Can you clarify your picture please- where is the verbena you're referring to (can't tell even under magnification) and are you talking about verbena bonariensis?

Yes Bamboo it is Bonariensis and I don't blame you I can barley make out the tiny bit of flowering and it's only on the extended stem the other upright ones are dead, thanks

It looks like it is getting too much shade, to me, but V. bonariensis is always a bit transparent. If you see "drifts" of Verbena, it is almost always the annual Florist's Verbena (V. hybrida), grown as a summer bedding plant. I would plant V. bonariensis in small groups at strategic locations in a cottage or "wild" garden, and be ready to manage the volunteers next spring.

Yes, struggling for light and space. I find that I do best with them if I pot up the self seeds and pinch the growing tips out and they become a bushier plant before replanting.

I think the major problem is its situation too - its hard up against a wall for one thing, and they do better a foot or so away from a wall or fence behind. I always plant plenty of these in between things in sunny areas, and yes, grouped together, they do form a drift of flowers, but in their second year, you do need to cut them right down as growth begins, along with any new self set seedling plants, otherwise you just get one straight stem with a flower or three at the top.

Many thanks for all your replies and Bamboo has it right as I've never cut it back so will in future.

Second year they make drifts? That explains my experience: they rarely survive the summer here.

Well, once the plant gets large (2nd or 3rd year if it gets that far) with a rootball maybe 7 inches across, and several stems, then yes, you get the 'drift' effect. But, in Charnwood's case, it doesn't look like there's sufficient room for the plant to develop any real size at the root. If I want a solid, drift effect quickly, I'll plant 3 or 5 in one area, but more usually, I just plant them in between shrubs so they appear well above the surrounding planting, and just give that height and make an airy, light flowery addition to the bed or border.