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UNIVERSITY OF FLORIDA
PALM NUTRITION GUIDE
Timothy K Broschat and Alan W Meerow University of Florida IFAS
Fort Lauderdale, Research A' Education Center
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida,' John T. Woeste, dean
Palms are among the most important ornamental plants in Florida landscapes and production nurseries. Palms suffer quickly and conspicuously from improper mineral nutrition, whether due to insufficient or incorrect fertilization. They also may exhibit certain nutritional disorders in unique ways compared to other ornamental plants. Some nutritional problems in palms are difficult to diagnose accurately because symptoms of several different mineral deficiencies may overlap. In this guide, nutritional disorders common on palms in the landscape, production field, and container nursery are discussed and illustrated. Fertilization recommendations for palms in these situations are also provided.
Nutritional disorders in the landscape or production field.
Nitrogen. Nitrogen deficiency is fairly common in Florida palms, although other elements such as K, Mg and Mn are much more prevalent and serious. Symptoms of N deficiency include an overall light green color and decreased vigor of the palm (Fig. 1). It is easily corrected by applying any N fertilizer to the soil. Leaf color quickly dark-ens in response to either soil or foliar fertilization.
Potassium. Potassium deficiency is perhaps the most widespread and serious of all disorders in Florida palms. Symptoms occur first on oldest leaves and affects progressively newer leaves as the deficiency becomes more severe. Symptoms vary among palm species, but typically begin as translucent yellow or orange spots on the leaflets (Fig. 2). These may or may not be accompanied by necrotic spots. Leaflets will typically have areas of necrosis along the margins (Fig. 3). As the symptoms progress, the leaflet or entire leaves will become withered or frizzled in appearance (Fig. 4). The midrib usually remains alive on K deficient leaves, although it may be orange in color instead of green in some species, In date palms (Phoenix spp.), symptoms are slightly different in that older leaves show an orange-brown discoloration near the tip (Fig. 5). It is also the leaflet tips, rather than the margins, that become necrotic as the deficiency progresses. The color of the chlorotic region in Phoenix leaves is a dull orange or even tan (Fig. 5), in contrast to the bright yellow of Mg deficiency (see next section and Fig. 6).
Potassium is translocated from older to new leaves as required by the palm. In severe deficiencies, the canopy will be greatly reduced in size due to the removal of K from all leaves. Once all K has been removed from older leaves, the palm will go into a state of decline, with reduced trunk diameter (pencil-pointing), and the emergence of small, frizzled or chlorotic new leaves. Without prompt treatment, the palms will usually die. K deficiency affects all species of palms, but is most severe in royal, queen, coconut, areca, and spindle palms. Treatment requires soil applications of sulfur- or resin-coated potassium sulfate at rates of 3-8 lbs. per tree 4 times per year plus half as much magnesium sulfate to prevent a K-Mg imbalance (and resulting Mg deficiency), from occurring. Symptomatic leaves on K-deficient palms will never recover and must be replaced by new, healthy leaves. In severely deficient palms, this means replacing the entire canopy which may take 2 years or longer. Foliar sprays with K fertilizers are ineffective in correcting the problem since the amount of K supplied by a foliar spray is insignificant compared to the amount needed to correct. the problem.
Magnesium. Magnesium deficiency is also quite common in Florida palms, but especially in Phoenix species. As with K deficiency, symptoms occur first on the oldest leaves and progress up through the canopy. Typical symptoms are a broad light yellow band along the margin of the older leaves with the center of the leaf remaining distinctively green (Fig. 6). In severe cases, leaflet tips may become necrotic, but Mg deficiency is rarely if ever fatal to palms.
Magnesium deficiency is best treated preventatively since treatment of deficient palms takes considerable time. As with K deficiency, symptomatic leaves will never recover and must be replaced by new healthy leaves. Applications of magnesium sulfate at rates of 2-4 lbs per tree 4 limes per year plus coated potassium sulfate at the same rate should correct the problem and prevent a K-Mg imbalance from occurring.
Manganese. Manganese deficiency or "frizzletop" is a common problem in palms growing in the alkaline soils that cover much of south Florida. Symptoms occur only on new leaves which emerge chlorotic, weak, reduced in size, and with extensive necrotic streaking in the leaves (Fig. 7). As the deficiency progresses, succeeding leaves will emerge completely withered, frizzled, or scorched in appearance and greatly reduced in size (Fig. 8, 9). Later, only necrotic petiole stubs will emerge and death of the bud quickly follows.
