Joan Senior produces large, trumpet-shaped flowers, typically 6 inches in diameter. The petals are a creamy, off-white color with a gentle ruffle and recurved shape, while the throat is a striking chartreuse or lime-green. The foliage is slender, arching, and grass-like. It is considered semi-evergreen in milder climates, meaning it may retain some leaves through the winter. In colder regions, the foliage will die back and re-emerge in the spring.