Plants can be tested for nutritional deficiencies and diseases. Most testing done at Western Laboratories is for nutrient needs. Think of a plant test as a snap shot picture. It doesn’t tell you what has happened in the past and it doesn’t tell you what will happen in the future. If the answers are very high this may indicate herbicide damage, soil compaction, too much water, or weather conditions. If the answer is too low it could indicate the same as above plus inadequate nutrition. Once you see visual symptoms the plant has lost its vigor and you have physiologically aged the plant, possible beyond help. A perennial may gain color but it will not produce enough fruit or shade to pay for itself. Never wait for an emergency to send the patient to the hospital.