Lobelia is a perennial plant that is often considered an annual because growing conditions must be perfect for it to survive and flower another year. More than 360 species of lobelia are grown as annuals, perennials or shrubs.
The trailing lobelia (Lobelia erinus) -- also known as "Cambridge Blue" -- is the plant most commonly found growing along the edge of the flower bed. It may be treated as a perennial or an annual plant, depending on the climate of the location in which it is grown. With perfect growing conditions, it will grow year after year. After cold winters it will die after flowering and setting seeds.
The great blue lobelia (Lobelia siphilitica) is considered a perennial herb. It has erect stems, ranges from 60 to 90 cm (2 to 3 feet) in height, and flowers in late summer.
Lobelia inflata is considered a poisonous annual plant. It is said that people once chewed and smoked the leaves of the Lobelia inflata. This type of lobelia can survive in poor soil.