Relatively little is known about the culture of ornamental palms, especially as it relates to nutrition and fertilizers. Also, much of the available information about palm nutrition from traditional sources is outdated and of little use. 

Dr. Timothy K. Broschat, of the University of Florida, has recently been investigating the nutrition of ornamental palms and has come up with new and, at times, startling information that bears summarizing here. 

This information will discuss the causes, symptoms, and diagnosis and treatment of nutrient deficiencies in palms, as well as provide a nutrition guide and a fertilizer program for palms in containers and the landscape based on some of Dr. Broschat's findings.

There are several factors to consider in determining the cause of a nutritional deficiency. In most situations, elements exist in sufficient quantities in the soil for proper growth, and it is more likely that the deficiency is due to external factors such as chemical interactions, root problems, temperature, and nutrient imbalances that render the element unavailable to the plant or limit the ability or of the plant to take up the element. However, in some cases, macronutrient, especially nitrogen, potassium, and magnesium, may simply be present in insufficient quantities. 

For example, if a grower neglects to add dolomite to the potting mixture because the pH is at an acceptable level, deficiencies of magnesium will result. Nitrogen, potassium, and magnesium are readily leached from sandy soils, such as those in some areas of Southern California, and in these cases, a complete fertilizer program is necessary. 

Since most of the now out-dated fertilizer recommendations for palms emphasized the application of large amounts of nitrogen and gave little attention to potassium, palms are often found deficient in this latter element. Adherence to sound cultural practices and a complete fertilizer program are essential to avoid nutrient deficiencies and to attain optimal growth of palms. top of page

Chemical interactions affect the solubility of elements and their subsequent availability to plants. Organic soils tend to fix copper. High soil pH decreases the solubility of zinc, iron, copper, and especially manganese, tying them up and rendering them unavailable to the plant, a not uncommon occurrence in the alkaline heavy soils of some parts of California. Generally, the best solution is applications of sulfur, incorporation of organic materials, and the use of mulches. Soluble forms of phosphate fertilizers can also tie up iron, manganese, and zinc.  top of page

Root problems due to poor aeration, disease, mechanical damage, temperature extremes, and improper planting, inevitably lead to nutritional disorders since damaged or low-respiring roots are unable to take up essential elements. In fact, root damage is one of the leading causes of nutrient deficiencies in palms, especially of some micronutrient. 

In seedlings and young plants, root diseases caused by the fungi Pythium, Phytophthora, and Rhizoctonia damage root surfaces, directly leading to decreased uptake of nutrients. Also, damaged roots will not take up as much water, resulting in oxygen-poor and/or waterlogged soil that limits the ability of the roots to take up micronutrients, especially iron and manganese. Planting too deeply results in the same problems as oxygen-poor or waterlogged soils. Any time root respiration is reduced, root activity decreases, leading to decreased uptake of iron and manganese and deficiencies of these elements. 

Mechanical injury to roots caused by improper handling at potting, repotting, planting, or transplanting will also lead to nutrient deficiencies. 

Cool temperatures also limit root activities, resulting in decreased uptake of water and nutrients. Usually cold-induced deficiencies appear in the late winter or early spring as active growth resumes and root activity is low, relative to that of the foliage. The solution is to fertilize year-round and especially in the fall before growth begins to slow down.
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Sometimes too much of one nutrient in relation to another can cause problems, even though the deficient element is still present in the soil. For example, a high nitrogen, calcium, or magnesium to potassium ratio can lead to deficiency of the latter element. If potassium is provided in a soluble form but nitrogen is supplied by a controlled-release material, more potassium than nitrogen will be leached from the soil and an imbalance between the two elements will occur. The result will be potassium deficiency. 

On the other hand, high levels of potassium and calcium may induce magnesium deficiency. For example, regular applications of a potassium fertilizer, but not magnesium, may lead to a deficiency in magnesium even though the latter element may be present in the soil. The solution here is to treat for potassium and magnesium deficiencies simultaneously. top of page

Soils vary greatly and sometimes fail to supply, in sufficient quantity, all the nutrients required for the best growth of palms. Generally, soils contain most of the elements known to be essential to plants, so one only needs to add those that are deficient in the area. For example, nitrogen is naturally low in many soils in California and additional amounts of the elements are needed for optimal growth of palms.  

Also, sandy soils are usually deficient in potassium, magnesium, and manganese. While macronutrient deficiencies are often due to inadequate levels of the elements in the soil, indicated by translucent yellow flecks when the leaves are viewed from below, this is not so for micronutrients.   return to top of page