Manganese deficiency is primarily caused by the ele-ments insolubility at high pHs. In some palms such as coconut, which are not normally affected by the problem, cold soil temperatures during the winter and spring months reduce root activity and thus the uptake of micronutrients (especially Mn). Coconut palms severely deficient in Mn during the winter and spring will usually grow out of the problem without special treatment once soil temperatures warm up in late spring. Other palms such as queen, royal, paurotis, and pygmy date palms, are highly susceptible to Mn deficiency and must be treated with soil or foliar applications of manganese sulfate or they will likely die.
Iron. Iron deficiency is relatively uncommon in landscape palms and is not usually caused by a lack of Fe in the soil, or even by high soil pH, as in many other plants. Iron . deficiency usually appears on palms growing in poorly aerated soils or those that have been planted too deeply. Waterlogged soils and (deep planting effectively suffocate the roots. Symptoms appear first on the new leaves and in most palms consists of uniformly chlorotic new leaves (Fig. 10). As the deficiency progresses, new leaves will show extensive tip necrosis and reduced leaf size. Fairly symptoms in queen palms include pea-sized green spots on otherwise yellowish new leaves (Fig. 11). Iron deficiency symptoms can sometimes be temporarily alleviated by regular foliar applications of iron sulfate or chelates, but long term correction will only occur when the poor soil aeratian or improper planting depth that caused the deficiency.. is corrected.
Diagnosis of nutrient deficiencies by visual symptoms alone can be difficult, since some of the symptoms overlap considerably in some species. For instance, Mn and late-stage K deficiencies are easily confused on queen and royal palms. Potassium and Mg deficiencies are very similar in pygmy date palms and K and Fe deficiencies can be very similar in royal palms. Correct diagnosis can only be assured if leaf nutrient analysis is performed on symptomatic palms. Nutritional disorders in container grown palms. Palms growing in containers are susceptible to the same deficiencies that landscape palms experience, but the relativc importance of the various deficiencies, as well as their causes, are different. Container media generally are morc acid and have greater nutrient holding capacities than Florida native soils. Thus leaching and insolubility of nutrients are much less of a problem. Also, container grown palms are often fertilized with more complete slow release. fertilizers or regular liquid fertilization which prevents most deficiencies from occurring.
In containers, N deficiency is the most common deficiency and is caused simply by insufficient N in the medium (Fig. 1). It is typically the most limiting element in container production, whereas K, Mg, and Mn are much more limiting in landscape situations. Potassium deficiency can occur in containers if fertilizers having low K analysis are used, and Mg deficiency will occur if insufficient or low grade dolomite are added to the medium. Amendment of container media with dolomite is absolutely essential unless other sources of Ca and Mg are used in the fertilization program.
Sulfur deficiency occasionally occurs in containers if sulfate fertilizers are not used. Symptoms are virtually identical to those of Fe deficiency and can only be correctly diagnosed by leaf nutrient analysis. Manganese deficiency is much less common in containers since the growing medium is usually acid and Mn is much more soluble at lower pHs.
Iron deficiency is quite common in container grown palms (Fig. 10). Containers generally provide poor soil aeration at the bottom of the pot where palm roots typically are concen-uated and Fe deficiency is usually the result. Planting palms more deeply than they were originally growing, will have the same effect and is a major cause of chronic Fe deficiency in container grown palms. Although foliar sprays with iron sulfate or chelates may temporarily correct the problem, permanent correction can only be achieved by replanting the palms at the correct depth and in new, well drained media, For this reason it is important to use a container medium that will not quickly break down, resulting in finer particles and reduced aeration. Our studies have shown that dibbling of slow release fertilizers (as opposed to surface application) prevents the rapid breakdown of container media and greatly reduces nutritional problems associated with poor soil aeration.
Other essential elements such as P, Ca, Cu, Zn, B, and Cl, are occasionally found to be deficient if one of these elements is omitted from the fertilizer program, but such deficiencies are generally quite rare in container production or in landscapes.
Palm fertilization programs.
Field nurseries. Little or no research exists on fertilization rates for field-grown palms and rates will vary with the soil type and size of the palms. In general, granular fertilizers are typically applied. to the soil at rates starting at 1/2 to 1 lb for small, recently planted palms to 5 lbs. or more for large royal or coconut palms spaced 8' or more apart. Fertilizers should be broadcast or banded under the canopy of the palm, but should not be placed up against the trunk where newly emerging roots may be injured. Fertilizers should be applied 4 times per year for maximum growth, but on the more fertile marl and muck soils, fewer applications may be adequate. If granular fertilizers will be used in conjunction with drip systems, the fertilizer should be banded directly below the drip emitters .
