Answer: It sounds as if you are doing most of the correct things to get gardenias to grow in the desert. (It's not their favorite place, as you probably know!) And, I'm glad to hear you have worms in your soil--it means you must have a good supply of organic matter. I assume that when you flood water, you're giving them a good soaking that would leach any salts below the root zone. You didn't say how old these plants are. Yellow leaves can be a sign of several things, including transplant shock for new plants; lack of nitrogen; or inability to absorb iron from the soil. If the new leaves are green, and the old leaves are yellow, it's probably a nitrogen deficiency. (Feed with a balanced fertilizer such as 10-10-10, or an organic fertilizer such as fish emulsion.) If new leaves are yellow, with veins showing green, the plant may be having difficulty absorbing iron from our alkaline soils. Apply a chelated iron source. Finally, gardenias do prefer a more acid soil, and as you probably know, our soils are in the 8 to 8.5 range. Even in improved beds, the soil tends to be alkaline. Add peat moss, pine needles (if you can find them), or gypsum to your soil to help reduce alkalinity. Good luck, and feel free to write again if these methods don't seem to work.
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