Sweet pea is a staple of flowering climbers and has been since the Victorian era. The sweet pea, which uses tendrils to climb when correct supports are available, grows to a height of 1.02 m – 2 m. The highly fragrant flowers are purple when found in the wild, but domesticated cultivars can be found in nearly every color.
I. Appearance and Characteristics
The sweet pea, Lathyrus odoratus, is a flowering plant in the genus Lathyrus in the family Fabaceae (legumes), native to Sicily, southern Italy and the Aegean Islands.
It is an annual climbing plant, growing to a height of 1–2 metres (3 ft 3 in – 6 ft 7 in), where suitable support is available. The leaves are pinnate with two leaflets and a terminal tendril, which twines around supporting plants and structures, helping the sweet pea to climb. In the wild plant the flowers are purple, 2–3.5 cm (3⁄4–1+1⁄2 in) broad; they are larger and highly variable in color in the many cultivars. Flowers are usually strongly scented.
The annual species, L. odoratus, may be confused with the everlasting pea, L. latifolius, a perennial.
Sweet peas have been cultivated since the 17th century and a vast number of cultivars are commercially available. They are grown for their flower color (usually in pastel shades of blue, pink, purple and white, including bi-colours), and for their intense unique fragrance. They are grown by gardeners for private enjoyment or for exhibition, and in the floristry trade. The large, pea-shaped seeds are sown in cold frames in Spring or Autumn.
The seeds benefit from pre-soaking or chipping with a sharp blade. The plants are also available later in the season, as young plants or plugs. They are grown up canes, with the new shoots being regularly pinched out to promote a bushy habit and higher flower yields. Plants typically reach heights of 1–2 meters (3 ft 3 in – 6 ft 7 in), with the flowers appearing in midsummer and continuing for many weeks if regularly deadheaded.
Over 50 cultivars have gained the Royal Horticultural Society’s Award of Garden Merit.
Unlike the edible pea, there is evidence that seeds of members of the genus Lathyrus are toxic if ingested in quantity. A related species, Lathyrus sativus, is grown for human consumption but when it forms a major part of the diet it causes symptoms of toxicity called lathyrism.
In studies of rats, animals fed a diet of 50% sweet pea seeds developed enlarged adrenals relative to control animals fed on edible peas. The main effect is thought to be on the formation of collagen. Symptoms are similar to those of scurvy and copper deficiency, which share the common feature of inhibiting proper formation of collagen fibrils. Seeds of the sweet pea contain beta-aminopropionitrile that prevents the cross-linking of collagen by inhibiting lysyl oxidase and thus the formation of allysine, leading to loose skin. Recent experiments have attempted to develop this chemical as a treatment to avoid disfiguring skin contractions after skin grafting.
II. How to Grow and Care
Sunlight
Sweet peas thrive in full sun, although in warmer climates, they do well in a location that receives a bit of shade in the afternoon’s heat.
Temperature and Humidity
Because sweet peas originated in the Mediterranean, they can handle an occasional chill but do best if planted after the last frost and in warmer temperatures in USDA zones 3-8. Sweet pea seedlings can tolerate a light frost, but the plants dislike sweltering temperatures. Plant early to enjoy the blooms before they wither in the heat.
Watering
Sweet pea only has high watering needs during its growing season, when it prefers consistently moist soil. Without flooding the soil, give your Sweet pea a deep drink whenever the soil surface feels mostly dry. Do not water overhead, as that puts the vines at risk of fungal infection.
Fertilizing
Sweet pea plants need loads of nutrients during their flowering period, so that is the time you’ll want to supply them with fertilizer. Once the flowers start to come out, begin fertilizing the soil with a balanced fertilizer or compost every 2 weeks until the flowers are spent.
How to Plant and Soil
Plant sweet peas in the late winter and early spring. Sow three seeds together about a foot between groups of seeds. Plant sweet pea seeds about 1 inch down in the soil. Work compost into the soil about six weeks before planting the seeds for better blooms. Compost will also improve poor soil.
Sweet peas prefer rich but well-drained soil. A slightly alkaline soil pH (about 7.5) is ideal.
Pruning
To increase branching, which produces more flowering stems, pinch the growing tips back 1 inch when the plant reaches 4 inches tall.3 The more you cut the flowers, the more blooms you should get, so don’t hesitate to bring some bouquets indoors. Deadhead the spent flowers to encourage continued blooming.
