orange on alum mordanted material. Japanese Indigo will grow from seed to flower in one season and, if it does not get frosted, is capable of growing into the second year though here in the UK getting a plant through the winter is very difficult even indoors with extra lighting. We grow Japanese Indigo because it gives more indigo than Woad (approx. double the amount) and the colour is generally cleaner and more predictable than Woad.

Varieties of Japanese Indigo

There appear to be two distinct varieties though I have not seen anyone put a name to them.

Persicaria tinctoria

Pointed Leaf Japanese indigo

Pointed leaf Japanese Indigo. This is grown as an indigo dye crop in Germany and may have been selected for its ability to grow in a northern climate. It has pale green stems and white or pale pink flowers. The leaves are narrow and pointed.

Persicaria timctoria

Round Leafed Japanese indigo

Round leaf Japanese Indigo. This is the variety most commonly grown in gardens, perhaps because it produces a profusion of pretty deep pink or white flowers. Its stems are thick and also have a tendency to be pink. It seems less adapted to a northern climate and in poor weather struggles to grow – when first planted out, the leaves often go pink or yellow at the tops of the stems and continue like this if growth is slow. When grown in a greenhouse or polytunnel however the plants are greener, although I have not noticed any difference in indigo production between the two.

Growing Japanese Indigo

Persicharia tinctoria seedlings

Some of my seeds are “tricotyledons” and these germinate with 3 baby leaves rather than the usual 2. This is an uncommon mutation and may be a sign of inbreeding.

The shiny black seeds have only a short life (about a year if stored in a cool dry place). They can be frozen in the freezer and will last longer. To freeze the seeds first dry on a windowsill then place in a sealed plastic bag with a packet of silicon desiccator for a few weeks then pop in the freezer. Note: seeds frozen in this way tend to germinate slowly and may take up to 5 or 6 weeks to germinate. Commercially bought seeds are often stored frozen so don’t be too alarmed if you get no germination’s in the first 2 weeks. Interestingly I tried drying some seeds with a hair dryer on a low heat setting from a distance and found that this treatment also put the seeds into a deep sleep.

So, using some fresh seed grow in heated seed trays indoors from early April or late March. Sow thinly and cover with a thin layer of compost. Once germinated try to give them as much light as possible as they will grow “leggy” if kept on an average windowsill. The seeds should germinate readily within two weeks but occasional seeds may not germinate for a month.

Persicharia tinctoria seedlings

Seedlings with secondary leaves at around 4 weeks

The plants are very robust and rarely succumb to disease or pest, they will also transplant readily and can be pricked out at an early stage and potted up if you wish to do this. I usually leave them to grow in the tray until I am reasonably sure there will be no more frosts. Here in Hertfordshire that’s usually around the 6th May. By this time the plants will be quite large and the trays root-bound, some of the plants will have put out secondary roots from the stems and rooted in more than one place. Separating the plants out is therefore difficult and it is best to soak the tray in a bucket of water before trying. Do not worry about breaking the roots as Japanese indigo will re-root itself with ease. Planting in May is only advantageous if the forecast is for warm and sunny weather. If the forecast is for cold overcast weather wait until June before planting out.

Dye plants waiting to be planted out

Trays of dye plants waiting to be planted out including some root bound Japanese indigo.

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These plants stayed much the same size for 2 months before finally starting to grow in August of 2016

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These Japanese indigo plants were mostly planted on the same patch of ground as last year and only the plants to the rear of this bed were planted on fresh soil. All the plants were equally manured.

Weather is critical for good plant growth as you must remember this is a semi tropical plant. Sometimes the weather never really becomes ideal, in the cool dark summer of 2012 the plants grew hardly any larger than when I put them out. The plants were pale and looked sickly and there was no harvest. This year (2016) many of the plants also grew very slowly because the weather in the early part of the season was cool, wet and cloudy. It was not until late July when the weather improved that they really started to grow. If you have plenty of seedlings you can plant them about 4 inches apart in a heavily manured soil. Both Woad and Japanese indigo require lots of feeding to get a decent sized plant. Manure is the best if you can get it, but other fertilizers will do. Soil type is not much of an issue and the plants will grow on any soil. Clay loams are probably the best. My plants are grown on a poor chalk soil and I have problems with some nutrients in the soil being used up very quickly. Crop rotation is important for me as the plants do not seem to grow well if planted in the same area as the previous year. All my indigo beds need to be given a second feed in August particularly if I cut a first crop and allow the plants to regrow. Even so, many plants regrow with yellow leaves indicating they are short of some vital nutrient.

Persicaria tinctoria roots

Roots grow readily from the stem nodes.

If you only have a few plants and want to grow more from cuttings you are in luck as Japanese indigo is one of the easiest plants to grow this way. Just cut off the stems from about 6 inches above the ground and place in a container of water. New roots will grow immediately from the stem nodes and the cuttings will be ready to plant out in two weeks. Alternatively just stick the cuttings directly into the ground and water well (each day in hot weather) until the new plants are established.

