Plant of the Week: Swamp Azalea

There are two Rhododendron species represented in the High Line collection, both located in the Flyover woodland garden. The swamp azalea, Rhododendron viscosum, is in full, fragrant bloom. It is an openly branched shrub that grows up to 12 feet tall, but on average maxes at 5 feet. The leaves are on the ends of the branches, measuring between 1 ½ and 3 ½ inches long and ½ to 1 ½ inches wide, and are often shiny and green on both sides. Swamp azalea can be found in wet lowlands, bogs, swamps, and stream edges from southern Maine to northeastern Ohio, south to Florida, Alabama, and Louisiana.

It is a highly variable species, one of 17 native species to the United States. The species name now includes two other forms that were once considered distinct species: Rhododendron serrulatum and Rhododendron oblongifolium. The flowers are highly fragrant, reminiscent of cloves and bay rum, and are tubular, white with a lavender purple-colored tube at the base, about 1 ¼ to 1 ½ inches in length with five spreading, petal-like lobes. Swamp azaleas typically bloom in the New York City region between May and July.

Photo by Ayinde Listhrop.

All parts of rhododendrons are considered toxic for consumption, including the honey derived from the nectar of its flowers. They contain a chemical compound called grayanotoxin, found in many other members of the Ericaceae family, which can cause body paralysis, breathing difficulties, and cardiac arrest. European honey bees that forage in areas with large populations of Rhododendron species can produce a lethal honey known as "mad honey" which has been used historically for folk medicinal and recreational purposes.

Photo by Ayinde Listhrop.

Rhododendron viscosum appreciates moist, acidic soils with high organic content. It thrives in part shade, is flood tolerant, and is suitable for heavier, clayish soils. It performs best in US Hardiness Zones 4 through 9, and appreciates a good mulching with leaf mold, shredded bark, pine needles, or wood chips in the spring. It is one of the latest blooming native azaleas, so plant with earlier blooming species, such as dwarf azalea, Rhododendron atlanticum (the other Rhododendron species found on the High Line), to extend the bloom season in the garden

Rhododendron viscosum can be found growing in the Philip A. & Lisa Maria Falcone Flyover, from 26th Street to 28th Street.

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 500 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. Every week we share one of our gardeners' current favorites with you.

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.

TD Bank is the Presenting Green Sponsor of the High Line.

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