2005: Year of the Sweet Pea

Each year the National Garden Bureau selects a flowering plant to promote, and 2005 has been designated by that organization as "The Year of the Sweet Pea." In spite of the fact our summers are a bit warm by sweet pea’s standards, it is a unique annual well worth the effort to grow. Sweet pea flowers are vividly

Gwendoline variety sweet pea Photo by the National Sweet Pea Society of Great Britain.

colored and have airiness about them making them appear like small butterflies aflutter. Equally appealing is their captivating fragrance, often described as a blend of honey and orange blossom. Add fact that sweet peas are long-lived as cut flowers, and it is no wonder they are regarded by some as the "Queen of the Annuals." The English poet Keats supposedly first used the common name "sweet pea" in the early 19th century. Today, both English and North Americans use this common name to refer to Lathyrus odoratus. Sweet pea is a member of the Leguminosae (legume) family and belongs to the genus Lathyrus. The latter is commonly known as the vetchling or wild pea genus and is comprised of 110 species and innumerable cultivars. Other noteworthy members of this genus include L. latifolius (perennial sweet pea), L. sativus and L. chloranthus. The latter two species are primarily used in interspecific crossing of this genus to impart certain flower colors in L. odoratus.

Sweet pea has an interesting and uncertain history. The first written record of it appeared in 1695 when Fransisco Cupani, a member of the order of St. Francis, noted seeing sweet peas in Sicily. History does not record whether this sighting was made in the wild or in the botanical garden under his pastoral charge in the village of Misilmeri. It was not until 1699 that Cupani passed on the seeds of sweet pea to Dr. Casper Commelin, a botanist at the medical school in Amsterdam. Commelin published an article on sweet pea, which included the first botanical illustration. Evidently, Cupani also sent seeds of sweet pea to Dr. Robert Uveldale, a teacher and expert on new plants, in Middlesex, England about the same time. This assumption is based on a herbarium specimen collected by a Dr. Leonard Plukenet in 1700 from Dr. Uveldale’s garden.

Sweet pea’s popularity grew and with that its improvement. By the end of the 19th century, English hybridizer Henry Eckford introduced the grandifloras. This strain completely revolutionized sweet pea with its large, well-formed flowers and availability of a wide array of colors. The Spencer types, or multifloras, originated from a mutation found in 1901 by Silar Cole, head gardener of the Earl of Spencer. Today, breeding of sweet pea has focused on the development of very early flower and non-tendril types. Bodger Seed’s 'Elegance' series and 'Explorer Mix' along with Denholm Seed’s 'Snoopea Mix' are good examples of the progress in improving sweet pea made over the years.

Sweet peas can be classified in four different ways: habit, flower form, fragrance or day-length response. Plant habit can be either climbing or compact. The climbing type achieves highs of between six and ten feet; the compact between eight to 24 inches. Flower form can be single, double or semi-double. Flowers differ in fragrance so; if this is important to you, look for cultivars that are listed as fragrant. Finally, most sweet pea cultivars need lengthening days to set buds and bloom. This requirement will be achieved naturally if sweet peas are planted in the spring. Sweet peas grown in the fall in the South should be "short day" types because of the shorter days of fall and winter.

Sweet peas are cool weather plants that can take light frost without appreciable plant damage. Since they require about 50 days of temperatures under 60 degrees Fahrenheit to perform well, at our latitude they need to be started early in the growing season. Sweet peas in Missouri are best started indoors about six to eight weeks prior to planting outdoors in April. Use a welldrained, soil-less germinating medium and nick the seed coat of each seed before sowing. Sow two seeds per 3-inch (or larger) container and place in a warm location. After emergence, seedlings should be placed in a well-lit, cool location until weather allows outdoor planting. After two sets of true leaves have emerged, thin to one plant per container and space climbing types 6 inches apart, and dwarf bushy types 12 inches apart. Alternatively, sweet peas can be direct seeded into the garden in April, after the soil warms enough to support germination.

Sweet peas prefer a full- to part-sun exposure in a deep garden loam that is moisture retentive yet well drained. The latter can be facilitated through the incorporation of copious amounts of organic matter (e.g., compost, well rotted manure or peat moss) into the soil. At our latitude, a bit of afternoon shade will help to keep the plants cooler further into the growing season. Additionally, anything that can be done to keep the plant’s root system cool will help promote vigor and flowering. This can be accomplished by applying an organic mulch such as straw or dried grass clippings once the temperatures start to warm. Sweet peas should not be over-fertilized for fear of producing vigorous plants with few flowers. A pre-plant application of a garden fertilizer (e.g., 5-10-5) at the rate of one cup per 100 square feet of area should provide sufficient nutrients for the life of the plants. Good air circulation and adequate soil drainage help to prevent fungal diseases (e.g., root rot and mildew) that can affect sweet peas. Removing spent flowers from the plant will help to increase total bloom.

Container production of sweet peas is becoming popular due to the numerous dwarf cultivars now available. These petite plants are well suited for patio urns, pots, window boxes and hanging baskets. As with the production of other container-grown plants, the use of a soil-less, well aerated growing medium is recommended. A bit of support in the center of the container might be necessary depending on the cultivar being grown. U-shaped bamboo canes accommodate this task nicely. Depending upon the size of the container, direct-seed about six to eight seeds around the perimeter of the container then thin (as above) to allow three or four plants to remain. Containers can be started indoors and moved outside well ahead of the growing season since sweet peas are tolerant of light frosts.

Credit: National Garden Bureau, http://www.ngb.org/

David Trinklein University of Missouri 573-882-9631