Ornamental · Fabaceae
Sweet Pea
Lathyrus odoratus
Sown early and cut often, sweet pea repays the effort with scent and color all spring.
Full sun
Every 2–4 days
39–64°F · 4–18°C
50–75 days
Overview
Few garden flowers match the fragrance of Lathyrus odoratus. A fast-climbing annual in the pea family, it ascends by tendrils that seize any support and drape it in ruffled bloom. That scent is the defining trait, and it explains why the species has been grown for cut flowers for well over a century.
Its biology is that of a cool-season plant. Growth begins in the cold weeks of early spring, flowering runs from May into July, and the plant declines as heat sets in. That brief but generous flowering is the direct trade-off for its color and perfume, which is why early sowing so strongly favors the crop.
Sweet pea repays preparation at sowing and consistency thereafter. Scarify and soak the hard seed, maintain even soil moisture, and harvest continuously to sustain flower production. Left uncut, the plant sets seed and stops, so in practice the more you cut, the longer it blooms.
Care
The short version: full sun, rich and evenly moist soil held slightly alkaline, cool growing temperatures, and continual cutting to keep the plant in flower.
Light
Sweet pea flowers most heavily in full sun, tolerating some afternoon shade where spring warms early. Because flowering is driven by light captured during cool weather, greater sun exposure translates directly into greater bloom.
Water
Hold the soil evenly and consistently moist, roughly every 2 to 4 days, and never allow it to dry while the plant is in flower, since moisture stress checks bloom. Water at the base rather than overhead, and ensure the soil drains freely so the roots are not left saturated.
Soil
Provide rich, humus-heavy soil that retains moisture yet drains, amended with generous organic matter to feed the crop and buffer moisture. The species favors a slightly alkaline reaction, a pH of 7.0 to 7.5.
Temperature
As a cool-season species, it grows best between 39°F and 64°F (4°C to 18°C). Both vegetative growth and flowering slow as temperatures rise, which is the physiological reason an early start is decisive.
Humidity
Average outdoor humidity is adequate, so no target figure applies. Air circulation is the operative factor, because crowded, humid conditions favor the powdery mildew and leaf diseases that attack the foliage.
Feeding
Apply a balanced fertilizer about monthly through the growing season. Regular feeding sustains vigor and supports the continuous flower production the plant is capable of.
Pruning
Deadhead spent flowers and cut blooms continually, because seed set signals the plant to stop; removing developing seed keeps it in the reproductive push that produces flowers. Once heat forces decline, remove the whole plant.
Size & spacing
Climbing forms reach 3 to 8 feet (91 to 244 cm) and require a trellis or netting for the tendrils to grip. Allow each plant roughly 2 to 3 feet (61 to 91 cm) of spread, which also provides the air movement that limits foliar disease.
When to plant
Sweet pea is adapted to cool conditions and performs poorly in heat, so timing follows its physiology. Start seed indoors 6 to 8 weeks before the last frost, or sow directly as soon as the soil can be worked, and expect bloom from late spring until rising summer temperatures end it. Where winters are mild, a fall sowing shifts flowering into winter and spring.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: About 6 to 8 weeks before the last spring frost date; in warm-winter areas seed may be sown in fall or late fall for winter and spring bloom
- Plant: As soon as the soil can be worked in early spring; these are cool-season plants
- Harvest: May to July (spring through early summer; declines in summer heat)
Hardiness
USDA hardiness zones: 2–11
Temperature: down to -46°C
Troubleshooting
Most sweet pea problems reduce to two categories: the natural close of a cool-season crop, and a short list of familiar pests and foliar diseases. Distinguish ordinary heat-driven decline from an active problem, then match the symptom below and respond while intervention still helps.
Flowering ceases and the plant collapses as temperatures rise
Because sweet pea is a cool-season annual, a yellowing, failing plant in early summer marks the end of its cycle rather than disease. Once heat and humidity establish, flowering stops permanently. Remove the spent plants, and in warm regions resow in fall to shift bloom into winter and spring.
Fix:
- Treat as a cool-season annual and enjoy spring bloom
- Remove plants from the garden once they decline
- Sow earlier or, in warm regions, sow in fall for winter/spring bloom
Ragged feeding damage on young shoots with slime trails nearby
Slugs and snails feed on tender seedlings, tearing the foliage and leaving glistening trails, with damage heaviest in damp weather that suits their activity. Hand-collect them at dusk when they emerge. Removing leaf litter and other moist refuges, and ringing young plants with a barrier or trap, cuts the population at its source.
