(Dyer’s Knotweed, Ko-sen-bon, Liao lan) This is the pink-flowered type. Frost-tender annual to 3 feet tall, a much-branched plant native to Eastern Europe and Asia, including especially Japan and Korea. Traditional use: Fresh and Dried leaves used in treating infections, as a disinfectant, also as a treatment for canker sores and seafood poisoning. Source of indicin–pure indigo dye. I just wanted to point out that the fresh leaves are colored green, not indigo blue. The one picture in the gallery of a blue leaf is how they appear when they wither, with the indigo showing through. Plant does well in standard garden culture, in sun to part shade, with a moderately rich soil and reasonably frequent watering. That said, it is an easily-grown and forgiving plant. Seed is kept refrigerated and should be planted as soon as possible after receipt. Sow 1/4 inch deep in rich soil, tamp securely, keep evenly moist and maintain at 70 to 75 degrees F for best germination. The basic horticultural technique for growing these in the temperate zone is to sow the seed in March, transplant seedlings to field in May, first harvest July, second harvest August.
**Pictures and description from the Strictly Medicinals website**