The legendary blue dye plant. Japanese Indigo is the easiest and most reliable way to grow your own indigo pigment at home.
Used for centuries in traditional textile dyeing, this lush, leafy plant is grown not for its flowers, but for the vibrant blue pigment hidden in its green leaves. With proper harvesting and processing, indigo yields one of the most colorfast and striking blues in the natural dye world.
Basic Info:
- Common Names: Japanese Indigo, Dyer’s Knotweed
- Color (for dyeing): Blue
- Flower Type: Small pink-white flowers (not used for dyeing)
- Scientific Name: Persicaria tinctoria (formerly Polygonum tinctorium)
Cultivation Info:
- Days to Maturity: 75–90 days
- USDA Hardiness Zone: Annual in Zones 3–10
- Planting Depth: Surface sow or cover very lightly (needs light to germinate)
- Plant Spacing: 12–18 inches apart
- Growth Habit: Bushy; 2–3 feet tall
- Soil Preference: Moist, well-drained, rich soil with high organic matter
- Light Preference: Full sun
Additional Information:
- Taxonomy: Family Polygonaceae
- Seed Type: Open-pollinated
- Sow Instructions: Start indoors 6–8 weeks before last frost; requires warmth to germinate (70–75°F); transplant out after danger of frost has passed
- Diseases: Rare; watch for root rot in soggy soils
- Pests: Aphids, flea beetles (generally minor)
Natural Dyeing Use:
Indigo from Persicaria tinctoria requires fermentation or extraction to unlock its blue pigment, as it is not water-soluble in plant form. The fresh leaf “salt rub” or ice extraction method can produce soft denim blues without chemicals. For stronger pigment, leaves can be processed into indigo paste or used in traditional fermentation vats. Indigo dyes both protein (wool, silk) and cellulose fibers (cotton, linen) exceptionally well without the need for mordants.
Troubleshooting Tips:
- Slow growth? Indigo is a heavy feeder—use compost-rich soil and water regularly.
- Weak color in leaves? Harvest before flowering and avoid drought stress for best pigment levels.
- Poor germination? Use fresh seed and maintain high humidity and warmth during germination.