I would say 'yes' - give them a careful trim. I have been deadheading mine. They don't need a trim yet.
Cutting Back in the Spring

Cut back the tips of the stems of your purple verbena in the spring to encourage branching. You'll have stockier, bushier plants with more blooms as a result. Water the plant thoroughly and apply fertilizer to further encourage growth and blooms.

Cutting Back to Stimulate Blooming

Cut back purple verbena if blooming wanes in midsummer. Trim a quarter of the height and width of the plant using grass cutters or scissors. Then, water the purple verbena thoroughly, and apply liquid fertilizer diluted to half the strength recommended by the manufacturer for standard use.

Here is a link that might be useful: Do You Cut Back Purple Verbena?