Fix:
- Handpick slugs and snails in the evening
- Reduce moist hiding spots and use barriers or traps around young plants
Distorted new growth with insect colonies and a powdery leaf coating
Two issues commonly coincide. Aphids and mites colonize the soft new growth and distort it as they feed, while powdery mildew, leaf spot, or rust develop on foliage held crowded and damp. Dislodge the aphids with a water spray, thin the planting to restore air movement, and keep water off the leaves to deny the diseases the humidity they require.
Fix:
- Wash off aphids with water or treat as needed
- Improve air circulation and avoid overhead watering to reduce foliar disease
Toxicity
The common name misleads: sweet pea is an ornamental, not a food. Its seeds and pods contain a neurotoxic amino acid that produces lathyrism, a disorder of weakness with lasting neurological and skeletal damage, in people, horses, and livestock that consume enough, and gastrointestinal upset in cats and dogs. Keep the pods away from children, pets, and grazing animals.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
A small amount of chewed leaf or stem can produce drooling, vomiting, and gastrointestinal upset. The significant hazard lies in the seeds and pods, where a larger or repeated dose can produce weakness and an unsteady, off-balance gait.
Dogs Mild
Ingested foliage typically causes vomiting and digestive upset. Dogs that break open and swallow the pods or seeds are the ones exposed to weakness and the neurological signs of lathyrism.
Horses Toxic
Horses are severely affected. Ingestion produces weakness, lethargy, restless pacing, head pressing, tremors, and seizures, and severe cases can be fatal.
Rabbits Toxic
The neurotoxic amino acids concentrated in the seeds and pods render the plant unsafe for rabbits, so it should be kept out of reach rather than offered as any part of their forage.
Livestock Toxic
Cattle, sheep, and goats that graze the seeds over time develop lathyrism, with muscle weakness and permanent skeletal and neurological damage. They should be fenced off from the plants entirely.
Birds Toxic
The poisonous seeds and pods make sweet pea unsuitable around poultry and pet birds, which readily take seed. The seed pods should be kept beyond their reach.
People Caution
No part of the plant is food, notwithstanding the name. The pods and seeds are poisonous, and prolonged consumption of the seeds can cause lathyrism, with weakness and neurological and skeletal damage, so children should be kept away from the seed pods.
Keep seeds and pods away from pets and children; do not confuse the ornamental sweet pea with edible garden peas. The pods are inedible and poisonous.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
Sweet pea cultivars fall into groups selected for different ends, some for flower size and stem length, others for fragrance alone. These are the groups worth recognizing.
Spencer types
The standard exhibition and cut-flower group, distinguished by large, frilled and ruffled blooms borne on long stems.
Old-fashioned / Grandiflora types
Smaller in the flower but the most powerfully and sweetly scented, carrying the fragrance for which the species was named.
Cupani / Matucana
An heirloom bicolor close to the wild type, bearing deep maroon and violet flowers with an intense fragrance.
Dwarf / bush types
Compact, mounding plants requiring little or no support, which adapts them to containers and edging.
How to propagate
Sweet pea is propagated by seed, and the single obstacle is a hard, water-resistant seed coat that must be breached before germination will proceed.
SeedModerate
Sow indoors 6 to 8 weeks before last frost, or direct sow in early spring as soon as soil can be worked; in mild climates sow in fall. · Germinates in roughly 1 to 3 weeks; flowering begins about 50 to 75 days after sowing.
Sweet pea is raised from seed, and the hard seed coat is the one obstacle to germination. Scarify each seed by nicking or filing it and soak it in warm water for about 24 hours before sowing to admit moisture and speed the process. Start indoors 6 to 8 weeks before the last frost, or sow directly in early spring once the soil can be worked, sowing in fall in mild-winter regions. Germination follows in roughly 1 to 3 weeks, and the first flowers open about 50 to 75 days after sowing.
Myths
Sweet pea seeds and pods are edible like garden peas.
The ornamental sweet pea is a different species from the edible garden pea, despite the close resemblance of the pods. Its seeds and pods are poisonous, and sustained ingestion of the seeds can cause lathyrism, a serious neurological and skeletal disorder. It is a crop for the flower, never for the table.
Sweet peas flower continuously through summer.
It is a cool-season annual whose flowering spans spring into early summer. As heat and humidity arrive the plant declines rapidly and generally warrants removal, so the display is a spring event rather than a summer-long one.