Hemp agrimony (Eupatorium cannabinum) is one of the very best plants for attracting butterflies: even better than buddleia. Despite its name, it has nothing at all to do with cannabis or hemp.
Hemp agrimony is a hardy perennial that is native to the UK. Although seldom grown as a garden plant, it is certainly worth considering if you are planning a wildlife area in your garden. It prefers soils that are moist a good deal of the time and quite a sunny position. Although it can be grown from seed, it is simpler and more reliable to divide a clump if you know somebody who has some they can share with you.
The flowers, a frothy mass of pale pinky-mauve appear in July and August – just in time for many butterflies. The dried flowers and leaves of hemp agrimony are sometimes used as an infusion which has a mildly cleansing and toning effect.