The sweet pea (Lathyrus odoratus) is famous for its delicate blossoms and intense fragrance, making it a favorite in cottage gardens. These vines climb using small tendrils and produce flowers in a wide array of colors from spring until the heat of summer. Whether these flowers return each year depends on the specific type of sweet pea and the climate. Generally, the most common, highly scented varieties are cultivated as annuals, completing their entire life cycle within a single growing season.
Why Common Sweet Peas Are Annuals
The vast majority of sweet peas planted are Lathyrus odoratus, a species that functions as an annual plant. This means the plant must complete its cycle—germination, growth, flowering, and seed production—before it dies completely. The original plant will not survive the winter and cannot regrow from its roots the following spring.
These plants thrive in cool, mild conditions, which is why they are often sown in early spring or late autumn in milder climates. They are genetically programmed to flower profusely and quickly produce viable seeds before the onset of extreme weather. Their short lifespan is due to intolerance for prolonged exposure to excessive summer heat or humidity, which causes the plant to stop blooming and decline rapidly. Furthermore, the root system of the annual sweet pea is not built to store the energy reserves necessary to survive a dormant period, unlike the storage structures found in perennial plants.
Identifying the Perennial Sweet Pea
Lathyrus latifolius is the plant that returns year after year and is often called the Everlasting Pea. This variety is a true perennial vine, surviving colder temperatures by relying on its robust, long-lived root system. Unlike its annual counterpart, the Everlasting Pea is exceptionally hardy and can spread slowly through the garden by means of its rhizomatous roots.
A distinguishing feature of the perennial sweet pea is its lack of the fragrance that makes Lathyrus odoratus so popular. While the flowers are showy and attractive, often appearing in shades of magenta, pink, or white, they carry little to no scent. This perennial species is a vigorous climber that requires a sturdy support structure and can reach heights of six to nine feet. Gardeners who desire a reliable, climbing flower that requires little re-planting effort often choose this perennial species.
How Sweet Peas Seem to Reappear
The common confusion about sweet peas returning often stems from self-seeding. Gardeners may believe the original plant has come back when, in reality, a new generation of seedlings has sprouted in the same location. This process begins when the annual sweet pea stops flowering and its seed pods mature and dry out.
The dried pods eventually burst open, scattering seeds onto the surrounding soil. These seeds have a naturally hard outer shell, which helps them survive mild winter conditions while lying dormant in the ground. When spring arrives and the soil temperature and moisture levels are favorable, these seeds naturally germinate. This new growth of seedlings gives the appearance that the original annual sweet pea has returned.