Medieval herb garden blog 72: Woad

There is still a very large section of woad up by the gatehouse. It was planted for use in natural dyeing workshops.

Carole then filled up the sales barrow again. We now have some white sage and verbena bonariensis on sale.

At about 12:30pm, after talking to some more visitors, we decided that the heat had beaten us and “called it a day”.

During its first year, the plant grows a dense, low-lying cluster of lance-shaped-to-oblong leaves. These leaves are soft, hairless and bluish-green. They with smooth or slightly toothed edges. The leaves are 6 to 12 inches (15 to 30 cm) long and 2 to 6 inches (5 to 15 cm) wide. The leaves have a prominent pale whitish midvein that runs down the centre of the leaf on the upper surface. This makes the plant easy to spot and remove if required.

In its second year, the plant produces tall, flowering stalks. The foliage changes. The leaves become narrower, smaller, and are arrow-shaped. They alternate up the main flowering stems. It grows up to a height of 5 ft (1.5 m) and a width of 3ft (90 cm).

Woad flowers during late spring and early summer in its second year. The bright 'neon yellow' flowers are tiny and have four petals. They grow in large, branched sprays. The flowers have a mild, sweet smell. When the foliage is bruised or crushed, it releases a sharp, peppery, and cabbage-like smell. This is due to its glucosinolate content.

Although woad is a member of the Brassicaceae (mustard / cabbage) family, its leaves are very bitter. In Sicily and Italy, the boiled flower buds are sometimes eaten in salads and omelettes. The flower buds can also be pickled.

Woad is known for its use in the production of an indigo dye. After chopping and multiple fermentations, the precursor chemical indican turns into the intermediate chemical indoxyl. When this is exposed to oxygen, it turns into the recognisable blue pigment indigotin.

Woad also contains the chemical indirubin. This is a reddish pigment which can add a red tinge to the final blue dye.

An Irish law from the 700s AD stipulated that how woad should be shared by a divorcing couple. It was to be shared based on which step of the fermentation process it was in. The wife could claim "a third of woad steeping in vats, half, if it is caked"

The illustrator of the Lindisfarne Gospels (c. 720 AD) used a woad-based pigment for blue paint.

The use of woad is described in a late 1200s North Italian manual on book illumination ('Liber colorum secundum magistrum Bernardum').

In Germany, there have been attempts to use woad to protect wood against decay.

Woad is listed as a noxious weed by the agriculture departments of 11 states in the western USA.

Both the large white (pieris brassicae) and small white (pieris rapae) caterpillars are common pests that feed on woad leaves. Flea beetles (phyllotreta spp) also eat it.

The root-mining weevils (aulacobaris licens) and aulacobaris fallax lay eggs in the petioles or roots. The larvae feed inside the root crown. Seed-feeding weevils (bruchela exigua) and ceutorhynchus peyerimhoffi are known to develop within woad seeds.

Woad's bright, yellow flowers are attractive to honey bees, native bees, and hoverflies (syrphid flies). They feed on the nectar.

Braconid wasps are often found on woad. They act as biological control agents by parasitising caterpillars and aphids.

Woad was used for its high antiviral, antibacterial and anti-inflammatory properties.

It was traditionally used to help soothe sore throats, wounds and ulcers. It could reduce 'toxic heat' and support immune response during respiratory infections.

Woad was a cure for St Anthony’s Fire. It “stays defluxion of the blood to any part of the body”.

*As always, this isn't to be considered medical advice today. Please don't use any plants mentioned in these blogs as medicine without advice from a doctor.