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.
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.
WHERE TO FIND THIS PLANT:
In the Chelsea Grasslands, between 17th and 20th streets.
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