Gentiana Asclepiadea is also called Willow Gentian, Milkweed Gentian grows to about 1 meters tall and it produces blue trumpet shaped flowers in late summer early fall. It is a herbaceous perennial and it can add a nice touch of extraordinary blue color to your borders. It is native to Europe and is part of the Gentianaceae family of plants. Propagate by seeds or dividing clumps after flowering. It is usually pest free.