Tender annual related to the knotweeds, with broad oval leaves and small pink flower spikes in late summer. The principal indigo dye plant of East Asia and a reliable cold-climate alternative to tropical Indigofera.
Hardiness ratings
| System | Rating | Temperature range | How to read it |
|---|---|---|---|
| USDA hardiness zone | Zone 4–11 | −34.4 °C to 10 °C | Zones where it can be grown as an annual — not a frost-tolerance rating |
| RHS hardiness rating | H4 | −10 °C to −5 °C | Plant needs at least this level of cold tolerance |
| Canadian plant hardiness zone | Zone 4–9 | −29 °C and warmer | Zones where it can be grown as an annual — not a frost-tolerance rating |
| Australian (ANBG) zone | Zone 1–7 | −15 °C and warmer | Zones where it can be grown as an annual — not a frost-tolerance rating |
As a tender annual, Japanese indigo doesn't overwinter — the zone range shows where the growing season supports it. See the RHS rating for its actual cold tolerance.
Growing notes
- Blue indigo dye extracted from fresh leaves by direct vat fermentation (the Japanese aizome tradition) or by drying for storage and later fermenting
- Distinct from the tropical Indigofera tinctoria (already in the database) — Japanese indigo is cold-tolerant and grown as a temperate annual, Indigofera demands tropical heat
- Cut-and-come-again — flush the plant with water and cut twice in a season for double yield
- Self-seeds in warm climates — strictly annual where frost occurs
Categories
Related plants
Cross-check Japanese indigo against your zones