PREFERRED SOIL pH: Near neutral
PREFERRED SOIL TYPE: Fertile, moist
PREFERRED LIGHT: Sun to partial shade
ATTRIBUTES: Delicate foliage; dainty, fragrant flowers; for trellises, cut flowers
SEASON OF INTEREST: Spring to summer
TYPE OF VINE: Tender annual; climbs by clinging with tendrils
FAVORITES: 'Winter Elegance' for hot climates; Old Spice hybrids for fragrance
QUIRKS: Sweet peas expire in hot weather and foil to thrive in dry soil
GOOD NEIGHBORS: Lobelia, pansies, or sweet alyssum
WHERE IT GROWS BEST: Areas with mild winters, cool springs, or consistently cool summer nights
POTENTIAL PROBLEMS: Heat stress, aphids
RENEWING PLANTS: Reseed each year
CRITTER RESISTANCE: Poor; shoots vulnerable to deer, rabbits, and woodchucks
DIMENSIONS: Annual 4-6 ft (1.2-1.8 m); perennial 10 ft (3 m)
Sweet Pea in the Landscape
Popular for centuries as fragrant cut flowers as well as sumptuous garden vines, sweet pea vines bear elegant pocket book-shaped blossoms in colors including white, yellow, pink, red, purple, and blue, and bicolors. Old-fashioned types, such as Old Spice hybrids, have the headiest perfume but usually fewer and smaller blossoms. Modern types boast long wands of fluttery flowers in luminous shades but aren't as aromatic as old varieties. Most grow 4-6 ft (1.2-1.8 m) tall and usually have stiff, upright stems if given the support of a string or net trellis. There are also bush varieties sufficiently compact to use at the garden's edge or in containers.
Sweet peas require cool weather, and young plants are surprisingly hardy. In Zones 7 to 9, especially hardy varieties, such as 'Winter Elegance' are sown in winter for flowers first thing in spring. Where winters are more severe, spring-sown sweet peas can be used as a backdrop for other cool-season spring flowers, such as pansies and snapdragons.
All in the Family
While regular sweet peas grow and flower poorly in hot weather, the perennial pea (Lathyrus latifolius) can take the heat. This vigorous vine, which grows to 10 ft (3 m), produces pink or white blossoms that resemble sweet peas but do not have their scent. Perennial sweet peas are dependably hardy to Zone 5 and flower through the hottest summers.
Growing Sweet Pea
Soak seeds overnight in water and plant them 2 in (5.1 cm) deep in cool garden soil that has been deeply dug and amended with organic matter, such as compost. Time planting to take advantage of cool weather. Plant in midwinter in Zones 8 and 9, in late winter in Zones 6 and 7, and as soon as the soil can be worked in cooler regions. Cold-climate gardeners can also jump-start the season by sowing seeds indoors in late winter, using individual peat pots. Keep the soil barely moist and grow the seedlings on a sunny, cool window-sill. Transplant them into the garden 2 weeks before your last frost date. Handle seedlings gently, planting peat pot and all, and disturb the roots as little as possible.
Mulch the soil around the roots with a 3 in (7.6 cm) thick layer of chopped dried leaves, straw, or shredded bark to keep the roots cool and moist. Install a trellis early on and help the young plants find the support if their own search falters.
Pick off spent flowers to encourage continued flowering. If you see the small, pear-shaped, sap-sucking insects known as aphids clustered on the leaf undersides of new growth, knock them off the plant with a forceful spray of water. Or apply insecticidal soap according to the package directions. Four-footed pests, including deer, rabbits, and woodchucks, nibble sweet peas. Fencing them is the best defense, but applications of a commercial repellent used as directed on the label is somewhat effective.