Step Two: Fertilizing
Most native and desert-adapted plants need little or no fertilizing. If plants look healthy and are growing properly, it is probably best to leave them alone.
Although uncommon for native plants, some desert-adapted plants from other parts of the world can suffer if there is a lack of nitrogen or iron availability in the soil. Deficiencies in both of these soil nutrients can cause the same effect; a yellowing of the leaves, commonly called chlorosis. If the entire leaf turns yellow, the problem is probably due to a nitrogen deficiency. If the veins of the leaf stay green, but the rest of the leaf turns yellow, it is more likely due to an iron deficiency.
It is important to note that chlorosis can also be a result of overwatering. Before adding fertilizer, check your plants and your irrigation schedule to rule out this possibility.
Nitrogen-based fertilizers and chelated iron are widely available. Because application rates and amounts vary among fertilizer types and brands, follow the instructions on the label. In general, it is best to fertilize before a plant's primary growing season (usually in the spring or summer).