Andy Wilson, Senior Extension Specialist, Pinellas County Extension
Plants need 16 essential nutrients to grow and remain healthy. Deficiencies of any of these can interfere with a plant’s normal appearance, growth and other characteristics. In this article we will look at 4 very common nutrient deficiencies of plants in our area, potassium, magnesium, manganese and iron deficiencies.
Potassium is used in large quantities by plants. It is important in healthy root growth, flowering, tolerance to drought and other environmental stresses. Potassium deficiency is especially common in palms.
The symptoms vary somewhat with different kinds of palms but in general, potassium deficiency causes a premature yellow to orange discoloration of the older lower fronds, with browning of the tips of the leaflets. On some kinds of palms, like the Canary Island date palm, yellowish translucent spots also appear in the older fronds.
Potassium deficiency is also very common on orchid trees on which it produces yellowing between the veins in the leaves (called interveinal chlorosis) with some browning at the edges of the leaves and often some areas of browning between the veins of the leaves also. With mangos the older leaves brown at their tips in a way that could be easily mistaken for a fertilizer burn or browning from drought injury.
Potassium deficiencies can usually be corrected with applications of complete fertilizers or by applying potassium supplements like sulfur-coated potassium sulfate. Mild to moderate potassium deficiency on palms can usually be corrected by applying an 8-2-12-4 palm fertilizer (specifically that analysis and with micronutrients that are in the sulfate form) at least 4 times per year.
Magnesium deficiency is very common on many kinds of plants grown in our area including some kinds of palms, ornamentals, citrus and vegetables. Magnesium is a component in chlorophyll, the green pigment that is found in plants. Plants deficient in magnesium usually show a premature yellowing of the older, lower leaves that begins at the edge of the leaves and works inward or with an interveinal chlorosis of the older leaves.
Magnesium deficiency is very common on Canary Island date palm. Magnesium deficiency in palms can be confused with potassium deficiency, however, in palms magnesium deficiency doesn’t cause browning of the leaflets whereas potassium deficiency does. Often both deficiencies are present.
Magnesium deficiency is also very common on poinsettias, often appearing late in the summer. As with many other plants, magnesium deficiency causes a yellowing of the older leaves, beginning at their edges and moving inward. On poinsettias, unlike palms, after the yellowing begins, the edges of the leaves begin to turn brown and roll up and die. Eventually the leaves drop from the plant and a poinsettia plant that is severely deficient in magnesium may eventually be bare of leaves along the lower parts of the stems with only a few leaves left at the stem tip.
To prevent or control magnesium deficiency, magnesium sulfate can be applied to the soil around the plants. For plant beds the amount usually recommended is about 2 cups (one pound) per 100 square feet of bed area. For palms, about 2 to 5 pounds per palm is needed per application. Magnesium sulfate can usually be purchased where fertilizers are sold. Kieserite is a slower release, longer lasting form of magnesium sulfate that is preferable where available.
A third common nutrient deficiency of plants is manganese deficiency. Although “manganese” and “magnesium” have similar spellings, deficiencies of these two nutrients produce different symptoms. Manganese deficiency produces a yellowing between the veins of the leaves and, unlike magnesium deficiency, the symptoms begin on the newer growth. Manganese deficiency is quite common in some kinds of palms, in which it is often called “frizzle top”, since the deficiency causes the new growth to be stunted and burned in appearance. Palms can eventually die if manganese deficiency in not corrected. Manganese deficiency can be corrected with soil applications of manganese sulfate, in some cases supplemented with spray applications of solutions of manganese sulfate.
A forth deficiency is iron deficiency, and like manganese deficiency produces yellowing between the veins of the newer leaves. The main difference in the appearance of these symptoms is that the green veinal areas produced by iron deficiency are relatively narrow while those produced by manganese deficiency are broader. Iron deficiency is very common on azaleas, gardenias and ixoras.
Being aware of these common nutrient deficiencies can help you to take action to correct them more quickly if they develop in your landscape.
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