Tall biennial brassica with rosettes of blue-green leaves the first year and clouds of small yellow flowers the second. The pre-Columbian source of blue dye across Europe, displaced commercially by tropical Indigofera in the 17th century.
Hardiness ratings
| System | Rating | Temperature range | How to read it |
|---|---|---|---|
| USDA hardiness zone | Zone 4–9 | −34.4 °C to −1.1 °C | Plant tolerates down to this zone |
| RHS hardiness rating | H6 | −20 °C to −15 °C | Plant needs at least this level of cold tolerance |
| Canadian plant hardiness zone | Zone 4–8 | −29 °C to −1 °C | Plant tolerates down to this zone |
| Australian (ANBG) zone | Zone 1–5 | −15 °C to 10 °C | Plant tolerates down to this zone |
Growing notes
- Blue dye extracted from the first-year leaves by fermenting, drying, balling, then fermenting again to produce the active indigo precursor — a complex multi-step process taking weeks
- Same indigo molecule as the tropical Indigofera tinctoria (already in the database as a nitrogen fixer with dye use) — yield per acre is much lower, but woad is hardy where Indigofera will not grow
- WARNING: Listed INVASIVE in parts of the western United States — biennial seed pods disperse widely on wind, do not plant where it can escape into rangeland
- Self-seeds readily — strictly biennial, must allow two years for the dye crop
Categories
Related plants
Cross-check Woad against your zones