Propagation
Sweet peas are best grown from seeds; however, you can use seedling cuttings if you do not have seeds yet and want to produce more plants. The cuttings will catch up to soil-grown plants if taken in the early spring.
- What You’ll Need: Jar of water, scissors, healthy seedling segment, root hormone (optional)
- Cut a 5 or 6-inch stem segment from a healthy seedling; cut just above a pair of leaves, leaving at least a few nodes to allow for new growth.
- Optionally give rooting hormone to promote healthier, more robust rooting success. If using it, dip the cut end of the stem into the hormone for five seconds, then put the cut end in the jar of water and place it in a spot that receives indirect sunlight.
- Once you notice root growth, usually between 7 to 14 days, you can plant each rooted stem cutting in soil. It’s best to give the plant a greenhouse-like environment, such as placing a plastic bag over the cutting. Give it about an hour of fresh air daily. Wait until you notice new, vigorous growth; it can take about six weeks, then transplant it into the ground or a larger container outdoors.
How to Grow From Seed
Sweet peas are usually direct sown. You can get a jump start on the season by starting seed indoors about four to five weeks before your last frost date. Seed can be started outdoors when the ground has warmed to about 50 degrees Fahrenheit and is not too wet. In the South, you may have better luck seeding sweet peas in the fall to grow into winter.
- Seeds should be scarified by nicking or soaking in water for several hours to soften the seed coating to assist germination.
- They will be easier to transplant if you start them in peat pots.
- Seeds germinate in soil temperatures from 55 to 65 F. Plant seeds in holes about two inches deep. Drop two to four seeds per hole, with holes spaced four to six inches apart.
- Water thoroughly and keep the soil moist until seeds have sprouted.
- When you are ready to transplant, pinch any flowers or buds that may have formed, encouraging root development.
- Pinch the seedlings to encourage vigorous side shoots when the plants reach about 4 inches tall in the garden.
Sweet pea vines have tendrils and will attach to almost any type of support with meshing or strings.
Potting and Repotting
Sweet peas can also be potted into planters and placed indoors. With just a few steps, you can have a lovely new pea plant for your home.
You must remove the nursery plant from its container and then brush off the excess soil from its roots. After most excess soil is shaken off, place the plant into a larger planter and repot the soil back into it. Feel free to tease the roots if they are clumped together.
When placing the soil into the planter, press down the soil to remove air bubbles for maximum growth.
Pests and Diseases
Common Pests
Few pests or problems are associated with sweet peas, although aphids, mites, and pea moths are occasional pests. Slugs and snails can also eat new plants.
Common Problems
Sweet peas grow easily with suitable environmental factors. However, certain problems can arise if growing conditions are off.
Bud Drop
High temperatures are the No. 1 reason for plant decline. However, if you notice buds dropping, check the soil; it should be moist but not soggy. Also, ensure the plant has at least six to eight hours of full sun. Do not give more fertilizer to correct the problem; sometimes, too much fertilizer is the problem.
Yellowing Leaves
When a plant is overwatered, it’s common for leaves to start turning yellow. Reduce watering or check the soil with your finger to ensure the soil is not waterlogged. Also, giving too much fertilizer can burn the roots, resulting in yellowing leaves.
III. Uses and Benefits
Sweet pea is a popular annual used as a climber or in pots or beds. As a climber, it will need to be staked, or it will run over the ground. With many colors to choose from, gardeners often mix and match colors for a striking floral display in pollinator gardens. Good companion plants are sweet alyssum, lavender, and catmint.
IV. Types of Sweet Peas
Another plant sweet pea shrub (Polygala spp.) is unrelated to the sweet pea plant (Lathyrus odoratus) but gets its name from its similar-looking flowers.
- Cultivars of sweet pea plants (Lathyrus odoratus) include:
- ‘Old fashioned’: Sweet peas labeled old fashioned should be fragrant.
- Spencer cultivars: These are exceptionally hardy vines with striking coloring, but not all of them are particularly fragrant.
- ‘Bijou Group’: This is a sweetly scented dwarf variety for containers.
Find Where to Buy the Best Sweet Pea (Lathyrus odoratus)
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