Nutrient Deficiencies
Click for larger image Possible nutrient deficiency on sweet potato vine (Ipomoea)

Most plants growing in average garden soil in the St. Louis area receive sufficient nutrients from the soil that deficiencies are not a problem. The most notable exception is iron chlorosis of trees and shrubs, which is more likely to result from a high soil pH than a lack of iron in the soil. See below for more information on this deficiency. Also, because of the higher nitrogen requirement of turf grasses and leafy vegetables in the vegetable garden they may benefit from some additional nitrogen fertilizer. Also, nutrient deficiencies are likely to occur in plants growing in containers that are not fertilized regularly because of the reduced soil volume and the lower nutrient holding capacity of soil-less mixes used for container plants. Following is some brief information on the symptoms of common nutrient deficiencies:

Macronutrients

Nitrogen

Lack of nitrogen shows up as overall yellow-green leaves instead of a dark green, yellowing and dropping of lower leaves (can be caused by many factors), and overall reduced plant size and slow growth. Although most garden plants receive adequate nitrogen from the soil and dissolved in rainwater, applying nitrogen in a complete, balanced fertilizer such as 20-20-20 once a year around perennials and shrubs is usually sufficient to provide adequate growth. Leafy vegetables can benefit from additional nitrogen. Most trees do not suffer from lack of sufficient nitrogen. Although lawns respond quickly and dramatically to the application of nitrogen, becoming green and lush, its use should be tempered, as this lush growth is also more susceptible to attack by insects and disease. Nitrogen in best applied to cool-season grasses in fall and on warm season grasses as they begin to grow in early summer. Nitrogen should be applied to container plants in a complete fertilizer, such as 20-20-20.

Phosphorus

Lack of phosphorus typically results in reduced growth and in some plants purplish foliage, especially older leaves. Although it may be observed on container grown plants most soils in Missouri contain ample phosphorus so more rarely would deficiencies be noticed in a garden situation. If you suspect your plants are showing symptoms of lack of phosphorus, have your soil tested. Then add phosphorus as required by the test results. Container grown plants require regular fertilizing with a complete fertilizer such as 20-20-20.

Potash

Again, lack of potash is rare in Missouri soils but deficiency symptoms typically result in stunted growth. Older leaves may yellow and leaf edges may roll up. If a deficiency is suspected have your soil tested and follow the recommendations provided with your soil test results. Container grown plants require regular fertilizing with a complete fertilizer such as 20-20-20.

Calcium, Magnesium and Sulfur

These three elements complete the macronutrients. They are frequently available in adequate amounts in St. Louis soils.

Micronutrients

Several micronutrients are required for good plant growth. These include: iron, manganese, copper, zinc, boron, chlorine, molybdenum, and nickel. Symptoms are almost entirely crop specific, hence, listing general symptoms of little use. Also, their identification can be difficult from symptoms alone. Some are well known and a plant disease reference of well-studied crops may show pictures of the classic symptoms of a particular nutrient deficiency on a crop. Frequently, however, short of sending leaf tissue off to a lab for analysis the gardener is left questioning whether the symptoms they are seeing are caused by a nutrient deficiency or not. If in doubt, treat the plant with a micronutrient fertilizer or a complete fertilizer containing micronutrients. Since most micronutrients are used in very small amounts the fertilizer will provide the plant what it needs if the soil is indeed lacking in a micronutrient. Follow the product’s label directions.  In the St. Louis area the most commonly encountered micronutrient problem is with iron.

Iron

Lack of iron most notably causes what is referred to as iron chlorosis or yellowing leaves where the veins remain green. New growth is most affected. Lack of iron in the soil, a high soil pH (over 7) that restricts availability of iron in the soil, and environmental conditions can all result in iron chlorosis.  For detailed information on iron chlorosis see the IPM page “Iron Chlorosis of Trees and Shrubs” herein. Potted plants showing iron chlorosis can be watered with a fertilizer containing iron or a specific iron fertilizer such as chelated iron.

Organic Strategies

Organic fertilizer and nutrient products are available for use in correcting some deficiencies. Consult the Organic Materials Review Institute (OMRI™) for appropriate products.

More images:

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Possible nutrient deficiency on sweet potato vine (Ipomoea)
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Although the damage to this redbud (Cercis canadensis) resembles nutrient deficiency, the suddeness of onset is more typical of herbicide injury.
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The chlorosis on this sweetgum leaf (Liquidambar) is typical of a nutrient deficiency (iron, manganese or zinc) but preemergent herbicides or soil compaction could also be suspects.
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The cause of the discolored leaves on this Bradford pear (Pyrus calleryana) is unknown, but it might be due to a nutrient deficiency.
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The fescue lawn (Festuca) on the left was fertilized; the fescue lawn on the right was not.
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Too much fertilizer, as on this zoysia grass, can produce a bright green lawn but it also makes the grass more susceptible to disease and insect problems.
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