Walnut Creek’s Ruth Bancroft is a national authority on drought-resistant gardening. Twice a month, she and her staff share their knowledge with readers.
While some plants have a fixed time of year when they invariably come into bloom, others are less precise. One such species is Senna artemisioides, a shrub native to Australia.
Although it generally flowers during the winter and spring months, the timing varies from plant to plant and from year to year. At the Ruth Bancroft Garden, we have had it begin as early as September and end as late as May.
Senna artemisioides is sometimes referred to as Feathery Cassia, in reference to its fine-textured feathery foliage. In older books, it is referred to as Cassia artemisioides, and the old genus name persists in its common name. In current taxonomy, most of the shrubs formerly included in Cassia have been transferred to the genus Senna, while the trees have kept the name Cassia.
The gray-green leaves of Senna artemisioides are up to 3 inches long; they are divided into very narrow leaflets that look like pine needles. On closer inspection, it can be seen that the leaf stalk and the undersides of the leaflets are silvery, contrasting with the green upper sides. The overall effect is gray-green, with the fineness of the foliage giving the plant an airy look.
This species normally attains a height of 5 to 6 feet, and sometimes a little more. At the Ruth Bancroft Garden, we value S. artemisioides for the way its feathery foliage contrasts with the solidity of large-leaved plants such as agaves and aloes.
The cupped flowers of Feathery Cassia are a half-inch to two-thirds of an inch across. They are bright yellow with a dark eye, due to the cluster of dark brown stamens nestled within the cup.
Although the flowers are not large, they are produced abundantly over a long period of time. The seed pods that follow are initially glossy green, then turn brown at maturity. They resemble narrow shiny snap peas, which is not surprising since Senna belongs to the pea family.
Sennas are found worldwide, mostly in tropical or subtropical regions. Fortunately, there are some kinds, such as S. artemisioides, with enough cold tolerance to endure the occasional dips into the 20s that we experience in Walnut Creek.
Email questions on drought-resistant plants to info@ruthbancroftgarden.org.
