The final, most drastic cutback will be in the fall when plants are cutback so winter annuals such as pansies, dianthus or bluebonnets can the interplanted among the Verbena. The third problem with Verbena is that they are susceptible a few to pests. I mentioned that Verbena is susceptible to the fungus powdery mildew if planted in a wet, shady locale. Organic growers can use insecticidal soaps or sulfur dust but an invasion of spider mites MUST be dealt with or plants can be destroyed. Leaf miners which make little trails in the leaves do not cause significant damage but are ever-present.
Thrips can also be a problem and can be controlled with the same insecticides.
Verbenas have been known since the most ancient times. The druids had the greatest veneration for the plant, and before gathering it offered a sacrifice to the soil. They also held bunches of verbena between their hands during their devotions. When the Romans sent messengers of peace to other nations they adorned their apparel with sprays of verbena. Images of Venus Victrix were often crowned with wreaths of verbena and myrtle.