The sweet pea is a highly popular ornamental flowering plant, cherished globally for its intense fragrance and the wide spectrum of colors it brings to gardens. This beloved flower is botanically distinct from the common edible pea, making a clear understanding of its identity and cultivation necessary for anyone wishing to grow it safely and successfully.
Botanical Identity and Origin
The sweet pea belongs to the genus Lathyrus and is scientifically designated as Lathyrus odoratus. This species is classified within the Fabaceae, or legume, family, which also includes various beans and true peas. The Latin term odoratus translates directly to “fragrant,” reflecting the plant’s most prized attribute.
The sweet pea is native to the Mediterranean region, specifically originating in southern Italy, Sicily, and the surrounding Aegean Islands. It was first documented as a wild species in the late 17th century by a Sicilian monk and botanist, Francesco Cupani. Following its introduction to Britain in 1699, breeders quickly developed the diverse cultivars seen today.
Distinctive Physical Features
The sweet pea is an annual climbing plant, typically reaching heights of six to eight feet when provided with support. It uses specialized, branched tendrils to twine around trellises, netting, or other structures. Without this support, the plant will grow into a significantly shorter, bushy mound.
The flowers are instantly recognizable due to their papilionaceous, or “butterfly-shaped,” structure. This shape is composed of one large, upright petal (the standard or banner), two side petals (wings), and two lower petals fused into a boat-like structure (the keel). Cultivated varieties offer a broad palette of colors, including pink, red, blue, purple, and white, though a true yellow color has remained elusive. The powerful, sweet fragrance is the plant’s signature characteristic.
Essential Growing Requirements
Sweet peas are best grown as a cool-weather annual, meaning they prefer to establish their root systems and flower before the intense heat of summer arrives. In regions with mild winters, seeds can be sown in late autumn for early spring blooms. Gardeners in colder climates should sow seeds indoors four to six weeks before the last expected frost, or direct-sow into the garden as soon as the soil is workable.
The ideal location provides full sun, though partial shade is tolerated, particularly in southern regions where afternoon shade helps keep them cool. Sweet peas are heavy feeders and require rich, deep, well-draining soil with a neutral pH between 6.0 and 7.0. Incorporating compost or well-rotted manure prior to planting provides the necessary nutrients for robust growth.
The vining nature necessitates a strong support structure, such as a trellis, wire mesh, or netting, to prevent sprawling. Consistent moisture is necessary, as the plants will not thrive if allowed to dry out during warm weather. To encourage a bushier plant and increase blooms, the central growing tip of the young seedling can be pinched off once it reaches about six inches. Removing spent flowers (deadheading) or harvesting frequently prevents the plant from setting seed and prolongs the flowering season.
The Critical Safety Distinction
The sweet pea (Lathyrus odoratus) is purely ornamental and is considered toxic if ingested, making a clear distinction from the edible garden pea (Pisum sativum) necessary for safety. The seeds, pods, and vegetative parts contain neurotoxins known as lathyrogens, which are amino acid derivatives. The most significant of these compounds is beta-aminopropionitrile.
Ingesting large quantities of the seeds over a prolonged period can lead to lathyrism, a paralytic syndrome which affects the central nervous system and connective tissues. Symptoms in humans and animals can include muscle weakness, difficulty walking, slow pulse, and in severe cases, paralysis or convulsions. Due to this toxicity, sweet peas should be kept out of reach of small children and pets, and the seeds must never be consumed.