Start seeds inside 3/15-4/1 at 70 to 75°. Sow seeds 1/4" deep. Days to seed germination: 10-21 days. Transplant outside after last frost (late May). Space plants 12" apart. Plant in full sun in a location with lots of compost & organic fertilizer.
Harvest for dye in July & August before the first frost. Harvest by clipping stems just above the lower joints (swollen area) in the stem - this allows them to sprout back for another cutting. Don't cut too low or the plants will not sprout back. Use indigo leaves fresh or dried for dye. Strip leaves from stems.
Japanese Indigo seeds are mature in fall making it difficult to grow seeds in the north. To grow them for seeds, start seed inside in February and, when needed, transplant into a big container and continue to grow plants inside until late May. Then plant large plants outside which will produce seeds earlier. Cover plants in the fall to protect from light frost. Mature seeds are dark in color.
