Dyers woad begins as a rosette with small, long tear drop-shaped leaves that have a white spine in the center. It grows up to three feet tall with many branching stems, bluish-green alternated leaves that have a white spine, and bright yellow flowers that appear late in the season. Dyers woad was originally cultivated as a source of blue dye, and it is allelopathic, which means that it produces chemicals that inhibit growth in other plants close by.