also called: Persicaria tinctoria
Indoors 6-8 weeks before fear of frost, start your seeds. When they are tiny but sturdy, thin and spread out into containers, or directly into your garden. Keep the ground moist, and keep your leaves wet to keep from drying out. Indigo likes it hot and humid, so don't let the soil get dried out!
When plants become 1-2 feet tall and a crushed leaf turns navy blue, you can harvest your plants. Cut the stems several nodes up from the ground (it will re-sprout at those nodes). You may be able to harvest the re-growth several times. Harvest and make up your dye vat on the same day. Dried leaves won't always dye well or at all.