Ask Mr. Smarty Plants

There are two members of the Senna genus native to California. One is Senna armata (Desert senna) which is native right next to Orange County (USDA Plant Profile Map) and Senna obtusifolia (Java-bean), native relatively near Orange County (USDA Plant Profile Map).

We did a lot of looking trying to find out about the senna plant, considered a subshrub. Our Native Plant Database webpages on the two native to California as well as the rest native to North America yielded very little information except that it was often considered a weedy pest. It is a member of the Fabaceae (bean) family. Here are some photos of Senna armata (Desert senna) from CalPhoto. If they are accurate, you should have a lot of flower-bearing stems instead of only one. However, two years is not a very long time for a shrub to mature.

The nearest we could find to a description of a plant is from Wikipedia:

"Senna armata is a species of flowering plant in the legume family known by the common names spiny senna and desert senna. It is native to the desert regions around the intersection of Nevada, Arizona, eastern California and northern Baja California, where it grows in sandy and rocky habitat, such as arroyos. It is a shrub growing up to a meter tall, its grooved, branching stems often narrowing to thorns at their tips. The spiny branches are coated in tubular hairs which help protect it from hot desert air. The spine-tipped leaves are each made up of two to four pairs of small leaflets. The leaves are ephemeral, dropping soon after emerging, leaving the shrub naked most of the time. Flowers occur singly or in small clusters in leaf axils. They are fragrant and showy, with five petals in shades of yellow to salmon pink, each measuring roughly a centimeter long. The fruit is a legume pod up to 4 centimeters long."

Just at a guess, with no better information, we would say your plant may simply not be mature yet. It is a desert plant, so it needs little water, no fertilizer and lots of sun. Any of those not observed, especially the fertilizer, can inhibit the blooming. One last note -almost any plant grows more quickly from root cuttings or division than from seeds.

We would suggest pruning back any dead growth or wilted flowers. Plants all need to bloom in order to reproduce theselves, so if the plant is in a good place for it to grow, it should be inspired to put on more blooms.