Ornamental · Fabaceae
Sweet Pea
Lathyrus odoratus
Sow it early, cut it often, and the sweet pea keeps handing back scent and color all spring.
Full sun
Every 2–4 days
39–64°F · 4–18°C
50–75 days
Overview
Chasing fragrance in the garden? Sweet pea delivers like little else. This fast-climbing annual in the pea family flings out tendrils that latch onto any support and swarm it with ruffled blooms. That scent is the payoff, and it has kept gardeners sowing it for cut flowers for well over a century.
Everything about this plant runs on the cool season. It surges into growth through the chilly weeks of early spring, flowers hard from May into July, then winds down when the heat rolls in. That short, spirited run is the deal for so much color and perfume, and getting seed in early squeezes the most out of it.
Sweet peas ask for a burst of effort up front, then reward steady hands. Nick and soak the tough seeds, keep the soil evenly moist, and keep cutting the flowers to drive out more. Stop picking and the plant sets seed and calls it done, so lock in the golden rule: the more you cut, the longer it blooms.
Care
The short version: full sun, rich and evenly moist soil that leans alkaline, cool growing weather, and nonstop cutting to keep the flowers rolling in.
Light
Aim sweet peas at full sun and they flower their hardest, though they will shrug off a little afternoon shade where spring warms early. Pile on the sun in cool weather and the bloom answers back.
Water
Keep that soil evenly and consistently moist, watering about every 2 to 4 days, and never let the plants run dry while they flower. Water at the base, skip the overhead soak, and make sure the ground drains so the roots never stew.
Soil
Load them into rich, humus-heavy soil that holds moisture yet drains clean, packed with organic matter. Push the pH slightly alkaline, right around 7.0 to 7.5, and they hum along.
Temperature
These plants live for cool air, peaking between 39°F and 64°F (4°C to 18°C). Growth and flowering both stall once heat lands, which is exactly why an early jump pays off.
Humidity
Ordinary outdoor humidity is plenty, so forget chasing a number. Airflow is the real lever, since crowded, muggy pockets hand mildew and other leaf diseases an opening.
Feeding
Hit them with a balanced fertilizer about once a month through the growing season. Keep that rhythm going and the plants stay strong and the flowers keep firing.
Pruning
Deadhead the spent flowers and keep cutting fresh ones to drive the plant into making more, because the second it sets seed it downs tools. When summer heat finally beats it, yank the whole plant.
Size & spacing
Climbing types shoot to 3 to 8 feet (91 to 244 cm) and grab onto a trellis or netting to get there. Give each plant about 2 to 3 feet (61 to 91 cm) to spread so air can rip through the planting.
When to plant
Sweet peas thrive on cool weather and quit fast in heat, so nail the timing and the rest follows. Fire seeds off indoors 6 to 8 weeks before your last frost, or sow straight outside the moment the soil can be worked, then ride the bloom from late spring until summer heat shuts it down. Mild-winter gardeners can sow in fall and pull 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
Nearly every sweet pea hiccup traces back to one of two things: the season bowing out, or a handful of familiar pests. Learn to tell ordinary summer decline from a real problem, then match what you spot below and jump on it while it still helps.
Blooms cut out and plants keel over as summer heats up
Do not panic when a plant yellows and folds in early summer, because sweet peas are cool-season annuals and this is just the season signing off, not a disease. Once heat and humidity dig in, flowering is finished. Rip out the spent plants, and if you garden somewhere warm, sow again in fall to score 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
Chewed young shoots trailing telltale slime
That damage is slugs and snails hitting the tender seedlings, tearing leaves and leaving shiny trails, and they go wild in damp weather. Head out at dusk and pick them off by hand for the fastest win. Then clear leaf litter and other hiding spots, and ring the 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
Curling new growth, clustered bugs, and a powdery coating on leaves
Two problems love to gang up here. Aphids and mites pile onto the soft new growth and twist it, while powdery mildew, leaf spot, or rust creep over leaves left 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
Here is the one hard line with sweet pea: grow it, cut it, love it, but never eat it. The seeds and pods carry a neurotoxic amino acid that triggers lathyrism, with weakness and lasting nerve and bone damage, in people, horses, and livestock that 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 quick nibble of leaf or stem can leave a cat drooling, vomiting, and off its stomach. The bigger danger sits in the seeds and pods, where a larger or repeat helping can bring weakness and shaky, off-balance movement.
Dogs Mild
Chewed foliage usually means vomiting and an upset gut. Dogs that crack open and swallow the pods or seeds are the ones facing weakness and the nervous-system signs of lathyrism.
Horses Toxic
Horses take a serious hit. Eating the plant brings weakness, lethargy, restless pacing, head pressing, tremors, and seizures, and a bad case can turn 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 instead of 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 clear of the plants entirely.
Birds Toxic
The poisonous seeds and pods make sweet pea a bad neighbor for poultry and pet birds, which pounce on seed. Keep the seed pods well out of their reach.
People Caution
Despite the 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 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 split into a few spirited groups, each bred for a different prize, some for size and long stems, others for knockout scent. These are the ones to know by name.
Spencer types
The classic exhibition and cut-flower group, loaded with large, frilled, ruffled blooms on long stems.
Old-fashioned / Grandiflora types
The blooms run smaller, but they pack the strongest, sweetest scent, the very fragrance that named the species.
Cupani / Matucana
An heirloom bicolor sitting close to the wild original, firing off deep maroon and violet flowers with an intense fragrance.
Dwarf / bush types
Compact, mounding plants that need little or no support, which makes them a natural for containers and edging.
How to propagate
Sweet peas launch from seed with ease, and the only thing to beat is a tough seed coat that wants 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 rocket from seed once you clear the one hurdle: that hard seed coat. Nick or file each seed and soak it in warm water for about 24 hours before sowing to kick germination into gear. Start them indoors 6 to 8 weeks before your last frost, or sow straight into the ground in early spring the moment the soil can be worked, and in mild-winter areas sow in fall. Seeds break ground 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.
Look-alike pods fool plenty of people, but 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 nerve and skeletal disorder. Grow this one for the flowers and keep it far from the table.
Sweet peas bloom all summer long.
Not a chance, since these are cool-season annuals that flower from spring into early summer. Once heat and humidity move in they crash fast and usually need pulling, so bank on a spring show, not a summer one.