When looking for an evergreen drought tolerant shrub species for the desert areas around Tucson and Green Valley, you might be wondering about the Senna species, as when it is doing well and in full bloom it can be quite attractive.
The problem with Sennas is they freeze hard below twenty degrees, despite what many reference books may tell you. This leaves you with either a totally brown plant until late spring, and of course no flowers since they bloom in late winter and early spring, or in some cases as in the hard freeze of 2010, a dead plant.
The Senna is also not very attractive after blooming, as brown seed pods persist after blooming, requiring either shearing or hand picking off to improve the appearance.
If you want to skip the high maintenance plant, try low maintenance shrubs such as the Texas Ranger, Texas Mountain Laurel, or the yellow flowered Turpentine Bush. With the Texas Ranger, make sure you are selecting a species that won’t grow out of its space.