How to Grow Annual Sweet Pea Flowers

Photo by: Paul Burr / Shutterstock.

Where to plant:

Native to the Mediterranean, sweet peas are happiest when grown in full sun (at least 6 hours daily). In warmer climates, they can benefit from a bit of afternoon shade to help keep them cool.

When to plant:

The secret to success with sweet peas is to plant them early because the seeds must be sown in cool weather. If you live in Zone 8 or warmer, sow seeds in late fall for early spring blooms. In colder climates, sow in early spring as soon as the ground can be worked.

How to plant:

Although you can grow sweet peas from purchased plants, you’ll have a much broader selection of cultivars if you start your plants from seed. Sow the seeds in furrows 1 inch deep, spacing them 2 to 3 inches apart. Water thoroughly, and keep the soil moist until the seeds have sprouted. Expect germination to take 12 to 28 days, depending on the soil temperature.

To improve germination success, nick the hard seed coats with a nail clipper before planting or soak them in water for 24 hours so moisture can penetrate more easily when germinating.

Note: Save your sweet pea seeds! Leave flowers in place until they fade and allow the seed pods to form. Check seed pods often, and harvest them after they turn brown and brittle. You'll want to catch them before they open and drop their seeds, but not too early or the seeds won't germinate. Pop open the seed pods, remove the seeds, and allow them to dry for 2 to 3 days. Then, store them in a cool, dry place for planting next year or in the freezer for at least 5 years.

Starting seeds indoors:

To extend the bloom time of sweet peas, start the seeds indoors 6 to 8 weeks before the last spring frost date. Plant the seeds in biodegradable pots in a soilless all-purpose potting mix, placing two or three seeds in each pot. Keep the soil evenly moist, and place the pots in a brightly lit location or under grow lights. Once the ground thaws and the soil is workable, transplant the pots directly into the garden so you won't disturb the roots. A light frost will not damage newly planted seedlings.

Spacing:

Because sweet peas are susceptible to powdery mildew, sufficient spacing of plants is important for good air circulation. When the seedlings are about 4 inches tall, thin them to a distance of at least 6 inches apart.

Tip:

To create a lattice wall of sweet pea vines, attach some wire mesh, string, or heavy-duty polypropylene netting to vertical stakes spaced several feet apart and allow the tendrils to weave through the grid. As the vines grow, you can secure any stray or wayward shoots to the support using garden twine. It doesn’t take long for sweet peas to climb, so be sure to install your supports at planting time. Learn more: Growing and Arranging Sweet Peas.

Cupani sweet peas. Photo by: pjhpix / Shutterstock.

Watering:

Sweet pea plants need consistent watering, especially during dry spells. Water plants regularly to keep the soil evenly moist but not soggy, providing about an inch of water a week if rainfall is insufficient. To prevent mildew problems, it’s best to water your plants at soil level or by using a drip irrigation system. Also avoid watering in the late afternoon and evening.

Amendments and fertilizer:

Sweet peas thrive in rich soil, so work in plenty of compost and organic matter before planting. They also need regular fertilization throughout the growing season to keep the blooms coming. Avoid using nitrogen-rich fertilizers, which will promote leaf growth instead of flowering. Instead, use a fertilizer higher in potassium or phosphorus, such as a blend formulated for tomatoes.

Pruning and deadheading:

When young sweet pea plants have developed four to six leaves, pinch back the growing tips by an inch or two to encourage bushier growth with lots of flowering side shoots. Once your sweet peas start blooming, do not let the flowers go to seed. Cut or deadhead them regularly to promote the production of more flowers and keep your plants looking their best. Toward the end of the growing season, you can leave some seedpods on the plant if you want to collect the seeds to sow next year.

Pests and diseases:

Sweet peas can be susceptible to aphids, thrips, garden slugs, and powdery mildew. Birds can also be a threat and may eat tender young seedlings and transplants. To protect your plants, place plastic berry baskets or bird netting over them until they are more mature.

'Sir Jimmy Shand' sweet pea. Photo by: Andrew Fletcher / Shutterstock.

If you shop around for annual sweet peas in seed catalogs or from online vendors, you’ll come across a dizzying array of selections, ranging from modern hybrids to heirloom varieties that have been around for centuries. To help you sort through your options, here’s a look at some of the most common types of sweet peas and the unique attributes of each.

Spencer:

Spencers are valued for their large frilly flowers, long stems, and wide array of colors and patterns, including bicolored, streaked, and picotee varieties. They are considered to be a “summer flowering” sweet pea, which means they need at least 12 hours of daylight in order to bloom. They may perform poorly in warmer climates, where summer temperatures often become too hot before a 12-hour day is reached. One of the most stunning Spencer varieties is ‘Sir Jimmy Shand’, which has creamy white flowers with lilac accents and picotee edges.

Grandiflora:

Among the most fragrant of the sweet peas, grandifloras have plain or slightly wavy petals, rather than the ruffles seen on Spencers. More recent, modern grandiflora hybrids combine the strong fragrance and colorful blooms of the original heirloom types with larger flowers and longer stems, making them wonderful for cutting. Two varieties to try include ‘Almost Black’, which bears masses of highly scented dark maroon flowers, and ‘Erewhon’, a bicolored bloomer with dark lavender-blue and soft pink petals.

Early multiflora:

Sometimes called “winter flowering” sweet peas, these types flower with as few as 10 hours of day length. They are a great choice for warm Southern climates because they can be bought into bloom before summer heat intensifies. Most often sold as part of a series, such as Winter Sunshine and Winter Elegance.

Dwarf and semi-dwarf:

Dwarf and semi-dwarf bush-type sweet peas have a compact habit and are equally at home in window boxes, containers, and garden borders. Dwarf varieties, such as the Cupid series, reach a height of only 8 to 10 inches. Semi-dwarf types (also called “intermediates”) grow to heights of 2 to 3 feet and include cultivars such as 'Explorer' and 'Knee High'.