Plants that thrive in marshy, wet areas, such as swamp rose mallow hibiscus and swamp azaleas, can also flourish in a home garden if they are watered more often than their less thirsty companions, such as hydrangea and hosta. The soil for water-loving plants should be kept consistently moist to a depth of 12 to 18 inches. Because of this need for extra water, marsh plants do better planted away from specimens that prefer drier soil.
Ruby spice (Clethra alnifolia), also called sweet pepperbush or summer sweet, is a deciduous woody shrub that grows naturally in swampy areas, along sea shores and creeks, and hillside bogs. In a home garden, this shrub can grow up to 6 feet tall and 5 feet wide. The small pink or white fragrant flowers bloom on 6-inch long panicles, or stems, in July and August followed by dark brown seed pods that remain into the winter. The attractive dark-green leaves grow to 4 inches long with fall colors in yellow and orange to golden brown. Ruby spice prefers acidic sandy soil in a partially shady location but can also be grown in full sun or full shade. The soil must be kept consistently moist. Sucker shoots that sprout up from beneath the bush should be removed immediately.
Swamp azaleas (Rhododendron viscosum), commonly called clammy or cory azaleas, grow naturally in damp wooded, swampy or boggy areas and along creeks. In the wild, they can reach a height of 15 feet and a width of 12 feet. In domestic gardens, they can grow up to 5 feet tall. The woody shrubs bloom from May to August. The trumpet-shaped white or pink flowers are 1 1/4 to 1 3/4 inches long with a distinctly clove-like fragrance. The dark shiny green oblong leaves are about 3 1/2 inches long and 1 1/2 inches wide and turn orange, maroon or red in the fall. Swamp azaleas should be planted in acidic sandy peat soil in partial shade and kept consistently moist. Rhododendron species are toxic to humans and animals when eaten.
The cardinal flower (Lobelia cardinalis) is an herbaceous perennial that grows naturally in swampy areas, along creeks, sloughs and springs. The plant base grows in a rosette with 5- to 7-inch oblong leaves that lie flat on the ground through the winter. In the spring, the plant sends up a tall spike that produces scarlet 1- to 2-inch-long flowers from July through September. The dark green stem is usually 2 to 3 feet tall but can occasionally reach 4 feet. Each plant can produce a single spike or multiple spikes. Cultivars are available with white, pink, salmon and cream flowers, and purple or reddish foliage. Cardinal flowers should be grown in organically rich soil that is kept moist. It can be grown in full sun in cooler summer climates but does best in partial shade.
- Missouri Botanical Garden: Kemper Center for Home Gardening: Clethra alnifolia ‘Ruby Spice’
- University of Texas at Austin: Lady Bird Johnson Wildflower center: Native Plant Database: Rhododendron viscosum (L.) Torr.
- Missouri Botanical Garden: Kemper Center for Home Gardening: Lobelia cardinalis
- Backyard Gardener: Clethra Alnifolia