Lathyrus odoratus Seeds | Sweet Pea
LATIN NAME: Lathyrus odoratus
COMMON NAME: Sweet Pea
Plant Profile
Lathyrus odoratus is a diploid with a compact genome of fourteen chromosomes, which has made the genus a long-running subject in legume genetics. The plant climbs with tendrils at the tip of each pinnate leaf and anchors itself with a deep taproot, so it resents transplanting from open trays. On its native limestone it survives dry summers as seed, popping up wherever disturbance opens the scrub, and it is precisely that strategy, seed as the lifeboat, that makes fresh seed so reliable in the garden.
Through the 1880s and 1890s Henry Eckford of Wem crossed and selected the wild Sicilian into the Grandiflora race, larger flowers on longer stems in a widening colour range, and made sweet peas a Victorian sensation. Then in 1901 Silas Cole, gardener to the Earl of Spencer at Althorp, noticed a single frilled sport in a row of Eckford’s stock; he fixed it and named it ‘Countess Spencer’, and the large, wavy-petalled Spencer race swept the exhibition benches and remains the dominant type in commerce.
Sweet peas are cut-flower aristocrats when handled right. Pick stems with two or three flowers just opening, in the cool of morning, and stand them at once in deep, cool water; some growers add a pinch of sugar. Held in a cool room they keep for several days, and regular picking is the real secret of the crop, because every pod that begins to swell tells the plant its season is over.
Science & Biotechnology
Sweet pea perfume has been analysed as a complex blend of volatile compounds in which phenylpropanoid and terpenoid molecules dominate, and breeders have learned that selecting for giant ruffled blooms can quietly breed the scent out. Modern scented strains are marketed on that chemistry: sniff before you buy, because a frilled exhibition flower with no fragrance is a common disappointment.
The seeds contain beta-aminopropionitrile and related compounds, and eating quantities of Lathyrus seed is genuinely dangerous; a related species, the grass pea, causes the paralytic disease lathyrism where it forms a famine staple. Sweet pea seed causes the related osteolathyrism in feeding trials, so the garden rule is absolute: the flowers are for the vase and as garnish in moderation, the seeds are not for eating at all, and keep them away from poultry and children.
Uses & Benefits
The flower is built to the classic papilionaceous plan: a broad upper banner, two side wings, and a keel that hides the reproductive parts, and it is the keel that tells you about pollination. Only heavy-bodied bees can lever the keel open to reach the nectar, dusting themselves with pollen as the sexual column springs up. Wild-type flowers carry the powerful orange-blossom-and-honey scent that gave the species its name, odoratus, and the scent strengthens in warm, still air at the end of the day.
Growing from Seed
The seed coat is hard and water-tight, so chip it lightly with a knife or soak it briefly before sowing into deep pots or root trainers filled with a free-draining loamy mix. Sow two seeds to a pot, a knuckle deep, and grow them cool and bright; leggy, warm-raised plants never catch up. Slide the whole rootball out and plant it without disturbing the taproot once the soil is workable and the risk of hard frost has passed.
Give the plants a stout support net or bean sticks, tie in the first leaders, and pinch out the tips after the second leaf pair to promote side shoots. Feed with a balanced fertiliser until bloom, then switch to a high-potash feed, and water deeply in dry spells, as drought invites the mildew. Pick twice each week at the height of the season and the row will bloom until the heat closes it down.
Our Take
Grow sweet peas for the scent first and the colour second, and never let a pod set. If you like leguminous climbers with a story, the vegetable side of the family is close by: Oregon Sugar Pod pea for the kitchen, cowpea seed for hot summers, pigeon pea seed for warm-climate hedges, and chickpea seed for a drought-hardy cousin. Chip, soak, and sow deep, and ‘Cupani’ will repay you with the original perfume of Palermo.
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