Wild Senna Beats the Heat

This tall yellow wildflower loves the heat and seems to laugh at drought. Five or six feet tall on sturdy stems, Wild Senna (Senna hebecarpa) has typical pinnate Pea Family foliage but the individual flowers are more open than typical in the family. Wild Senna belongs to an early-evolved branch of the Pea family tree. The open flowers are very appealing to large bumble bees. 

We have also seen hummingbirds visiting the Wild Senna flowers this year. Our hummers are foraging hard this season because so many of our cardinal flowers, the hummingbird favourite, died in the drought, and the wild Spotted Jewelweed along the seasonal stream is a fraction of its usual self.

Wild Senna does not occur in the wild in the Ottawa Valley — it hails from a little further south and occurs in southern Ontario south of Brantford. A lovely yellow butterfly whose caterpillars rely on Wild Senna — the Cloudless Sulphur — also occurs south of here. Wild Senna is an acceptable host plant for some other butterflies, including the Silver Spotted Skipper, that eat a diversity of native plants in the Pea Family, We have an abundance of Silver Spotted Skippers because we have a lot of their main host plant, Black Locust. I would never recommend planting Black Locust, which is an extremely aggressive suckering tree and thorny as all out. We are trying to beat back our Black Locusts. It is nice to know that if we ever succeed in eradicating the Black Locust (not too likely) we can still provide for the Silver Spotter Skippers with a handsome and well-behaved herbaceous flower, the Wild Senna.

Plant Wild Senna at the back of a sunny border. After the flowers finish. thin black pods remain decorative through the autumn. This plant does not need staking, fertilizing, or dividing. It consorts beautifully with tall ornamental grasses.