Japanese indigo

6. Japanese indigo Persicaria tinctoria (formerly Polygonum tinctorium)

Other names: dyer’s knotweed

Traditional source of indigo blue dye in Japan and southeast Asia.

Easier to grow in temperate climates than Indigofera, produces more indican than Woad.

Dye: the same complex extraction and fixing process as Woad produces shades of blue.