Verbena bonariensis (Purple top)
Verbena bonariensis is an herbaceous perennial, with clusters of small, purple flowers from summer to autumn held on tall stems. Leaves are narrow and sparse. Good for adding height and cloud of colour at the back of your borders.
Grow in moist, well-drained, moderately fertile soil in full sun. Protect with a dry winter mulch in areas with cold winters. Self seeds and spreads, but can be easily controlled in your garden.