Answer: Fraxinus uhdei is actually evergreen to semi-evergreen, meaning that it can drop leaves but quickly leafs out again, as yours seems to be doing from your description. This usually happens because of temperature extremes or stress. "Majestic Beauty' is generally more evergreen than semi-evergreen, but we do have wild temperature extremes here, which is stressful. As for the leaves turning brown, that may be an indication of ineffective watering. Frequent irrigation, such as twice a week, can contribute to salt burn and leaf drop. I'll include some info below about effective watering for our local conditions.
Here are some watering guidelines from Desert Landscaping for Beginners, published by Arizona Master Gardener Press. Days between watering for established high-water-use (i.e., non-native) trees: March-May, 7-12; May-October, 7-14; October-December, 7-12; December-March, 14-30.
Often times with irrigation systems, they are not timed to run long enough to provide a slow, deep watering. When leaves start to 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. 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 infrequently as possible. Frequent, light "sprinklings" or short time spans with drip or bubbler irrigation, allow salts to accumulate in the top layers of soil, where the roots are, which is bad news.
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."
Use the 1-2-3 Rule as an easy method to remember how much water to apply. Small plants with shallow root systems, such as perennials, veggies, herbs, cacti, succulents have roots that reach about 1 foot deep, so water needs to penetrate that far. When the top 1 inch of soil dries out, it's usually time to water again. Shrubs have root systems that are 2 feet deep so water needs to soak 2 feet deep. When the top 2 inches of soil dries out, it's time to water. Trees are 3 feet, etc. As plants establish root systems, the time between waterings can be lengthened, but it is always essential to water to the same depth. So you are applying the same amount of water with each irrigation regardless of the time of year, but the frequency changes. As warm weather arrives, you need to water more frequently than during winter. For veggies and small plants, it may be necessary to water daily. A soil probe will help you determine how far water has soaked. It moves easily through wet soil but stops when it hits hard soil. I?d suggest you let your system run for 30 minutes, then wait an hour or so (for the water to continue penetrating), then use a sharp stick or pointy thing as a soil probe to determine how far the water penetrated in your soil. Keep adding increments of 30 minutes until it reaches the 3 foot depth. For most areas, it's necessary to run irrigation much longer than people would think. The majority of the plant problems we see are because water is running too frequently, and not enough is applied.
I hope this information helps!
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