Answer: Feathery senna is evergreen and cold-hardy to 20 degrees. Did your winter temperatures drop below that? What about soil moisture? When desert plants are stressed for water, a natural reaction is to drop their foliage to survive. When you water, make sure it penetrates to a depth of 2 feet, and apply it at the outer edges of the plant canopy, where feeder roots absorb water and nutrients. Use a soil probe to help determine how often to apply water. Poke it into the soil. It will move easily through moist soil and stop at dry soil. Nor should soil be saturated as roots need oxygen or they will rot. Finally, scratch some of the stems lightly with your fingernail. Live tissue will show as green, meaning that your shrub is still alive and should leaf out.
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