Answer: There are a couple possibilities. First, constantly wet soil doesn't allow roots to absorb oxygen, which is essential, and yellow, browning leaves result. You didn't say how you are watering, but often times drip or other irrigation systems are not timed to run long enough to provide a slow, deep watering through the plant's entire root system. Just the top layer of soil gets moistened. This is not good because it promotes salt burn. When leaves brown around the edges, the problem is often salt burn. This is common in our area with low rainfall, alkaline soil and water high in salts. Browning usually occurs on the old leaves first. Frequent, light "sprinklings" or short time spans with drip irrigation, allow salts to accumulate in the top layers of soil, where the roots are, which is bad news. This excess salt accumulates in the leaf edges, where it kills the tissue and the leaf dries out and turns brown. It's important to water deeply, slowly and usually infrequently. Water should soak 1 foot deep for shallow-rooted plants such as perennials and cacti, 2 feet deep for shrubs and 3 feet for trees. Use a soil probe (any long, pointed piece of metal or wood to poke into the soil) to check how far water has penetrated. The probe moves easily through moist soil, but stops when it hits hard dry soil. With a young non-native tree, you should water once a week in summer, and make sure the water penetrates deep enough. At least once a month, water deeply enough to "leach" or push salts well below the root zone.
Similar symptoms occur when too much fertilizer has been applied. It's generally not advisable to fertilize landscape plants in our summer heat. Plant roots often "burn." Finally, I'm not sure what plant you are referring to as a honeysuckle tree, but gardenias, although sold here, are not at all well-suited to desert growing conditions and they will always struggle. They like moist, acidic, organic soil with humidity and don't appreciate our intense sun, heat, and drying winds. I'd recommend you choose plants that thrive in our conditions. There are hundreds of great, flowering plants. Go the following website for a free publication that provides info: http://www.amwua.org/conservation/landscape_plants.htm
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