Sweet peas are popular garden plants because of their large, fragrant flowers colored pink, red, blue, purple, orange or white. Sweet peas grow as vines or as bushes and prefer cooler climates. While most sweet pea plants are annuals, there are a few perennial types available. Perennial sweet peas tend to be hardy and are able to adapt to a range of conditions.
Lathyrus latifolius, the perennial sweet pea or everlasting pea, is the most common perennial sweet pea and can be easily found at most garden centers. Blossoms are white, pink and pale purple, grow on vines and, unlike annual varieties, do not produce fragrance. Like all sweet peas, it prefers colder climates and will thrive up to USDA Zone 3. The everlasting pea needs full sun to grow--plants grown in the shade will not produce blossoms--and will tolerate a dry soil. Plants grown in clay soils tend to rot over the winter. The plant self-sows very well and will spread out of control if not pruned back. To care for an everlasting pea plant, prune it back to ground level in the fall.
Lathyrus palustris, also known as the marsh pea or marsh vetch, grows in warmer climates than the everlasting pea and, according to Caroline A. Creevey, author of the "Harper's Guide to Wild Flowers," tends to be found from New Jersey southward. The marsh pea--named because it is commonly found in boggy areas --produces delicate blue flowers and grows on vines 1 to 3 feet long. Marsh pea seeds must often be special ordered, as they are difficult to find at gardening centers.
Lathyrus vernun, also called spring vetch, grows as a small shrub about 2 feet in height. Typical of sweet pea plants, it is found in northern regions, generally north of Virginia in the U.S. In the wild, spring vetch can be found in meadows, fields and deserted lots. Spring vetch has large, pale purple flowers. Used in gardens, spring vetch works well as a border plant, and seeds may be available from garden centers and nurseries. Other colors, especially red and white, are also available as special cultivars.
Lathyrus sylvestris, or the flat pea, grows as a vine and produces pink or purple flowers. According to the U.S. Department of Agriculture, the flat pea is a wetland indicator and, while it is found throughout the U.S. and Canada, it is most common in northern regions. Blooming in early summer, the flat pea is a suitable garden plant with some tolerance for shade.