Ornamental · Fabaceae
Sweet Pea
Lathyrus odoratus
Get the seed in early, keep picking, and the sweet pea gives back scent and color all spring.
Full sun
Every 2–4 days
39–64°F · 4–18°C
50–75 days
Overview
Not many flowers greet you with a scent like the sweet pea. It is a fast-climbing annual in the pea family, sending out tendrils that happily grab hold of whatever support you offer and clothing it in soft, ruffled blooms. That fragrance is the real reason to grow it, and gardeners have leaned on it for cut flowers for well over a century, so you are in good company.
This is a cool-season plant at heart, and understanding that makes everything easier. It stirs to life in the chilly weeks of early spring, flowers from May into July, then bows out when the heat rolls in. That short and lovely run is simply the deal you make for so much color and perfume, and getting the seed in early is what earns you the most of it.
Sweet peas ask for a bit of care at the start and some steady attention after, and none of it is hard to get right. Nick and soak the tough seeds, keep the soil evenly moist, and keep snipping the flowers to coax out more. If picking slips your mind the plant sets seed and calls it a season, so remember that the more you cut, the longer it blooms, and a missed day or two is easily forgiven.
Care
The short version: give them full sun, rich and steadily moist soil that leans a touch alkaline, cool growing weather, and plenty of cutting, and the flowers will keep coming.
Light
Sweet peas bloom their best in full sun, though they will gladly take a little afternoon shade where spring warms up early. The more sun they soak up while the weather stays cool, the more generous the flowering.
Water
Keep the soil evenly and steadily moist, watering around every 2 to 4 days and never letting the plants go dry while they are in flower. Water gently at the base rather than over the leaves, and make sure the ground drains freely so the roots are never left sitting wet.
Soil
Treat them to rich, humus-heavy soil that holds moisture yet still drains, worked through with plenty of organic matter. They are happiest when it leans slightly alkaline, somewhere around a pH of 7.0 to 7.5.
Temperature
These are cool-weather plants, most content between 39°F and 64°F (4°C to 18°C). Both growth and flowering ease off once things heat up, which is exactly why an early start pays you back so well.
Humidity
Ordinary outdoor humidity suits them just fine, so there is no target number to chase. Good airflow matters far more, since crowded, muggy pockets are what invite mildew and other leaf troubles.
Feeding
Offer a balanced fertilizer about once a month right through the growing season. That steady feeding keeps the plants strong and the blooms arriving.
Pruning
Deadhead the spent flowers and keep cutting fresh ones, which nudges the plant into making still more, since it stops the moment it sets seed. When it finally tires in the summer heat, lift the whole plant and let it go.
Size & spacing
Climbing kinds reach 3 to 8 feet (91 to 244 cm) tall and will want a trellis or netting to clamber up. Each plant takes up about 2 to 3 feet (61 to 91 cm) of room, so leave space for air to drift through.
When to plant
Sweet peas love cool weather and simply will not wait out the heat, so timing is your friend here. Start seeds indoors 6 to 8 weeks before your last frost, or sow them straight outdoors as soon as the soil can be worked, and you will have blooms from late spring right until summer heat calls time. Where winters stay mild, a fall sowing rewards you with flowers through winter and into 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 worries turn out to be either the season quietly ending or one of a few familiar pests, and both are manageable. Learn to tell ordinary summer fade from a genuine problem, then find what you are seeing below and act while it still does some good.
Blooms fade and plants collapse as summer warms up
Take heart, because a cool-season annual that yellows and fails in early summer is just reaching the natural end of its season, not catching a disease. Once the heat and humidity settle in for good, flowering is finished. Gently pull the tired plants, and if you garden somewhere warm, sow a fresh batch in fall for winter and spring blooms.
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
Torn young shoots with shiny trails left nearby
Slugs and snails love tender seedlings, chewing ragged leaves and leaving glistening trails, and they are busiest in damp spells. The simplest fix is to step out at dusk and pick them off by hand. Tidy away leaf litter and other cool hiding places, and ring your young plants with a barrier or a trap for good measure.
