Ornamental · Fabaceae
Sweet Pea
Lathyrus odoratus
Sow it early, cut it often, and the sweet pea pays you back with scent and color all spring.
Full sun
Every 2–4 days
39–64°F · 4–18°C
50–75 days
Overview
Few flowers carry a fragrance like the sweet pea. It's a fast-climbing annual in the pea family, sending up tendrils that grab any support you give them and covering it in ruffled blooms. The scent is the whole point, which is why gardeners have grown it for cut flowers for well over a century.
This is a cool-season plant through and through. It wakes up in the chilly weeks of early spring, flowers from May into July, and then fades once the heat arrives. That short, brilliant run is the trade-off for the color and perfume, and it rewards getting the seed in the ground early.
Sweet peas ask for a little work up front and steady attention after. Soak and nick the hard seeds, keep the soil evenly moist, and keep cutting the flowers to push out more. Skip the picking and the plant sets seed and quits, so the more you cut, the longer it blooms.
Care
The short version: full sun, rich and evenly moist soil on the alkaline side, cool growing weather, and constant cutting to keep the flowers coming.
Light
Sweet peas flower best in full sun, though they take a bit of afternoon shade where spring turns warm early. The more sun they get in cool weather, the heavier the bloom.
Water
Keep the soil evenly and consistently moist, watering roughly every 2 to 4 days and never letting plants dry out while they flower. Water at the base rather than over the top, and make sure the ground drains well so the roots don't sit wet.
Soil
Give them rich, humus-heavy soil that holds moisture but still drains, with plenty of organic matter dug in. They prefer it slightly alkaline, around a pH of 7.0 to 7.5.
Temperature
These are cool-weather plants, happiest between 39°F and 64°F (4°C to 18°C). Growth and flowering both fall off once it turns hot, which is why an early start matters so much.
Humidity
Average outdoor humidity suits them fine, so there's no number to hit. Airflow counts for more, since crowded, muggy conditions invite mildew and other leaf diseases.
Feeding
Feed with a balanced fertilizer about once a month through the growing season. Steady feeding keeps the plants vigorous and the flowers coming.
Pruning
Deadhead spent flowers and keep cutting blooms to push the plant into making more, since once it sets seed it stops. Pull the whole plant once it declines in the summer heat.
Size & spacing
Climbing types reach 3 to 8 feet (91 to 244 cm) tall and need a trellis or netting to scramble up. Each plant spreads about 2 to 3 feet (61 to 91 cm), so give them room for air to move.
When to plant
Sweet peas are built for cool weather and have no patience for heat. Start seeds indoors 6 to 8 weeks before your last frost or sow straight outside as soon as the soil can be worked, then enjoy the bloom from late spring until the summer heat shuts it down. In mild-winter areas, a fall sowing gives you flowers through 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 trouble is either the season ending or a few familiar pests. Learn to tell normal summer decline from a real problem, then match what you see below and act while it still helps.
Plants stop flowering and collapse as summer heats up
Sweet peas are cool-season annuals, so a fading, yellowing plant in early summer is the season ending, not a disease. Once the heat and humidity settle in, flowering stops for good. Pull the spent plants and, in warm regions, sow again in fall for winter and spring bloom.
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 holes in young shoots with slime trails nearby
Slugs and snails go after tender seedlings, leaving torn leaves and shiny trails, and they do the most damage in damp weather. Go out at dusk and pick them off by hand. Clear away leaf litter and other hiding spots, and ring young plants with a barrier or trap.
Fix:
- Handpick slugs and snails in the evening
- Reduce moist hiding spots and use barriers or traps around young plants
Curled new growth, clustered insects, and a powdery coating on leaves
Two problems often show up together here. Aphids and mites crowd onto the soft new growth and twist it, while powdery mildew, leaf spot, or rust coat the leaves once plants sit crowded and damp. Blast the aphids off with water, open the planting up for airflow, and keep water off the foliage.
Fix:
- Wash off aphids with water or treat as needed
- Improve air circulation and avoid overhead watering to reduce foliar disease
Toxicity
Despite the friendly name, sweet pea is a flower to look at, not to eat. The seeds and pods hold a neurotoxic amino acid that causes lathyrism, with weakness and lasting nerve and bone damage, in people, horses, and livestock who eat enough, plus stomach upset in cats and dogs. Keep the pods well away from children, pets, and grazing animals.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
A nibble of leaf or stem may bring on drooling, vomiting, and a sour stomach. The real risk is the seeds and pods, where a larger or repeated helping can lead to weakness and shaky, off-balance movement.
Dogs Mild
Chewing the foliage tends to cause vomiting and an upset gut. Dogs that crack open and swallow the pods or seeds are the ones at risk of weakness and the nervous-system signs of lathyrism.
Horses Toxic
Horses are hit hard. Eating the plant brings weakness, lethargy, restless pacing, head pressing, tremors, and seizures, and a bad case can be fatal.
Rabbits Toxic
The same neurotoxic amino acids in the seeds and pods make this plant unsafe for rabbits, so keep it well out of reach rather than offering any as forage.
Livestock Toxic
Cattle, sheep, and goats that graze the seeds over time develop lathyrism, with muscle weakness and lasting damage to the skeleton and nerves. Fence them away from the plants entirely.
Birds Toxic
The poisonous seeds and pods make sweet pea a poor choice around poultry and pet birds, which readily peck at seed. Keep the seed pods out of their reach.
People Caution
No part of this plant is food, despite the name. The pods and seeds are poisonous, and eating seeds over time can cause lathyrism, with weakness and nerve and bone damage, so keep children 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 peas come in groups bred for different things, some for size and stem length, others for pure scent. These are the ones worth knowing by name.
Spencer types
The classic exhibition and cut-flower group, carrying large, frilled, ruffled blooms on long stems.
Old-fashioned / Grandiflora types
Their blooms are smaller, but they hold the strongest, sweetest scent that gave the species its name.
Cupani / Matucana
This heirloom bicolor sits close to the wild original, with deep maroon and violet flowers and an intense fragrance.
Dwarf / bush types
Compact, mounding plants that need little or no support, which suits them to containers and edging.
How to propagate
Sweet peas grow from seed, and the only catch is a tough seed coat that needs a little help before it will sprout.
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 peas grow from seed, and the hard seed coat is the one hurdle. Nick or file each seed and soak it in warm water for about 24 hours before sowing to speed things along. Start indoors 6 to 8 weeks before your last frost, or sow straight into the ground in early spring once the soil can be worked, and in mild-winter areas sow in fall. Seeds sprout 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 not the edible garden pea, even though the pods look alike. Its seeds and pods are poisonous, and eating the seeds over time can cause lathyrism, a serious nerve and skeletal disorder. Grow it for the flowers and never for the table.
Sweet peas keep blooming all summer long.
These are cool-season annuals that flower from spring into early summer. Once the heat and humidity arrive, they decline fast and usually need pulling, so the show is a spring one, not a summer one.