Biennial plants are those that complete their life cycles in two years. Under normal conditions, according to the Oregon State University Extension, these plants spend their first year developing leaves and the structures to store food. After resting during the winter, they flower, fruit and set seed in their second year before dying. Faced with temperature extremes or prolonged drought, some biennials might "bolt" and compress their entire life cycle into a single year.
Common foxglove ( Digitalis purpurea) is a favorite garden biennial native to Europe. Hardy to minus 30 degrees Fahrenheit, foxglove grows up to 5 feet high and 30 inches wide. During its first year, the plant produces a basal clump of oblong, pale green leaves. In late spring of its second year, one-sided spikes of white, deep pink or purple 2-to-3-inch, funnel-shaped flowers rise on leafy stems from its base. Each bloom has white and purple interior markings. Hummingbirds flock to foxgloves.
Use foxglove, recommends the Missouri Botanical Garden, at the back of a perennial border. Placed in front of dark-leave shrubs, its blooms are even more eye-catching. Common foxglove prefers partial shade and consistently moist, fertile, well-drained, acidic (pH below 7.0) soil. It's susceptible to powdery mildew, leaf spot, aphids and mealybugs. Allow foxglove to release seed for a new crop of plants the following spring.
Money plant (Lunaria annua) is a spring-blooming biennial native to central and southern Europe. Reaching up to 3 feet high and 2 feet wide, it has hairy stems with serrated, heart-shaped, medium green leaves. Money plant is hardy to minus 20 degrees. In April and May of its second year, according to the Missouri Botanical Garden, clusters of four-petaled, half-inch purple flowers appear on stems above the foliage. Flat, 2-inch, green, papery fruit that takes on a silver translucence as it ages follows the flowers. Dried stems of fruit are attractive in floral designs. Use this insect- and disease-resistant biennial in borders or shade gardens. It likes full sun or partial shade and rich, moist soil. Plants self-sow readily.
Evening primrose (Oenothera biennis) is another hairy-stemmed biennial reaching from 2-to-6 feet high. It grows wild in woods, long lake shores and on dry plains across much of the United States. In its first year, evening primrose produces a rosette of lance-like, medium green leaves. The next spring, it has leafy, branching stems bearing dense spikes of deep yellow, 2-inch blooms. The fragrant, hummingbird-attracting flowers open at night and close by noon. Evening primrose, according to the Lady Bird Johnson Wildflower Center, grows in full sun to shade and dry, sandy or rocky soil.