Vervain produces dense clusters of many small flowers, in a wide range of colours, and is valued for its long flowering season. It is also very attractive to butterflies. Some varieties self-seed freely.
There are about 250 annual and perennial species, originating from the tropical and sub-tropical regions of America.
They require full sun and well-drained soil to thrive. Some varieties are fully hardy, while others may require some protection to survive in harsh climates.