Woad is an interesting plant. The blue dye made from woad is ancient - think Mel Gibson's face in "Braveheart"! Here in Colorado, it's on the noxious plant list A, though it is not common, merely "of concern". It's a mustard (Brassicacae) and I would love to grow it, but try to stay away from the invasives! Also, someone said cosmos was easier to grow than calendula, but I have the opposite experience. Especially sulfur cosmos, which is the dye-producing variety - that one is harder to grow for me than the more common red/white/pink variety. Too bad those don't make dye! Calendula, on the other hand, I grew once and now have it everywhere. A prolific seed setter.
Anyway, very interesting discussion. I'm a knitter but don't spin or dye (yet). Love this group and have been reading it for months, though this is my first post.
