The Q&A Archives: Leaf Yellowing On Fruit Trees, Strawberries, Grapes And Red Tip Photinia.

Question: We live in the Southwest desert of Az. We have planted apple trees, strawberries, grapes and red tip photinia. The new growth leaves are yellowing with green vains showing. We fertilized after symptons first started, with miracle grow @ followed up 1 month later with slow release fertilizer. We water by drip system, giving each plant approximately 6-7 gallons of water per week (2 gallons every other day). We have mulched some of the plants and have not mulched others. We've tried cutting back on water, but then the plants seem to want to die.

Answer: Iron chlorosis is a common occurence in the desert. This iron deficiency is recognized by new leaves that are yellow, while the veins remain green. If the condition is severe, the entire leaf may be yellow. Non-native plants are likely to suffer from it, while native and desert-adapted plants weldom do. The plants you mentioned are of course all non-native.
Although iron may be present in the soil, it is not always in a form that plants can use. Overly wet soils (during the rainy season, for example) are depleted of oxygen. (As water fills in the minute spaces between soil particles, air moves out.) Plant roots need oxygen to absorb iron in the soil. To help prevent chlorosis, always water slowly, deeply and infrequently. (More on correct watering practices for the desert below.)
Soil with a high pH (alkalinity) also inhibits iron absorption. Our soils are highly alkaline at 8.0 to 8.5. If you are using correct irrigation methods and symptoms are still present, apply iron chelates or ferrous sulphate to the soil. Both are readily absorbed by a plant?s roots.

Desert soil and water both contain salts, which can accumulate in the root zone over time. This salt buildup forms where the water stops penetrating. If you ?sprinkle? plants lightly and frequently, or don't allow drip systems to run long enough to soak the root zone, salts will build up in the top layers of soil and damage or kill your plant. Deep watering?or leaching?prevents this by flushing the salts past the root zone.

Roots also need oxygen to survive and soil that is continually wet doesn?t provide it. 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. For trees, water should reach about 2-3 feet deep. For shrubs, 2 feet, annuals and perennials, 1 foot. There are numerous variables involved for watering schedules, such as type of soil, how fast or slow it drains, sun and wind exposure at your site, temperature, age and condition of the plants and much more. It?s important to learn the specific needs of your landscape, both for its health and your water bill. Use the information above to determine how moist the soil is before automatically applying more water. I hope this info helps!

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