Gooseneck loosestrife (Lysimachia clethroides), an upright, clump-forming perennial, grows to a mature height of 2 to 3 feet, with slender, arching white flowers that resemble the neck of a goose from a distance. The plant is fairly easy to care for, though it can grow aggressively through underground rhizomes to form a dense colony in the garden.
A native of China and Japan, gooseneck loosestrife prefers the temperate conditions of U.S. Department of Agriculture plant hardiness zones 3 through 8. The plant will grow in full sun or partial shade. The Missouri Botanical Garden notes it generally grows less aggressively if planted in dry soil with light shade. Growing it near a shed, fence or other sturdy barrier will help keep the fast-growing plant from spreading out of bounds.
The adaptable perennial is not picky about soil, growing in poorly draining, chalky or clay soils and well-draining sandy soils. It will look its best in a moist soil enhanced generously with humus. To help keep the plant looking tidy, cut back after flowering. Gooseneck loosestrife is susceptible to slugs and snails, which chew holes in the plant's pointed green foliage. Pick slugs and snails off the plant by hand in the evening, when they are most active, and drown them or crush them.
Gooseneck loosestrife produces rich gold fall foliage and long-lasting flowers that will continue from summer until fall. The flowers work well for fresh cut flower arrangements. The plant is rarely bothered by diseases or pests, such as rabbits, though it may get rust or leaf spot if you water it from overhead. Gooseneck loosestrife can be used to lend a naturalizing effect to a cottage or woodland garden or to add texture and interest to the moist soil near a stream or pond.
Gooseneck loosestrife generally self-sows freely, often to the point of becoming a nuisance. It is easily propagated from seeds, sown in fall in a cold frame and moved into individual pots until summer. The plant may also be propagated by division in spring or summer. Plants for a Future recommends planting larger divisions directly in their permanent positions and planting smaller divisions in pots in a cold frame until they've developed a strong root system.