Fix:
- Handpick slugs and snails in the evening
- Reduce moist hiding spots and use barriers or traps around young plants
Curling new growth, clustered bugs, and a powdery film on leaves
Two little problems often turn up hand in hand here. Aphids and mites gather on the soft new growth and twist it out of shape, while powdery mildew, leaf spot, or rust settle on leaves that sit crowded and damp. A firm spray of water knocks the aphids off, thinning things out restores airflow, and keeping water off the leaves does the rest.
Fix:
- Wash off aphids with water or treat as needed
- Improve air circulation and avoid overhead watering to reduce foliar disease
Toxicity
For all its gentle name, the sweet pea is a flower to enjoy with your eyes, not your fork. Its seeds and pods carry a neurotoxic amino acid that causes lathyrism, bringing weakness and lasting nerve and bone damage, in people, horses, and livestock who eat enough, along with an upset stomach in cats and dogs. Keeping the pods well away from children, pets, and grazing animals is all it takes to stay safe.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
A curious nibble of leaf or stem can bring on drooling, vomiting, and a queasy stomach. The greater worry is the seeds and pods, where a larger or repeated helping may lead to weakness and shaky, unsteady movement.
Dogs Mild
A mouthful of foliage usually means vomiting and a bit of a stomach upset. It is the dogs that crack open and swallow the pods or seeds who face weakness and the nervous-system signs of lathyrism.
Horses Toxic
Horses take it hard. Eating the plant brings on weakness, lethargy, restless pacing, head pressing, tremors, and seizures, and a severe case can prove 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 ever offering it as forage.
Livestock Toxic
Cattle, sheep, and goats that graze the seeds over time develop lathyrism, with muscle weakness and lasting harm to the skeleton and nerves. Fence them away from the plants completely.
Birds Toxic
Those poisonous seeds and pods make sweet pea a poor neighbor for poultry and pet birds, which are quick to peck at seed. Keep the seed pods well out of their reach.
People Caution
Despite the inviting name, no part of this plant is food. The pods and seeds are poisonous, and eating seeds over time can cause lathyrism, with weakness and damage to nerve and bone, 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 arrive in a few groups, each bred with a different goal in mind, some chasing size and long stems and others chasing pure scent. Here are the ones worth getting to know by name.
Spencer types
This is the classic exhibition and cut-flower group, prized for large, frilled and ruffled blooms carried on long stems.
Old-fashioned / Grandiflora types
The blooms here run smaller, yet they hold the strongest, sweetest scent, the very fragrance that gave the species its name.
Cupani / Matucana
An heirloom bicolor that sits close to the wild original, showing deep maroon and violet flowers with an intense fragrance.
Dwarf / bush types
These are compact, mounding plants that need little or no support, which makes them a natural fit for containers and edging.
How to propagate
Sweet peas grow happily from seed, and the only real catch is a tough seed coat that appreciates 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 readily from seed, and that hard seed coat is the single hurdle to clear. Nick or file each seed and give it a soak in warm water for about 24 hours before sowing, and germination speeds right up. Start them indoors 6 to 8 weeks ahead of your last frost, or sow straight into the ground in early spring once the soil can be worked, and in mild-winter regions sow in fall instead. The seeds come up in roughly 1 to 3 weeks, and the first flowers open about 50 to 75 days after sowing.
Myths
Sweet pea seeds and pods can be eaten just like garden peas.
As alike as the pods look, the ornamental sweet pea is not the edible garden pea. Its seeds and pods are poisonous, and eating the seeds over time can cause lathyrism, a serious disorder of the nerves and skeleton. Grow this one purely for its flowers, and never for the kitchen.
Sweet peas will flower right through the whole summer.
They are cool-season annuals, blooming from spring into early summer and no further. Once the heat and humidity arrive they decline fast and usually need pulling, so think of the display as a glorious spring one rather than a summer-long show.