The question of whether sweet peas are annuals or perennials is often confusing because the term refers to different species within the genus Lathyrus. Sweet peas are climbing flowering plants, prized for their delicate, butterfly-like blooms and intense fragrance. While the most commonly grown and highly scented variety is a true annual, a related plant with a similar appearance is a long-lived perennial. The specific species determines the plant’s lifespan.
Clarifying the Confusion: The Two Types of Sweet Peas
The plant most people recognize is the annual species, Lathyrus odoratus, cultivated widely for its delightful scent and broad range of colors. This species is a true annual, meaning it completes its entire lifecycle—from seed germination to flowering and seed production—within a single growing season before dying off. The highly popular, fragrant cultivars, such as the Spencer types, all fall under this classification and must be replanted every year.
In contrast, the perennial sweet pea, Lathyrus latifolius, is a long-lived herbaceous plant that returns each spring from its rootstock. This type is often called the everlasting pea because it can survive for many years, commonly growing wild along roadsides or in established gardens. A significant botanical difference is that while L. odoratus is intensely fragrant, L. latifolius flowers are generally unscented, making the perennial type less popular with those seeking the classic sweet pea perfume. The perennial varieties also offer a more limited color palette compared to the many hues available in the annual species.
Lifecycle Impact on Sowing and Seasonality
The fundamental difference between the annual and perennial lifecycles dictates the necessary planting strategy for each plant. Since Lathyrus odoratus has only one season to flower and set seed, the timing of sowing is adjusted to maximize this short window. Gardeners often start annual sweet pea seeds indoors in late winter or sow them directly outdoors in the autumn in milder climates. This early start allows the plant to develop a robust root system during the cool season, preparing it for the burst of growth and bloom in the late spring and summer.
The goal with the annual type is to achieve flowering before the summer heat causes the plant to stop blooming and quickly produce seeds, which signals the end of its life. Because they do not survive winter in most regions, annual sweet peas must be sown again every year to ensure a continuous display. Conversely, the perennial Lathyrus latifolius is a more permanent fixture in the garden, requiring an initial establishment phase but no annual replanting. The perennial type is frost-hardy and will die back completely to the ground in the fall, only to emerge from its roots the following spring, offering a reliable return year after year.
Extending the Bloom Season
For the annual sweet pea, maintenance focuses on actively delaying the plant’s natural impulse to complete its single-season lifecycle. The primary technique used to extend the flowering period is deadheading, which involves removing spent or fading flowers. This action prevents the plant from using its energy to develop seed pods, which is the biological signal for L. odoratus to cease flower production. By consistently removing the spent blooms, the gardener encourages the plant to continue producing new flowers in an attempt to successfully reproduce.
A clean cut with sharp snips should be made just above a leaf node below the spent bloom to encourage new growth. This process needs to be done frequently, sometimes daily during peak bloom, to prevent any seed pods from forming on the vine. The vigorous climbing habit of annual sweet peas, which can reach heights of four to eight feet in a single season, necessitates strong structural support. Providing a trellis or netting ensures the plant climbs efficiently, allowing it to put maximum energy into producing fragrant flowers.