How to Plant and Grow Sweet Pea

Sweet peas are among the garden flowers you can smell before you see them. These easy-to-grow annual vines unfurl delicate blossoms in spring or early summer, perfuming the garden with a pleasing sweet, spicy fragrance. They love cool weather and will wither as soon as the heat of summer sets in. Even with their short growing season in most regions, sweet peas are a prized member of the flower garden and a coveted cutting flower for bouquets. Popular—to the point of obsession—with gardeners at the turn of the 20th century, sweet peas were the highlight of elaborate plant expositions and the sole focus of some plant societies. Gardeners collected and grew all colors and shapes of the boldly fragrant blossoms. Although they are not as commonly grown today, once you experience the intoxicating fragrance of sweet peas in a twilight garden, you’ll likely plant your own crop year after year. 

Sweet peas are toxic to humans and pets.

Where to Plant Sweet Pea

Plant sweet peas in full sun to partial shade and rich, well-drained, neutral to alkaline soil.

Because the vines need a trellis or a wire fence, sweet peas are usually grown in rows. They are a natural choice for a cutting or a kitchen garden. You can also plant them in a vegetable garden but do not plant them next to edible garden peas and clearly mark them because sweet peas are toxic.

Wherever you plant sweet peas, keep in mind that they decline rapidly after the bloom so have another late-blooming annual, such as marigold, celosia, or zinnia lined up to fill the bare space.

How and When to Plant Sweet Pea

The planting time of sweet peas depends on the severity of your winters. When properly timed, sweet peas do all their growing and blooming before the summer heat sets in. If you live in a climate where the ground does not freeze, plant sweet peas in October or November for a March bloom. If your winter is moderately cold, plant them in January or February. In climates with subzero winters, plant sweet peas as soon as the soil can be easily worked in the spring, or start them indoors 6 to 7 weeks before the last frost date in your area.

To improve germination, make a tiny cut in the hard seed coat using nail clippers. This will let the seed absorb moisture. Sow the seeds 1 inch deep and 2 to 3 inches apart. Depending on the weather and soil temperature, germination takes between 10 and 28 days.

Once the seedlings are a few inches tall, thin them to 5 to 6 inches apart. If your climate is humid, space them further apart for better air circulation.

Sweet Pea Care Tips

The proper planting time is crucial but other than that, taking care of sweet peas is not difficult.

Light

Plant sweet peas in full sun, except in climates with early very hot summers, where afternoon shade is beneficial.

Soil and Water

Before planting, enrich the soil with aged manure or compost. This will also improve drainage, as sweet peas need well-drained soil. Sweet Peas grow best in a pH between 7.0 and 7.5. Spread a 2-inch-thick layer of mulch around the plants.

Watering the sweet peas at all stages—from the germination of seeds to the blooming vines—is important. Water in the absence of rain whenever the top inch of soil feels dry.

Temperature and Humidity

Sweet peas are cool-season bloomers that can handle light frosts. The ideal temperature is between 65 and 80 degrees F. They do poorly in hot weather and high humidity.

Fertilizer

Even if you start them in rich soil, sweet peas need to be fertilized at least twice during their short growing season. It is best to use a liquid fertilizer, such as fish emulsion or liquid kelp, or a combination of the two, always diluting it well in water.

Pruning

When the seedlings have three or four sets of leaves, pinch off the top leaves, which encourages branching and produces more flower stems.

Potting and Repotting

If you want to grow sweet peas in a pot, select short, non-climbing dwarf varieties such as ‘Bijou’ that don’t grow taller than 10 inches and won’t require support.

Make sure the pot has large drainage holes and fill it with a mix of well-draining potting mix and a few handfuls of compost mixed in.

Keep in mind that potted plants need more frequent watering than inground plants. Also, potted sweet peas should be fertilized with a liquid fertilizer every two weeks.

Repotting won’t be required as sweet peas are annuals.

Pests and Problems

Sweet pea seedlings are a favorite snack for birds, slugs, and snails, especially if planted in fall. Protect seedlings with netting once they are 4 to 5 inches tall or sprinkle them with diatomaceous earth.

Aphids, another common pest on sweet peas, can be washed off with water from a hose.

Powdery mildew is also common. To prevent it early in the plant’s life cycle, ensure good air circulation around foliage and avoid watering in the evening. After the bloom at the end of their life cycle, the plants often inevitably get powdery mildew.

How to Propagate Sweet Pea

Sweet peas are propagated from seeds as described above. Note that depending on the variety, seed pods collected from sweet peas in your garden will not necessarily produce plants that are true to type—only heirloom sweet peas will—so you might be better off starting with seeds from a seed company.

Leave the seeds pods on the plants until they are fully mature and light brown in color. Don’t wait too long though, or the pods will split open and disperse the seeds. Bring the pods indoors and let them air dry in a warm place but out of direct sunlight for a few days. Place the pods in a paper bag and shake it vigorously to break open the pods and release the seeds. Place the seeds on a tray and sort out any damaged ones. Store the seeds in an envelope in a cool and dry place until planting time.

Types of Sweet Pea

The number of sweet pea varieties and their classification can be a bit overwhelming. There are Spencer, Grandiflora, Royal, Early Multiflora, Gigantea, Cuthbertson, Hammett, dwarf, semi-dwarf, and intermediate sweet peas. Here are some popular varieties valued for their visual appeal and fragrance:

‘Matucana’

The bicolored violet and deep maroon colors are smaller than those of other varieties. This old heirloom variety that goes back to 1700 makes up for it with a long bloom time.

‘Painted Lady’

This is another early heirloom variety with rose, pastel pink, and cream bicolored flowers. It is considered fairly heat-tolerant. 

‘Noel Sutton’

A Spencer-type variety, this sweet pea has large blue flowers and long, firm stems, which makes it a good cutting flower. 

‘Almost Black’

The darkest of all sweet peas, the flowers of this Grandiflora are small but striking. The color is described as very dark navy, violet-maroon, or purple-black. 

‘King Edward VII’

This vigorous grower has strongly scented crimson or vivid red flowers. It was introduced in 1903 during the height of the sweet pea craze in England and was named after the ruling king.

Sweet Pea Companion Plants

Sweet Alyssum

Valued for its early spring flowers, sweet alyssum is a cool-season annual with dainty blossoms on tidy mounds of foliage. Sweet alyssum flowers are most often found in a crisp, clean white. Plant sweet alyssum in a place where it gets full sun although in warmer climates partial shade is also acceptable. It needs excellent drainage.

Pansies

More clumping than spreading, these annuals fit well in the space at the base of sweet peas. Both pansies and sweet peas do best in cool weather, which makes them excellent companions for spring planting. Pansies come in a variety of colors, ranging from cool hues like blue and purple to warm colors like orange, red, pink, and even black and white.

Climbing Rose

Sweet peas and climbing rose, a perennial, easily share a trellis and their growing conditions are very similar. They should be planted where they receive full sun for most of the day and they need well-draining soil that is rich and loamy. Climbing rose blooms later, between summer and fall so you’ll have an ongoing display of flowers on the trellis. Zone 4-11