Culture
Easily grown in wet soils in full sun to part shade. This plant is a native U.S. wetland plant that thrives in marshes, bogs, and the mucky banks of ponds, lakes and water bodies, including locations in shallow standing water to 24” deep in the eastern half of North America. It often colonizes in damp ground near shorelines. This plant can spread rapidly. It is considered to be an emergent aquatic plant in stagnant, slow-moving water. Plants will clonally reproduce whenever the stem tips dip to touch moist ground or water.
Noteworthy Characteristics
Decodon vertilicillatus, commonly known as swamp loosestrife or water willow, is a multi-stemmed, woody-based, sub-shrub that typically grows to 6-8’ tall in a variety of wetland areas ranging from swamps to areas where plants are partially submerged in standing water to as much as 24” deep. It is native to marshes, water margins, peaty bogs, sloughs, swamps and shorelines along ponds, small lakes and fens, from Ontario and central Maine south to Florida and Louisiana north along the Mississippi River to the Missouri bootheel and southern Illinois.
Slender, recurved to arching, usually unbranched, wand-like stems grow to 3-8’ long. Stems of plants growing in water margins will typically arch over the water in an ornamentally attractive fashion. Stems are clad with toothless, nearly stalkless, elliptic-lanceolate to lanceolate, opposite or whorled, willow-like leaves (each to 1 1/2 to 6” long and to 1” wide). Showy, bell-shaped, five-petaled, deep pink to rose-purple flowers (1” across) bloom in dense clusters in the upper leaf axils during July-August. Each flower has five petals, 5-7 sepals and 10 stamens. Fruit is a rounded capsule. Plants may form sizeable clumps at the edges of lakes and streams. Leaves acquire often attractive shades of red, orange and yellow in fall. Despite the willow-like leaves, this plant is not related to willows.
D. verticillatus is the only species in this loosestrife family genus.
Genus name is from Greek decas meaning odous meaning teeth in reference to the calyx having 10 teeth.
Specific epithet means having whorls in reference to whorled stem leaves.
Problems
No serious insect or disease problems. Japanese beetles can be problematic in some areas.
Uses
Moist to wet soils in sun. Not a good plant selection for small gardens. It is useful as a waterside plant in large landscapes. Willow-like leaves arch gracefully over water margins. Hedge. Single specimen.