Ornamental · Fabaceae
Sweet Pea
Lathyrus odoratus
Get it in early, keep cutting, and sweet pea hands back scent and color all spring.
Full sun
Every 2–4 days
39–64°F · 4–18°C
50–75 days
Overview
There's really nothing like the smell of a sweet pea. It's a fast-climbing annual in the pea family, and it throws out tendrils that'll grab onto whatever support you give them, then covers the whole thing in ruffled blooms. The scent is the whole point, honestly, and it's why folks have grown these for cutting for well over a century.
This one's a cool-season plant, through and through. It gets going in the chilly weeks of early spring, flowers from May into July, and then calls it quits once the heat shows up. Sure, that's a short run, but that's the deal you make for all that color and perfume, and it's exactly why getting seed in the ground early pays off.
Sweet peas want a little effort up front and some steady attention after that. Soak and nick those hard seeds, keep the soil evenly moist, and keep snipping the flowers so it makes more. Forget to pick and it'll set seed and stop, so here's the trick: the more you cut, the longer it blooms.
Care
The short version: full sun, rich soil that stays evenly moist and leans a bit alkaline, cool weather, and lots of cutting to keep those flowers coming.
Light
Sweet peas flower best in full sun, though they'll take a little afternoon shade where spring warms up early. Basically, the more sun they get while it's still cool, the more flowers you'll see.
Water
Keep the soil evenly and consistently moist, watering about every 2 to 4 days, and don't ever let them dry out while they're flowering. Water down at the base instead of over the top, and make sure the ground drains well so the roots aren't sitting in water.
Soil
Give them rich, humus-heavy soil that holds moisture but still drains, with plenty of organic matter worked in. They like it a touch alkaline too, somewhere 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). Once it heats up, both the growth and the flowering slow right down, which is why starting early matters so much.
Humidity
Regular outdoor humidity is totally fine, so there's no number to worry about. What actually matters is good airflow, since crowded, muggy spots are what bring on mildew and other leaf problems.
Feeding
Feed them a balanced fertilizer about once a month all through the growing season. Keep that going and the plants stay strong and the flowers keep coming.
Pruning
Deadhead the spent flowers and keep cutting the good ones, because that pushes the plant to make more, and once it sets seed it just stops. When it finally fades in the summer heat, pull the whole thing.
Size & spacing
The climbing types get 3 to 8 feet (91 to 244 cm) tall, so they'll need a trellis or some netting to climb. Each plant takes up about 2 to 3 feet (61 to 91 cm), so leave room for air to move through.
When to plant
Sweet peas love it cool and just can't handle heat, so timing really is the whole game. Start seeds indoors 6 to 8 weeks before your last frost, or sow them straight outside as soon as the soil's workable, and you'll get blooms from late spring until the summer heat shuts things down. Got mild winters? A fall sowing gets 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 of the time, sweet pea trouble is either the season wrapping up or one of a few usual-suspect pests. So the first job is telling normal summer fade apart from an actual problem, then matching what you're seeing below and acting while it still does some good.
Blooms quit and plants flop as summer warms up
Here's the good news: since sweet peas are cool-season annuals, a yellowing plant that's fading in early summer is just the season ending, not some disease. Once the heat and humidity really settle in, the flowering's done for good. So pull the tired plants, and if you're somewhere warm, sow again 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
Chewed-up young shoots with shiny trails right nearby
That's slugs and snails going after the tender seedlings, leaving torn leaves and shiny trails behind, and they're worst when it's damp out. Easiest thing? Head out at dusk and pick them off by hand. Then clear away leaf litter and other hiding spots, and put a barrier or trap around the young plants.
Fix:
- Handpick slugs and snails in the evening
- Reduce moist hiding spots and use barriers or traps around young plants
Curled new growth, clustered bugs, and a powdery film on the leaves
You've usually got two things happening at once here. Aphids and mites pile onto the soft new growth and twist it up, while powdery mildew, leaf spot, or rust settle on the leaves once plants get crowded and damp. Just blast the aphids off with water, open things up so air can move, 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
Don't let the sweet name fool you: this is a flower to look at, not to eat. The seeds and pods carry a neurotoxic amino acid that causes lathyrism, which means weakness and lasting nerve and bone damage, in people, horses, and livestock that eat enough, plus an upset stomach for cats and dogs. Just keep the pods away from kids, pets, and grazing animals and you're fine.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Mild
A little nibble of leaf or stem can leave a cat drooling, throwing up, and dealing with a sour stomach. The bigger worry is the seeds and pods, where a larger or repeat helping can bring on weakness and shaky, unsteady movement.
Dogs Mild
Chewing the foliage usually just means vomiting and an upset gut. It's the dogs that crack open and swallow the pods or seeds that risk weakness and the nervous-system signs of lathyrism.
Horses Toxic
Horses really get hit hard by this one. Eating the plant brings weakness, lethargy, restless pacing, head pressing, tremors, and seizures, and a bad case can even be fatal.
Rabbits Toxic
Those same neurotoxic amino acids in the seeds and pods make this plant unsafe for rabbits, so keep it well out of reach and don't ever offer any as forage.
Livestock Toxic
Cattle, sheep, and goats that graze the seeds over time end up with lathyrism, which means muscle weakness and lasting damage to the skeleton and nerves. Fence them right away from the plants.
Birds Toxic
The poisonous seeds and pods make sweet pea a bad pick around poultry and pet birds, since they'll happily peck at seed. Keep those seed pods 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 kids 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 a handful of groups, and each one's bred for something different, whether that's big flowers on long stems or just pure scent. Here are the ones worth knowing by name.
Spencer types
This is the classic exhibition and cut-flower group, and you'll know it by the large, frilled, ruffled blooms sitting on long stems.
Old-fashioned / Grandiflora types
The blooms are smaller here, but they've got the strongest, sweetest scent, the very thing that gave the species its name.
Cupani / Matucana
This heirloom bicolor is close to the wild original, showing off deep maroon and violet flowers with a really intense fragrance.
Dwarf / bush types
These are compact, mounding plants that need little or no support, which makes them great for containers and edging.
How to propagate
Sweet peas grow from seed, no problem, and the only real snag is a tough seed coat that needs a bit of help before it'll 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 that hard seed coat is really the only hurdle. Nick or file each seed and soak it in warm water for about 24 hours before you sow, and that speeds things right up. Start them indoors 6 to 8 weeks before your last frost, or sow straight into the ground in early spring once the soil's workable, and if your winters are mild, sow in fall instead. The seeds come up in about 1 to 3 weeks, and the first flowers open around 50 to 75 days after sowing.
Myths
Sweet pea seeds and pods are edible, just like garden peas.
Even though the pods look the same, the ornamental sweet pea isn't the edible garden pea. Its seeds and pods are poisonous, and eating the seeds over time can cause lathyrism, which is a serious nerve and skeletal disorder. So grow it for the flowers, and never for the table.
Sweet peas keep blooming all summer long.
Nope, these are cool-season annuals that flower from spring into early summer. Once the heat and humidity roll in, they fade fast and usually need pulling, so it's a spring show, not a summer one.