Verbena bonariensis with its tall, narrow, sparsely-leafed stems on top of which flattened heads of bright lavender-purple flowers appear in late-summer can grow to 6 ft (180 cm) tall and can spread to 3 ft (90 cm) wide. This is Verbena ‘Lollipop’ which is a dwarf cultivar and grows at half the height, although mine is much closer to 6 ft! Possibly because I didn’t cut it back.
Its nectar-rich flowers help sustain bees and butterflies well into autumn. To make it bushy cut back the stems in spring to about 6 inches above the ground and lightly prune the tips of the plant throughout summer.
These white-tailed bumblebees were having a feast.
Cornwall in Colours 
That’s a useful tip about cutting them back – thank you
The bees are little acrobats, aren’t they? Lovely shots.
I have V. Lollipop too, and they’re also growing taller than I want. I didn’t know about cutting them back – that will be put right next spring. I also have a number of V. Rigida which I grew from seed this year, I expect that tip could apply to them as well.
Your photos are superb – not an easy plant to photograph!
oh how wonderful