Category Archives: woad

The traditional medieval dyeplant of northern europe for blues

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

Seeds of Colour

seedlings 4

Japanese Indigo seedlings on our windowsill

So far this month the weather here is how I remember April from childhood: sun and showers and no extremes of heat or cold. And I’m feeling enthusiastic about the growing season ahead.

We’re now well into the annual cycle of seed propagation. The windowsill in our front room has trays of Dyer’s Chamomile, Dyer’s Coreopsis, Japanese Indigo and a bee-friendly Dahlia. With the exception of the Dahlia, all these seeds are saved from previous years.

Japanese indigo needs a slightly longer growing season than our climate can offer. So we start seeds off in heated trays on our sunniest windowsill in late February or March. A home-made rig provides extra light for the plants during gloomy weather. From here, they move on to a cold frame in the back garden or the unheated greenhouse. We won’t plant the Japanese Indigo out until all risk of frost is past.

Dye plant seedlings indoors

Dye plant seedlings indoors

Cold Frame near the house

Cold Frame near the house

In case you’re curious, we collect Woad seeds in early summer to prevent them spreading everywhere and sow direct into the soil the following autumn or spring. Weld (biennial) and Dyer’s Greenweed (perennial) are reliable self-seeders and not invasive, so we let these grow where they will and don’t usually bother planting them up in seed trays.

These last two photographs show the end of one cycle of indigo and the start of the next. I was amazed at the beautiful patterns in the mould on top of a forgotten Japanese indigo vat. For a plant dyer at least, there’s no happier sight than trays of lush green Japanese Indigo seedlings!

Patterns of mould growth on a forgotten indigo dyebath

Patterns of mould growth on a forgotten indigo dyebath

A good germination rate. A dyer's delight!

A good germination rate. A dyer’s delight!

It began with blue

blue fleece small

Therapists say that blue is connected with communication, so it seems apt to start with a post about woad and Japanese indigo. These are the two easiest indigo-bearing plants to grow here in the temperate climate of the South East of England. We grow both of these on our allotments each year.

It’s easy to save seed from woad and the plant is hardy in our climate. Anyone can grow it.

Japanese indigo iBLUE seed saving indigos much harder from a horticultural point of view. It’s not frost hardy and is prone to pests when over-wintered under glass. Our growing season is just a bit too short for seeds to set reliably in any quantity. But it yields a lot more indigo than woad. One of our ‘labours of love’ is picking the tiny seeds from dry flower heads at the end of each season to ensure we have plants for the following year.

When it comes to creating a woad or Japanese indigo dye vat there really is no substitute for learning alongside someone more experienced.

I remember the acute disappointment years ago when our first crop of woad leaves gave no trace of blue whatsoever, despite extensive reading and the enthusiastic help of our local Spinners, Weavers and Dyers guild. My partner Ash does not show his emotions much. But there was no doubt that evening just how angry and frustrated he was. We later came to realise the problem had been that we were using an ineffective reducing agent, although it was the one recommended in a leading text book. (There’s an entire post to be written on the subject of the errors and ambiguities I’ve encountered in books about plant dyeing.)

Over the following years we have refined our plant dyeing techniques enormously. Some of our current practice has evolved out of our own experiments. But just as much has come from attending workshops with wonderful teachers, in particular Jenny Dean, Penny Walsh, Jane Meredith and Debbie Bamford. The Weavers Spinners and Dyers Guilds are an excellent learning resource and way to connect with like-minded craftspeople.