Many farmers use leaf and soil analysis to help diagnose problems and apply fertilizers efficiently. From time to time gardeners may also benefit by taking a soil or leaf sample to a laboratory for analysis. In particular, tests which shows the levels of certain minerals (both deficient and toxic levels) can be very useful in helping to determine why plants may be growing poorly.

When plants grow poorly, a mineral deficiency or excess may be responsible. However, plant symptoms such as stunted growth, abnormal leaf color, poor fruit production, leaf burn or leaf drop, and twig dieback are more often caused by other factors. For instance, plants will be stunted if they do not receive adequate water; the margins of their leaves may also burn, especially during hot weather. Too much or too little of certain elements will cause the same symptoms.

Waterlogged soils often have little oxygen in them because excess water fills all the spaces between the soil particles. Plants growing in waterlogged soils often develop small, yellow leaves, and twig and branch dieback. These symptoms are often mistaken for iron and other micronutrient deficiencies. Under such conditions the plants may respond, at least temporarily, to applications of micronutrient fertilizers. However, proper watering techniques would provide more effective results.

Unfavorable climatic conditions, insect pests, diseases and misapplied pesticides may also produce symptoms that resemble nutrient deficiencies. For instance, insects called thrips often cause stunting and distortion of foliage by feeding on new spring growth.

Certain root diseases may cause yellowing of foliage which can resemble nutrient deficiencies. And certain herbicides (weed killers), when improperly used, produce symptoms on plants that could be confused with symptoms of zinc or iron deficiencies.

If you have a sick plant, first check to make sure that the growing conditions are correct for that species. For instance, are you trying to grow a shade-loving plant in full sun? Or, are you trying to grow a species totally unadaptable to the Central Valley's hot, dry summers. Is the soil compacted, preventing water penetration? Check your cultural practices by digging a hole to see how wet or dry the soil may be. Are you trying to grow so-called "acid loving plants" (like azaleas, gardenias and camellias) in an alkaline or high pH soil? If so, the plants will constantly appear iron deficient. Also, carefully check your plant for insect pests and diseases. With smaller plants, such as vegetable or bedding plants, pull up a plant or two and check to see if the roots are healthy. Plants being attacked by root-feeding nematodes have symptoms (stunted growth, small, yellow leaves) that may resemble certain nutrient deficiencies.

If you have considered all of the obvious possibilities and still can't find a clue to your problem, a soil or plant tissue analysis may be very appropriate. Commercial soil testing laboratories provide the most complete and accurate analyses. Many labs also provide recommendations based on the test results. It's a good idea to call the lab and ask for advice before sending or taking in a soil or plant sample.