From a botanical perspective, the common sweet pea (Lathyrus odoratus) is classified as an annual plant. Its fundamental, genetically programmed life cycle is to germinate, grow, flower, set seed, and die within a single growing season. The plant's entire biological purpose is to reproduce once and expend all its energy into creating the next generation. After flowering and seed production, the plant's systems begin to senesce; its vascular tissues are not designed to transport nutrients and survive freezing temperatures or extended periods of dormancy. It has not evolved the necessary structures, such as a robust perennial crown or hardy rootstock, to persist for multiple years.
It is crucial to distinguish Lathyrus odoratus from its perennial relative, Lathyrus latifolius. This species, known as the everlasting or perennial pea, is a true perennial from a plant's point of view. It develops a deep, hardy root system and a woody crown that allows it to survive winter dormancy and resprout the following spring. Its biological strategy is different: it invests energy in establishing a permanent structure before focusing on reproduction in subsequent years. However, it is important to note that Lathyrus latifolius, while perennial, is not fragrant and is often considered more vigorous and less refined than its annual cousin.
A plant's classification as annual or perennial is often a function of its native climate. Lathyrus odoratus originates from the Mediterranean, a climate with mild, wet winters and hot, dry summers. In this environment, the plant completes its life cycle during the cool, moist season and dies back as the harsh summer arrives. Its biology is not adapted to withstand prolonged freezing. In colder climates (USDA zones 7 and below), winter soil temperatures fatally damage the root system. In warmer climates (zones 8-10), the plant may succumb to the heat of summer rather than the cold of winter. Therefore, the climate acts as the ultimate determinant of whether the plant's annual life cycle is enforced.
While the individual Lathyrus odoratus plant is annual, it can create the illusion of being a perennial through a vigorous self-seeding strategy. If flowers are not deadheaded and are allowed to form and drop seed, new plants will often germinate the following growing season. From the garden's perspective, sweet peas reappear each year. However, from the plant's point of view, these are entirely new genetic individuals, not the original plant regrowing. This is not true perennialism but rather a successful annual reproduction strategy that mimics it, ensuring the species' continued presence in a favorable location.
