Lemon Verbena is growing well out in the field, here in North Texas. The majority of commercial Lemon Verbena is grown in Central America, South America and in various countries in the Middle East. In other words, once established, the growing plants flourish in hot weather.
Here's a photo of the same harvest, after drying on indoor racks, with a fan moving air across them for good circulation. The leaves are crisp-dry for storage in only one day, this time of year, and they are stored in a brown paper grocery bag for continued air circulation.
In contrast, our mint and basil take two or three days to dry in the same location, temperature and humidity.