Originally published on Herbal Medicine from Your Garden
Woad, Isatis tinctoria (syn. Isatis canescens or I. indigotica), is also sometimes called asp of Jerusalem, dyer’s woad or Marlahan mustard. In China, the plant is extensively used for medicine, and each part has a different name: the leaves are called da qing ye, the roots ban lang gen and the pigment qing dai.
You may also occasionally come across the name glastum, which was one of the names used by the ancient Romans. Glastonbury is in an area once known for its woad.
At the time of the Roman invasion, Britons used woad to tattoo blue patterns on themselves, which made them appear fearsome in battle (which is why the Romans called them Picti, which means “painted men”). It can also be used to make a blue dye using alum and potash as mordant. The woad dye-production industry continued in Europe from at least the 10th century until the beginning of the 20th century when synthetic dyes became available.
Woad is a class A noxious weed in parts of the USA. It is a biennial or short lived perennial with a taproot which makes it difficult to eradicate. A native of Central and Southern Europe, it is naturalized in many parts of the UK and across much of the USA. It prefers rich neutral to alkaline (even very alkaline) soil which is well drained, and will not grow in full shade. As the plant depletes the soil, it needs to be planted in a new place every couple of years to maintain a good supply. It’s a member of the cabbage family (which is susceptible to clubroot), so should not be preceded or followed by other members of the same family.
Harvest in the summer, preferably before it flowers to avoid self-sowing, and dry in a cool airy place out of the sun before storing in an airtight colored container. If you wish to use the pigment, this can be extracted from fresh leaves following the instructions given here.
To make a decoction use 30g (1 ounce) of chopped root to 600ml (2.5 US cup, 1 UK pint) of cold water. Bring to a boil, turn down and simmer until the liquid is reduced by half, then strain off the herb and discard. Dosage in either case is up to 1 cup, split into 3 doses.
The leaves have antibacterial, anticancer and antiviral properties, the root is antibacterial and anticancer. Use a standard infusion of leaves to treat viruses and bacterial infections including encephalitis, erysipelas, heat rash, influenza, meningitis and mumps. Use a root decoction to treat fevers, respiratory inflammation in influenza and meningitis, acute infectious diseases including diptheria, dysentery, food poisoning (E.coli and salmonella), streptococcus, typhoid and paratyphoid. The pigment can be used externally as a plaster for inflammation and to staunch bleeding.
Those Picts must have been healthy!
As with all herbs used in remedies, you should grow woad organically to ensure that its active constituents are not masked or etirely eliminated by the presence of foreign chemicals. To find out more about growing organic woad visit the Gardenzone.