Phosphorus is an important nutrient in all plants as it is required for membranes, energy molecules and nucleic acids. However, it is seldom deficient in stone fruit trees in California. We have been able to induce deficiency in trees planted in large tanks filled with clean sand (see photos at right), but have never documented the disorder in commercial orchards. Also, we have never been able to show any benefit from adding P containing fertilizers to mature orchards or newly planted trees. Leaf samples collected in mid summer should have P values between 0.1 and 0.3% (survey). If values drop below 0.12%, the trees might benefit from the addition of a soil-applied triple (NPK) fertilizer.