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Photo by Ayinde Listhrop

Plant of the Week: Wild Senna

By Matt Vermeulen | September 5, 2017

Wild senna, this week’s plant, is a new addition to the High Line and blooming for the first time this summer. (Look for it in the Chelsea Grasslands section of the High Line, between 17th St. and 20th St.) Also known as Senna marilandica, it is a shrubby, herbaceous perennial native to the East Coast through the Midwest and down to Texas. When mature it can reach heights of 4-6′. Senna marilandica was formerly known as Cassia marilandica and may still be sold under that name.

Senna marilandica has alternate, compound leaves and a showy cluster of bright yellow flowers. After the flowers are pollinated, they form 4″ long seedpods that eventually turn black and persist on the plant after the leaves have fallen. Wild senna needs full sun and will thrive in well-drained soil. It needs a medium amount of moisture, so be sure to water it in warm weather. Once it is established, it should become more drought tolerant. Wild senna can provide excellent forage for a wide number of species, and attracts pollinators. It is a host plant for several caterpillar species, including Cloudless Sulphur, Little Yellow and Sleepy Orange butterflies.

The pea-like seedpods immediately mark Wild senna as a legume—a member of the fabacae, or bean family. (Faba means “bean” in Latin.) Fabaceae is one of the largest plant families, with over 19,000 species ranging from tall, tropical trees to tiny annuals. Most members are herbaceous perennials like our Wild senna. In addition to being widely distributed around the globe, this family also has major importance as a food crop. Its members include chickpeas, alfalfa, peanuts, peas, and of course beans. Many members of this family also work to “fix” the soil by adding nitrogen, which plants need to grow.

Wild senna may be affected by particularly cold winters, so if you live in a potentially harsh climate, mulch around the plant in fall to give it a better chance to survive. It does not have major pest issues, but could attract slugs. Senna has the potential to be weedy if allowed to self-seed, so collect the seedpods before they burst open to control the spread of the plant. It could be an interesting accent plant in a native garden.

In the Chelsea Grasslands, between 17th and 20th streets.

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.

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