In A Garden to Dye For (St. Lynn’s, 2014), Chris McLaughlin teaches you how to make the most of your garden by harvesting different plants to create your own clothing dyes. She walks you through each type of plant, explaining where the color comes from and how best to get it for yourself. In the following excerpt, she goes though the uses of Japanese Indigo.
Japanese Indigo (Persicaria tinctoria or Polygonum tinctorium)
AKA Dyer’s knotweed, Chinese indigo
Japanese indigo is an annual plant that gives pure blues, just like the famous Indigofera, but P. tinctoria is more widely grown. Start seeds about 6 weeks before the last frost and harden them off before planting outdoors. Since Persicaria tinctoria seeds are notoriously short on viability, try to save seeds from this plant every year. Even seeds as young as a couple of years old may not germinate. Japanese indigo likes a well-composted garden bed and full sun to be happy. It also loves its water, so keep its feet moist.
This bushy fellow propagates readily from seed, but just as easily from stem nodes (the little bump on the stem where a leaf grows). This makes it the perfect candidate for taking cuttings for propagation. You could also skip both and just carefully press one of the stems to the ground. Use a rock or wire to keep it pressed against the soil and cover the joint with soil so that new roots will form. Once they’ve taken hold you can cut it from the mother plant.
Harvest leaves from mid-summer to the end of the fall. Dyer’s knotweed grows quickly: 2-3 feet tall if left to its own devices, but you’ll probably harvest them between 1-2 feet tall. The leaves are ready when you pinch (bruise) them and you get a dark blue stain. Count several nodes from the soil level and cut the top of the stem off above those nodes for processing. More leaves will grow in their place and you can harvest again before the season is up.
Using fresh indigo leaves immediately will give you the deepest blues. However, dried leaves can work, too (see the recipe in the section “Blue for You,” below).
Note: despite the similar name, this is not the infamous invasive plant species ‘Japanese knotweed’ (Polygonum cuspidatum). That said, be sure that P. tinctoria is not a problem in your neck of the woods.
Where the Color Is
Just like Levi Strauss, it’s the lovely blue in Japanese indigo’s leaves that we’re going for here (see “Saturated Silk” and “Blue for You” sections).
More from: A Garden to Dye For• DIY Madder Dye
• Pokeberry Dye Recipe
• Homemade Calendula Dye
• DIY Yarrow Yellow Dyes
• DIY Mint Leaf Natural Dye
• Natural DIY Bee Balm Dye
• Dyes from St. John’s Wort
Reprinted with permission from A Garden to Dye For, by Chris McLaughlin and published by St. Lynn’s, 2015.