When to cut back verbena

During the spring tidy-up. This will very much depend on the weather. If you are growing other perennials, you may see some of them starting to make some growth; this is the time to start. I would be inclined to leave the verbena till late in the process as it's not as tough as some things and a late cold spell may cause heartache.

I think you mean Verbena bonariensis, Viper. I agree with Andrew - I have not yet cut mine back, I have been watching them to see when new growth starts from the base. It's just beginning to appear this week on the older plants - the new ones bought/grown last autumn are still green and growing, so I shall just cut out the dead flower stems on those - but not yet!

Thank you for your comments, I agree wi the self seed and last month I had serveral gold finch visiting to feed, 12 was the most i'd counted at one time.