When selecting native plants for the garden, seashore or saltmarsh mallow is often overlooked in favor of its larger-flowered cousin, Hibiscus. While seashore mallow might not have the huge flowers of its well-known relative, its flowers are by no means modest or less showy. Additionally, its hairy leaves offer resistance to sawfly larvae, which can defoliate the smoother-leaved Hibiscus.
In the wild, seashore mallow is native along the coast from Long Island south to Florida and into Texas. It is confined to brackish and freshwater tidal marshes, where it can sometimes be found growing in large stands. Despite its coastal origins, seashore mallow can be successfully grown in gardens far from the beach and is hardy to USDA hardiness zone 6 (average minimum temperature of -10°F). Also, plants don’t need to grow in marshes to thrive and can be cultivated in a wide variety of soils as long as they do not dry out while the plant is in flower.
Seashore Mallow could be described as a shrub that dies down in the winter. In late spring growth emerges from a woody, clump-forming rootstock and quickly reaches five feet in height and width, so give plants plenty of room when deciding where to place them. Siting plants in a sheltered and sunny spot will prevent the need to stake and ensure there are plenty of flowers.
In garden literature, seashore mallow is often described as a relatively short-lived perennial, persisting five years or less. Whether these reports are caused by cultural conditions or genetics of the plant material is uncertain, but in our garden, we have 15-year-old plants that are thriving and show no sign of decline.
Seashore mallow bears two to three inches in diameter blossoms that are typically rosy-pink in color, though there is a white-flowered variety called 'Immaculate' in cultivation. Flowering usually begins in July and it is not uncommon to have flowers still opening in October. Like okra, cotton and some other members of the mallow family, the flowers open early in the morning and wilt in the afternoon, unless the sky is overcast. Though each flower opens for only one day, the blossoms are borne in such profusion that mature plants can have dozens of flowers open each day during their flowering season. Seashore mallow blossoms are self-pollinating and don’t require a pollinator to fertilize the seeds, but this doesn’t stop pollinators flocking to the flowers to gather nectar.
In the landscape, seashore mallow has traditionally been used for ecological restoration where it is perfect for planting around ponds and lakes, in ditches, rain gardens, and brackish marshes. In the garden, it can create a strong texture element and can be used successfully as a focal point in all but the smallest gardens. Below are some native plant companions that enjoy similar cultural conditions and provide textural contrast to the coarser leaves of seashore mallow:
- Switch Grass (Panicum virgatum)
- Purple Milkweed (Asclepias purpurascens)
- Blue Flag Iris (Iris virginica)
- Virginia Chain Fern (Woodwardia virginica) - best used in large gardens where it has plenty of room to spread
- Ironweed (Vernonia spp.)
- Joe Pye Weed (Eutrochium spp. - formerly Eupatorium)
Not only does seashore mallow make a great garden plant, it is also being trialed by the University of Delaware as an agriculture crop that doesn’t need to be replanted every year and can be irrigated with brackish water. The most important part of the plant is the seeds, which have a high oil content, but fibers from the stems also have the potential for a variety of uses.
Propagation is straight forward. Seeds germinate quickly without any pretreatment as long as the temperature is above 75°F. Seedlings grow quickly, especially during the warmer months of summer, and can flower in the first year. In ideal conditions, plants self-seed under the parent plant, but they are rarely a nuisance. Care should be taken when collecting seeds and wearing gloves is highly recommended. The seeds pods are covered in small hairs that can sometimes pierce the skin, very similar to slivers of fiberglass.
Tip cuttings taken before flowering will root in less than three weeks and can be potted up to plant in the garden in the fall. When potting up cuttings, make sure to bury at least one node (where stem and leaf join) below the soil surface to allow for additional growing points; this is so plants will successfully break dormancy in the spring.
Not too long ago, seashore mallow was assigned a new botanical name. The reason for the name change goes back to when America was colonized and some seeds unknowingly made it back to Europe, probably in the ballast of a ship. Over the years, they spread and naturalized along the Mediterranean coast. This plant was thought to be native to that area and was named Kosteletzkya pentacarpos before the plants in America were named Kosteletzkya virginica. This was fine until it was discovered that the Eurasian plants originated in America and were actually the same species. And because the Eurasian plant was named first, Kosteletzkya pentacarpos is now the correct name to use. The joys of nomenclature!
Looking to buy seashore mallow plants? We have them for sale right here on our website.