Tag Archives: Indigo

Isatis tinctoria

Growing Woad

An article by Ashley Walker
© copyright 2016

Woad (Isatis tinctoria) is a naturalised hardy biennial member of the Brassicaceae or cabbage family and was probably introduced into the UK from Europe. There are no close relatives in the UK but there is a similar plant from China called Chinese Woad (Isatis indigotica) which is primarily is grown as a medicinal plant but is also used as a source of indigo. Various web sources including Wikipedia assert that indigotica and tinctoria are botanically indistinguishable. I have recently obtained some Chinese Woad seeds from a German company (Rühlemann’s) so intend to find out the truth of the matter next year. Woad will grow up to four feet high and here in Hertfordshire it flowers in May. The flowers, like so many dye plants, are yellow and make a terrific show in spring.

Unfortunately Woad is classified as a noxious weed in many western states of the US so if you live in one of these states please find out what the restrictions are before you even consider growing it. Here in the UK although it has naturalized and self seeds readily it is not invasive and only tends to grow in disturbed ground. Seeing it in the wild is a rarity. I have been reading about its invasiveness in the US and I now understand that it can invade wild areas of the West with ease probably because these areas are similar in habitat to its native eastern European and Asian plains. It is now classified as a noxious weed in the following states Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. I have not found any reports of problems in the East of the US so would appreciate it if anyone who has any knowledge of this could let me know. Many thanks.
More information can be obtained from this short online document here. For really comprehensive information see here.

Isatis tinctoria seeds

The flat winged seeds of woad contain more than one seed

Woad generally produces masses of large seed “pods or cases” that are only viable for one year. These take a few months to mature and start falling or being blown to the ground by August. The seeds will then start to germinate as soon as the weather becomes wet (inhibitory chemicals in the seed case are washed away by rain). By late October/November new plants will have grown to a substantial size (big enough to harvest). Many seeds will not germinate until the following spring and a few of these will grow and flower in the same year. Those that do, will probably return to a rosette stage towards the end of summer which leads to the unusual sight of rosettes growing at the top of a long stem. Some second year plants will also survive flowering and also return to producing rosettes at the end of summer. These second year rosettes also produce indigo in the leaves.

Isatis tinctoria

Left a smooth edged leaf rosette and right a toothed leaf plant

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Isatis tinctoria

A second year plant that survived its first summer and has returned to the rosette stage (sometimes called a “crown rosette”)

There appears to be a great deal of phenotypic variation between Woad plants. There are big differences in leaf colour ranging from blue/green to pale yellow/green and leaf shape from toothed to smooth-edged. Because of this variability, Woad seedlings can be easily mistaken for weeds at first, especially if they have popped up in unexpected places. However, all Woad plants have a highly distinctive aroma, once smelt never forgotten! It seems likely that plants also differ in the amount of indigo they contain, so there is probably scope for plant breeders to improve the stock.

Propagation

Isatis tinctoria

The long white tap root of a two to three month old young Woad seedling.

Isatis tinctoria

Directly sown Woad bed. Really this bed could have used some thinning out, but it demonstrates that a dense planting will crowd out weeds very effectively.

Woad seeds are only viable for one year so make sure that your seed is fresh. If you buy commercially available seeds there will only be a few tens of seeds in the packet I don’t recommend that you risk them by sowing direct. Sow well away from slugs and snails indoors or outdoors in early April. There is no need to heat the trays. Each winged seed case actually contains more than one seed and so can produce more than one seedling. The plants will grow quickly. Plant them out on a warm day in early May. There’s no need to wait until the last frost as they are hardy.

I have only ever needed to buy Woad seeds once. The plants produce thousands of seeds which will spread around the garden and germinate in mid to late summer. I collect a carrier bag full on a dry sunny day in late summer when the seeds have fully matured. They store well if kept dry. I sow them liberally onto a prepared bed the following April, where they germinate readily and then may need thinning out.

At the beginning, to avoid having to buy the seeds two years running, keep a few seeds to plant in October. Depending on conditions, if you are lucky some of these late sown plants will stay in the rosette stage long enough to providing a useful crop for dyeing in the summer of your second year.

The young seedlings produce long tap roots that can penetrate deep into the ground, so the plants rarely suffer from drought. However watering regularly will encourage growth. The larger the plants the more water they need.

Care and Attention

Isatis tinctoria

Self-seeded Woad

Woad, like Japanese Indigo needs copious quantities of fertiliser to get a good crop. Animal manure is excellent if you can get it. This is best dug into the top few inches of soil before sowing or planting out and will last the whole season. Woad generally does not suffer from many pests and only a few diseases. As a cabbage family plant it may suffer from club root when grown in acid soils, but I have not heard any reports to that effect. When grown densely it does attract the attention of a few species of slug and snail but these seldom threaten the plant’s success so there is little need to take protective action.

Harvest

The amount of indigo in Woad leaves varies according to the weather and the plant’s developmental stage. The plant produces more indigo when the weather is hot and sunny but once the plant has started to produce flower stems in early Spring the amount of indigo in the leaves rapidly diminishes, falling to zero when the plant is in full flower. For this reason Woad is invariably harvested in the summer of its first year while still in a rosette stage. The leaves at this stage are thick, fleshy and give off Woad’s characteristic smell when bruised. The smell is not pleasant but it has such good associations for me that now I have come love it. It is sometimes possible to trick the plants into returning to their rosette stage by cutting the flower stalks before the seeds form. Once harvested, the leaves need to be used the same day. When Woad was grown commercially in the UK the leaves were crushed in a mill and the resulting mass shaped into balls which were then set aside to dry. Woad stored in this way loses some of its indigo.

Further information on Woad and Woad products can be obtained from:

The Woad Centre This is a web site by Ian Howard from Woad Inc the UK’s only commercial grower and processor of indigo from Woad.
A journey into the Blue Article by D.J.Hill
Bleu de Lectoure A Toulouse based company which also grows and produces indigo from Woad.
Isatis tinctoria

 

Isatis tinctoria

Magnificent Woad

Isatis tinctoria

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.

Persicharia tinctoria

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

Persicaria tinctoria

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.

Persicaria tinctoria

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

Persicaria tinctoria

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.

 

Persicaria tinctoria

Frost damaged seedling in the greenhouse in May 2016.

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Persicaria tinctoria

Persicaria tinctoria

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.

Persicaria tinctoria

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.