Answer: Gardenias are not well-adapted for Arizona, as they prefer acidic soil and more humid conditions. Our soil is highly alkaline and of course, we are hot and dry. I would guess that your original gardenia was not being watered deeply enough, but may have been watered too frequently. Always water slowly and deeply and as infrequently as possible. Our water and soil contain lots of salts, and deep watering is essential to leach the salts beyond the root zone. Short periods of watering are harmful, as the roots don't get the water and salts will accumulate in the top layers of soil, causing salt burn. Salt burn shows up as yellowing along the leaf margin, eventually the entire leaf will brown, and in severe cases the plant will die. Non-natives, such as gardenia, are susceptible to salt burn. To answer your question about watering, use the 1-2-3 Rule. Water should soak 1 foot deep for annuals, perennials, cacti and succulents, groundcovers and other shallow-roooted plants; 2 feet deep for shrubs (like your gardenia) and 3 feet deep for trees. Use a soil probe to determine how far water penetrates. Any long pointed piece of metal or wood, if your soil isn't too hard. The probe will move easily through moist soil but will stop at dry, hard soil. Let the top 2 inches of soil dry out before applying more water. You may have to dig below the mulch and poke your finger in the soil until you get a feel for how long moisture stays in your soil. Mulch is excellent for retaining soil moisture and reducing soil temperatures, so I'd recommend continue using it. Hope this info helps!
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