Maintenance and harvest

As a waterside plant Japanese indigo is used to having its roots in water and it follows that it will grow very poorly in dry well drained soils. In the summer months of June to August I have to water my plants nearly every day because I have a light chalky soil. Once the plants achieve total ground cover they act as a shade and help keep the soil damp but they still need water on a regular basis.

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Take the first cut about 8 inches above ground leaving plenty of leaves on the plant.

This year I grew some Japanese indigo amongst other plants. I was surprised how well it responded to the competition, growing taller and greener. In a good year it is possible to take two or even three harvests of the plant. The stems are cut about 6 to 8 inches above the ground and the plants soon grow back. For an added boost to your harvest once you have stripped the leaves off the stems the now leafless stems can be placed in buckets of water with a dollop of liquid fertilizer and they will also grow quickly back. The stems alone have no indigo content.

Persicaria tinctoria stems

Stems of Japanese indigo after leaves have all been stripped off.

Persicaria tinctoria

The stripped stalks when placed in buckets of water with added liquid fertilizer will rapidly regrow and provide you with an extra harvest.

Indoors or outdoors and growing for seed

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Growing in a greenhouse it was possible to plant the seedlings out earlier but even then a mild frost in early May damaged and killed some of the plants.

 

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Frost damaged seedling in the greenhouse in May 2016.

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Persicaria tinctoria

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Japanese indigo does not need to be grown in a greenhouse or polytunnel unless you live far to the north but it clearly prefers being indoors growing lushly with greener, larger leaves and does not produce flowers until later so has a longer season.

 

 

 

 

 

 

 

 

Japanese indigo needs a long growing season to flower and usually only comes into full flower in October. It is self-fertile so will produce seed in a sealed greenhouse but will flower sooner outside in full sun. However, If frosts or bad weather are forecast before the seed has set be ready to dig a few up and transfer to greenhouse or poly-tunnel or bring indoors in pots. In the North it may be best to grow Japanese Indigo in a greenhouse or poly-tunnel. However, because it flowers later it may not be possible to get seed unless the greenhouse is heated. Some growers have reported that it is possible to get plants through the winter by bringing them into a well-lit and warm area where they will flower early the following year and produce seed.

Persicaria tinctoria

This miserable looking plant flowered in June and as you can see has been highly stressed with stunted growth and pale leaves with a pinkish blush

Persicaria tinctoria flower with honey bee

There are always a few plants that come into flower before the rest and it is best to leave these alone when you harvest. A few years ago I began an experiment to try and breed a variety of early flowering plants so I could be sure of getting some seed even in a bad year. This went according to plan and I ended up with plants that flowered in early September and some in August. However, once the plants start to flower the amount of indigo in the leaves starts to reduce and in full flower the yield is very poor. This led to lower harvests overall. Another strategy you can use for getting seed is to grow a few plants in a dry bed only giving them enough water to keep them alive. These plants will become stressed and will flower earlier – they may look miserable but the seed will produce nice healthy plants next year. Interestingly when the plants are in full flower they are very attractive to bees particularly honey bees. I wonder if honey can be obtained from the German fields of Japanese Indigo, as is possible with the fields of Woad in Norfolk.

Persicaria tinctoriaPersicaria tinctoria seed

Persicaria tinctoria

Seeds from the flowers in the greenhouse. As bees and most pollinating insects could not get into the greenhouse it looks like the the flowers are self fertile.

When the flowers go brown they can be cut and hung up or laid out to dry and some of the seed will fall out. The remainder can then be rubbed out. Separating the seeds from the “chaff” is a skill all by itself. Once you have removed the seeds and dried flower material from the stalks, place the whole lot in a tray and shake from side to side. All the heavy seeds will settle to the bottom and if you are careful you can blow the chaff from the top. This can be a dusty business so you must be careful not to breath it in. Some of the seed will retain an outer layer of brown chaff bound to the seed; this does not impair germination.

Persicaria tinctoria direct dye

Take a few handfuls of leaf and crush them up in a suitable container or blender. Add some white fibre immediately to the mix and leave for an hour. The colour obtained is rather dull and is not wash fast but will give you a good indication of how good your indigo is.

When new to dyeing with Japanese Indigo and Woad it is common to wonder how indigo was discovered as the plants apparently do not produce anything obviously blue though occasionally leaves will die and turn a dark grey or blue black. I suspect that someone observed that when crushed the fresh leaves will release indigo but it is only noticeably blue if you then add some white fiber to them. This is a good test to see if your indigo is ready to be harvested.

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The broken leaf has turned bluish black

Persicaria tinctoria

After the first frosts of the Autumn the upper exposed leaves have been killed and turn a dark bluish black. The indigo has become fixed into the leaf and can only be extracted using a special technique where a reducing agent is applied to prepared leaves.