Basic Palm Nutrition
What's new in palm fertilization? Actually there is quite a bit of recent research that has changed the way we fertilized palms just a few short years ago. Palm fertilizers were originally adapted from formulations used in palm plantations in Jamaica and other tropical countries. These fertilizers were designed to produce the maximum yield of fruits. Appearance of the palm was secondary, and crop harvesting depleted the palm of some nutrients faster than others.
Early research in Florida by myself and others devised a 3:1:2 ration of nitrogen, phosphorus, and potassium (i.e. 15-5-10) which worked quite satisfactorily, but there still was room for improvement. During our basic fertilizer trials we noted a particular deficiency (yellow mottling of the older leaves) that turned out to be a potassium deficiency. For that reason most of the newer palm fertilizers are a 2:1:3 or a 3:1:3 ration + 1-2% magnesium and micronutrients. Some may also contain less of the middle number (phosphorus) since our prior research showed that this nutrient tied-up certain micronutrients.
Work by Dr. Timothy Broschat has shown that soluble granular fertilizers release too rapidly making them almost impractical to use for labor cost reasons. We should also restrict the use of these "cheaper" fertilizers because of nutrient contamination of our groundwater. Our basic palm fertilizer program should be based on the use of a slow release fertilizer that allows the maximum uptake of nutrients by the palm and the minimum run-off into the aquifer.
In order to meet the basic nutritional needs of palms it is best to apply a slow release palm special fertilizer 3 times a year.
Small Palms (Pygmy dates, European Fans, etc.) ½ - 2 lbs/application
Medium Palms (True Date Palms, Queen palms) 3 - 4 lbs/application
Large Palms (Royals, Reclinata hybrids, etc.) 5 - 7 lbs/application
The fertilizer should be applied to the soil surface at the interface between the root ball and existing soil in a band as illustrated below. Slow release fertilizer work best when they are in intimate contact with the surrounding soil (scratched into the surface). Apply the fertilizer in the Spring, Summer, and Fall. If, due to budgetary constraints, only two applications/year can be made, apply them Spring and Fall. If only one application/year can be made, apply it in the Fall. Since these fertilizers contain micronutrients, they can stain concrete, so be careful in their application.
If you want an environmentally friendly and "goof-proof" method of fertilization consider using fertilizer spikes. The one that I have trialed and like the best is produced by the Lutz Corporation http://www.lutzcorp.com/. The Lutz maintenance spikes are a 6-0-6 formulation with adequate amounts of Mg, Mn, Fe, Cu, and S. Don't confuse this with the fertilizer spikes you find in the home improvement stores. Lutz fertilizer spikes are formulated with a special binder that keeps them from breaking apart when they are applied. They also slowly release over a period of time. Most importantly, the micronutrient levels in the maintenance spike and in the nutritional correction spikes are at a high enough level to bring about the desired results with the palm. These palm spikes are a favorite with arborists, landscape maintenance companies, and golf course superintendents who can safely and easily tell their labor to "go out to each palm and insert the correct number of Lutz spikes on the edge of each rootball." It's pretty hard to go wrong with this delivery method. Other Lutz spikes are specifically made to treat potassium, magnesium, and manganese deficiencies.
For a "quick green-up" on palms where a soil fertilizer injector is available you might want to apply water soluble liquid fertilizers. Use a high quality water soluble fertilizer with micronutrients, such as a tropical foliage blend, and dilute to the labeled recommendations. Remember for new palms apply only 1/3 to ½ the recommended rate for the first 18 months. Also remember, this is for a quick green-up only, it is not the best method of fertilization for an extended period of time.
Potassium - Potassium (K) deficiency is perhaps the most widespread and serious of all nutritional disorders in palms in tropical and subtropical areas. 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.
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 Mexican fan, queen, date and date hybrids, areca, and spindle palms. Remember that high levels of K can induce Mg deficiencies so use a corrective fertilizer that has both elements available. The Lutz potassium spike contains high levels of both nutrients.
Magnesium: Palms are inefficient at extracting Magnesium from the soil and often require supplemental fertilization with this nutrient. This is the reason so many people use magnesium sulfate (MgSO4) or Epsom salts on their palms. The only slow release product that I am aware of to correct this is the Lutz magnesium fertilizer spike. Epsom salts is so highly soluble that it rarely lasts in the soil past the first rainstorm. Magnesium is a macronutrient (like nitrogen, phosphorus, and potassium) and is required in large amounts by palms. Magnesium deficiencies are expressed by premature yellowing of the older fronds, while the midrib and petiole will remain green. Magnesium deficiencies are common and present in many palms.
Manganese: High soluble salts in the soil or irrigation water can create unique nutritional problems. High pH, alkaline soils, high water tables, poor drainage, and excess phosphorus tie certain micronutrients, particularly manganese (Mn). A manganese deficiency causes the new leaves to be stunted and frizzled, often causing a flat topped appearance. In severe cases the stunted leaves will be blackened and looked scorched.
To correct manganese deficiencies apply manganese sulfate (Don't confuse this with magnesium sulfate), or a complete micronutrient fertilizer around the base of the palm at the labeled recommended rate. Tecmangam is one brand name of manganese sulfate; These soluble materials should be broadcast around the palm as shown in Figure 1. Manganese is a micronutrient, so always use the lowest rate. Two applications will usually correct this problem. Do not over apply manganese or you can buildup toxic levels in the soil! Also remember that foliar sprays of micronutrients can be used to correct deficiencies, but that these products often stain masonry such as sidewalks and fountains.
An easy way to treat these palms for manganese deficiency is to use Lutz manganese palm spikes which contains both Mn and elemental sulfur to acidify the surrounding soil. Follow the rate that comes with this fertilizer product.
