Woad

Isatis tinctoria

Woad is a plant that was well known to our ancestors in the UK. For many centuries it was the main source of highly prized blue dye, and was traditionally used as a herb for treating wounds and reducing fevers.

Historically, blue was the rarest and the most labour-intensive colour to create. There are various other plants, lichens and fungi in Europe that can produce a ‘bluish’ colour, but for many centuries Europeans relied primarily on woad for a pure blue. Its popularity began to wane with the introduction of the even more vibrant blue of the indigo plant from Asia in the 16th century, and ultimately the advent of synthetic blue dyes in the 19th century sealed its decline.

Woad also has a long history of use as a medicinal plant, both in Europe and in Traditional Chinese Medicine (TCM). There are conflicting opinions over whether the ‘European’ species, Isatis tinctoria is distinct from the Chinese species, Isatis indigotica. The current consensus, backed up by IPNI and WFO, is that I. indigotica is a synonym of I. tinctoria. From a herbal perspective they have very similar properties and are used interchangeably – see uses and benefits below for more details.

The plant itself is a biennial that grows to around 1m in height, producing abundant yellow flowers that are typical of the brassica family. It prefers well-drained soils and full sunshine.

Categories: Herbs, Seed Packs

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Sowing and Growing

Woad seed can either be sown in late summer or in the spring. Late summer sowing produces small plants (or rosettes) that will usually survive outside over the winter unless it is extremely cold; these plants will give you a head-start in the spring and plants that can be harvested in early summer. Sowing in the Spring will delay the harvest until late Summer or early Autumn.

Sow in deep trays or directly into pots. Germination normally takes around 1-2 weeks. When you plant them into their final position in the garden provide a spacing of around 30-45cm between the plants. If you are sowing in the spring, wait until you are confident that the last frost has passed before planting out.

Plants sown in late-summer will flower the following summer. Spring-sown plants usually flower the following year. If you’re not planning to harvest the leaves then be mindful that woad produces a lot of seed that can self-seed and spread if you’re not careful.

As with other members of the cabbage family, woad is susceptible to club root – a soil-borne disease that affects roots, causing them to swell and reducing their ability to take up nutrients. Symptoms of club root include stunted growth, wilting, yellowing leaves. The best way to prevent club root is to rotate annually and avoid planting them where other brassicas have been grown.

Uses and Benefits

Historically, in Europe, the use of woad as a dye was much more widespread than its use as a medicine, whereas in China it was reportedly the other way round. This has changed with the decline of natural dyes and the herbal benefits of woad are increasingly being recognised in the West. In 2011, the root of I. tinctoria was added to the European Pharmacopeia, adding weight to its use in Western herbal medicine and aligning the uses of the two traditions more closely.

In both herbal traditions it was used in similar ways; mainly to reduce inflammation, infections and fevers. Most early European texts focus on its use as a poultice or a plaster, whereas in Traditional Chinese medicine the focus appears to be on both internal and external use. The growing interest in the potential benefits of woad is reflected in the increasing number of studies, especially on its antimicrobial, anti-inflammatory, and antiviral properties.

In Chinese the root is known as Ban lan gen, meaning ‘The Blue Root’ whilst the leaf is called Da qing ye – or ‘Big Green Leaf’. They are used slightly different in TCM; the roots are more focused on antibacterial and antiviral effects, whereas the leaves are used more for their cooling and detoxifying actions.

From a therapeutic point of view its taste is bitter, its effect is cooling, its function is to ‘clear heat, and eliminate toxins’– especially effective for sore throats, fevers and rashes when caused by a virus. Both water and alcohol extracts are used for their antimicrobial, anti-parasitic and anti-inflammatory effects.

Harvesting and Preparation

Harvest the leaf in the Summer shortly before flowering; harvest the root after the first frosts of the Autumn.

Used by TCM practitioners at high doses 9-30g in a decoction for treating acute conditions. For general use at home lower amounts are recommended; typically around 1-2g dried leaf as an infusion per day, or the same weight of root as a decoction.

Alternatively you can make a tincture with fresh leaf at 1:3@50% or fresh root at 1:2@50%, or dried leaf or root at 1:5@40%.

Woad can also be used to make a poultice to help reduce swelling and inflammation, and to harness its antimicrobial properties.

How to make a blue dye from woad:

Materials Needed:

Fresh or dried woad leaves
Water
A pot for boiling
A strainer or cheesecloth
A dyeing vessel (like a bucket)
Fabric or yarn to dye

Steps:

Harvest and Prepare Woad: If using fresh leaves, gather enough woad leaves. If using dried leaves, ensure they are in good condition.
Macerate the Leaves: Chop or bruise the leaves to release the pigment. This can be done using a mortar and pestle or by simply tearing them by hand.
Simmer the Leaves: Place the prepared leaves in a pot of water and simmer gently for about 30-60 minutes. This will extract the dye from the leaves.
Strain the Liquid: After simmering, strain the liquid to separate the dye from the plant material. Use a strainer or cheesecloth for this step.
Prepare the Fabric: Pre-mordant your fabric or yarn if necessary (using alum or another mordant) to help the dye adhere better. Rinse the fabric to remove any residues.
Dye the Fabric: Immerse the fabric in the dye bath, ensuring it’s fully submerged. Let it sit for about 30 minutes to an hour, stirring occasionally.
Rinse and Dry: After dyeing, rinse the fabric in cold water until the water runs clear. Hang it to dry away from direct sunlight to preserve the colour.

Notes:

The colour can vary depending on the concentration of the dye and the fabric used.
Safety precautions are advisable when handling any dyes, including gloves and proper ventilation.

Species Info

Life Cycle

Biennial

UK Native

RHS Pollinators

Can be sown direct?

Yes

Recommended for Beginners

Best for Bees

Soil

Loamy, Sandy

Height

60 – 100 cm

Recommended Sowing Times

April, August, May, September

Alkaline, Neutral

Sunlight

Full sun

Water

Well-drained

Flowering

June, July, August

Hardiness

H6 (hardy – very cold winter)

Herbal Uses

Immunity, Liver, Skin

Flower Colour(s)

Yellow

General Uses

Medicinal, Natural Dye

Make Your Own

Poultice & Plasters, Tincture

Herbal Tradition

Chinese (TCM), Western

Stratification Needed?

Stratification not required

Herbal Teas

Decoctions, Less Tasty Infusions

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Additional information

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