Plants may need support ... Upright stems carry small, grey-blue, thistle-like flowers that sit on a broad, spiny ruff that adds enormously to their impact. ‘Picos Amethyst’ (15-18in) has ...

Like many other biennial invasives, bull thistle is able to produce a large seed bank that can remain viable for up to 10 years! As a result, the plant can easily spread and form dense stands in ...