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Plant of the Week: Swamp-Rose Mallow

By Isabella Yeager | July 13, 2015

The High Line’s planting design is inspired by the self-seeded landscape that grew up between rail tracks after the trains stopped running in the 1980s. Today, the High Line includes more than 300 species of perennials, grasses, shrubs, and trees – each chosen for their hardiness, adaptability, diversity, and seasonal variation in color and texture. Some of the species that originally grew on the High Line’s rail bed are reflected in the park landscape today. This week we share one of our gardeners’ current favorites with you.

Aloft on stems up to seven feet tall, the bubblegum-pink blooms of the swamp-rose mallow are impossible to miss when woven as they are on the High Line between the tall, narrow cattails. Hibiscus moscheutos has lush, smooth green foliage and saucer-sized flowers that are a welcome sight in the heat of summer. While each bloom lasts only one day, flowering time extends throughout the season. Up close, you’ll find up to 13 light-yellow stamens and a delicate petal venation that gives the blooms an almost ruffled look. Even the buds are striking, coming to velvety, sea-green points. About one month after flowering, seed capsules mature and turn brown. As they dehisce, seeds scatter and take easily in good conditions, and stems maintain beautiful upright structure and dramatic seed heads that provide atmospheric winter interest.

Lady Jean Skipwith, a contemporary and friend of the great botanical recordkeeper Thomas Jefferson, wrote of her cultivation of the swamp-rose mallow, which would have grown in the swampy areas of Southern Virginia where Skipwith lived and practiced horticulture. To this day, the swamp-rose mallow can be found along the banks of brackish and salt marshes and wetlands, preferring consistently moist soil and partial-to-full sun. Its territory extends from Texas throughout the Southeast United States and North to Ontario. A confection made since ancient times from the boiled roots of its cousin Althaea officinalis in Europe and Northern Africa has evolved into our modern marshmallow.

An attractive habitat element for pollinators, the swamp-rose mallow has its very own specialized bee species, the rose mallow bee. The large, bell-like flowers act as a backdrop for many of the bees’ behaviors, including the romantic and competitive aspects of mating. Male bees fly from flower to flower looking for females, and spar with each other inside the blooms when challenged. The swamp-rose mallow is a protected species in many regions because of its historicity as an American species and its importance to the rose mallow bee, which pollinates no other plant. Taking this into account, it’s best to check USDA resources before digging it up or gathering its seeds.

Because the flowers are borne apically, as opposed to other varieties of hibiscus that carry buds along the stem, the swamp-rose mallow can be a bit top-heavy. It works well when grown among, for example, the structurally supportive cattails and reeds of its natural habitat. Staking may be necessary if the plant is grown alone.

Garden varieties can be grown as half-hardy annuals, blooming in 4-5 months when started from seed. Can be treated as a perennial, overwintering easily with good drainage and the root crown protected with a mulch layer. Rich soil in early summer will provide support for its rapid growth.

Diller von Furstenburg Sundeck & Water Feature

Our horticultural team counts on members and friends like you to help keep the High Line beautiful and thriving. Join our community of supporters who play an essential role in the High Line’s most important gardening projects – become a member of the High Line today!