No single symptom tells you that trees or shrubs need additional fertilization. Some nutrient deficiency symptoms can be similar to symptoms of cultural problems or diseases. Slow growth rate, small leaves, fewer flowers, smaller fruit, and pale green or yellow (chlorotic) foliage with mottling between the leaf veins may all be signs of nutrient deficiency.
Two methods of determining nutrient deficiencies include:
Advantages – provides soil pH, levels of K, P, organic matter content and minor nutrients such as iron or zinc.
Disadvantage – does not provide reliable information on N because N is rapidly lost through leaching or removed by plants
There are two methods of determining nutrient deficiencies through plant analysis:
Visual symptoms – include length of shoot growth, leaf color, leaf size, and color pattern and timing of leaf drop
Advantages – N and Fe are often the easiest visual symptoms to identify
Disadvantage- symptoms can be deceiving and/or nonspecific
Foliar tissue analysis – provides the concentrations of specific elements in plant foliage (usually leaves)
Advantages – when combined with soil tests it can provide a good picture of nutrient problem(s) – deficiency or toxicity
Disadvantage- nutritional needs for many landscape plants is unknown