Fertility varies greatly among soil types in south Florida, but certain nutrient elements are consistently lacking in all soil types and must be applied through fertilization. These are nitrogen (N), potassium (K), magnesium (Mg), and manganese (Mn). A good balanced fertilizer for south Florida should have 10-20% N, 5% P (phosphorus), 10-20%
K (equal to % N), 1-3% Mg, and .5% of Mn and Fe (iron). It should also contain sulfur and trace amounts of zinc (Zn), copper (Cu) and boron (B). It is very important that the N, K, and preferably also Mg be present in controlled release forms such as resin- or sulfur-coated products. Water soluble N, K, and Mg sources can be used, but they must be applied much more frequently to compensate for the rapid leaching of these elements through the soil.
Foliar fertilization is a fairly common practice in palm production. It is a rather inefficient method for providing macro-nutrient elements such as N, K, and Mg, but is very useful for supplying micronu-trients such as Mn and Fe to the plants when soil conditions prevent adequate uptake of these elements by the roots. Foliar fertilization is best used as a supplement for a normal soil fertilization program, particularly for micronutrients, and can be performed in conjunction with regular fungicide applications.
Liquid fertilization programs are not the most efficient delivery system for field nurseries, especially when overhead irrigation is used. The soluble nature of liquid fertilizer results in leaching or runoff of a great deal of the nutrients before uptake by the roots. To compensate, the grower often increases either rates or frequency of application, which results in waste and the potential for ground or surface water contamination. If drip irrigation is used in the field, injection of liquid fertilizer through the system may be cost-effective, and the problems inherent in overhead delivery may be minimized. For newly planted to 1-year old fields, a constant fertilization program delivering approximately 150 ppm of both N and K (and half as much Mg), will probably be adequate. This can be incrementally increased up to 300 ppm for 3-year and older palm fields. If a constant fertiga-tion program is considered feasible and advantageous, refer to Cooperative Extension Bulletin 231, Fertigation Management for the Wholesale Container Nursery; and Circular 695, Techniques of Diluting Solution Fertilizers in Commercial Nurseries and Greenhouses for more information. It is a good idea to have your soil and irrigation water tested before formulating the nutrient analysis of your solution fertilizer.
Container nurseries. For containerized palms, a fertilizer with a N-P- K ratio of 3-1-2 is commonly used, but a 3-1-3 is preferable. An 18-6-12 or similar slow release fertilizer is often incorporated into the container medium at planting time at a rate of 7 to 10 lbs per cubic yard. As discussed previously, dib-bling of slow release fertilizers (as opposed to surface application) is recommended over surface application and even incorporation. The extra labor costs will be offset by the added longevity of the container soil and, consequently, better growth of the crop, One and a half to three pounds of a micronutrient amendment (rate depends on product), should also be incorporated per cubic yard of planting medium. Approximately 7 lbs of dolomite per cubic yard incorporated into the mix will adjust the pH of most media to 6-6.5 and provide calcium and magnesium. If constant liquid fertilization programs will be used instead, approximately 150 ppm of both N and K (and 1/3 to 1/2 as much Mg), will probably be adequate. Leaching should be performed once a month if the crop subjected to constant fertilization is not exposed to rainfall. When soil temperatures drop below 65º fertilization rates should be reduced. A monthly foliar fertilization with a soluble micronutrient spray is favored by a number of growers. Many palm species respond favorably to such a program.
Landscape. Fertilization of palms in the landscape does not differ appreciably from recommendations for palm field nurseries, though landscape maintenance budgets may not allow as frequent an application of fertilizer. Mature palms in the landscape should optimally receive a complete granular fertilizer formulated for palms ("palm special"), four times per year at a rate of 5-8 1bs each application. Dropping below a minimum of two applications, even for the most budget conscious maintenance schedules, is not recommended. On fill soils, even two applications may not be enough. For palms under eight feet tall, 2-5 lbs should be adequate. Newly planted palms can receive even less (1/2 to 2 lbs, depending on size). Special palm fertilizers contain additional Mg and a complete micronutrient amendment. N and K rates in the formulation should be equivalent, and all or at least some of both elements should be available in slow release form. Fertilizers should be broadcast or banded under the canopy of the palm, but should not be placed up against the trunk where newly emerging roots may be injured.
Timothy K Broschat, at and Alan Meerow are Professor and Assistant Professor, respectively, Environmental Horticulture Department. University of Florida, Fort Lauderdale Research And Education Center, Fort Lauderdale, Florida 33314
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