Bighead Knapweed, Centaurea macrocephala, is one of the most asked-about plants at the Jensen-Olson Arboretum when it’s in bloom. It usually blooms in late July/early August, but this year it is well ahead of schedule with our sustained warm weather. While many knapweeds are listed as highly invasive, C. macrocephala is well-mannered in gardens here in Southeast Alaska. In Washington and in Alberta, Canada, however, it is listed as a noxious weed. This large perennial grows to almost five feet tall with bright, chrome-yellow flowers up to four inches across.