Institute of Food and Agricultural Sciences
Hendry County Horticulture News
Pick Palms for a Tropical Look
Palms are among the most popular and important ornamental plants in Florida landscapes. Nearly every Florida home boasts one or more of these appealing trees. Palms are prized for their unique form and the interesting texture and shapes of their leaves. The beauty, versatility, and variety of palms merit them a valued place among landscape plants in tropical and subtropical regions. The sight of an attractive palm presents a tropical look to the landscape that no other planting material can provide. Many palms are ideally suited to local conditions. There are literally dozens of different species of palms to choose from in planning a landscape for the home. Because of their relative ease of culture and minimal pest and disease problems, palms should be prominently used in the landscape. Palm trees, both exotic and native, are characteristic of the popular image of a Florida landscape scene.
In many areas of Florida the soil in which palms are grown is deficient in one or more essential nutrients. Palm trees suffer quickly and conspicuously from improper nutrition, whether due to incorrect or inadequate fertilization. Very few palms are planted are planted in native soil. In many instances, developers have removed the top soil or have had to raise the elevation of the building site with fill soil. In general, this fill is essentially inorganic sand that provides little nutrition to the plants growing in it. Often there is the additional problem of the soil being too alkaline. This often occurs where soils or the fill is derived from parent material high in limestone, such as the shell and/or coral rock which underlies much of the area. Alkaline soils "tie up" many of the essential nutrients making them unavailable to the plant. If alkaline soils are a problem, application of sulfur, incorporation of organic material into the planting area and heavy applications of mulch around the plant can be useful in lowering the pH.
Various environmental factors can influence fertilizer availability. In sandy soil, excessive rainfall or irrigation can leach fertilizer minerals from the soil and cause deficiency. Excess water resulting in flooded, waterlogged soils may damage roots so that the tree cannot properly absorb required nutrients. Low temperatures affect the uptake of nutrients by the roots. Cold induced deficiencies occur in the early spring when growth resumes while soils remain cool.
Palms generally display nutrient deficiencies in the newest leaves being formed or in the older leaves. Observation of the palm's appearance is important in diagnosing the nutrient deficiency affecting the tree. Nitrogen (N) deficiency is often observed in Florida palms, however deficiency of other elements such as such as potassium (K), magnesium (Mg), and manganese (Mn) is much more serious and wide spread. Symptoms of nitrogen deficiency include an overall light green color and decreased vigor. Nitrogen deficiency is easily corrected by adding any nitrogen fertilizer to the soil. Leaf color will quickly improve in response to either soil or foliar fertilization.
Potassium deficiency is one of the most prevalent and serious disorders in palms. Symptoms are first observed on the oldest leaves and progressively affects newer leaves as the deficiency becomes more severe. Symptoms typically begin as translucent yellow or orange spots on the leaflets. These spots may or may not have necrotic centers. The margins of the leaflets will also display necrotic edges in some instances. As the symptoms progress, leaflets or entire leaves will become withered or frizzled in appearance. In date palms, the symptoms appear as an orange brown discoloration of leaf tips. The leaflet tips rather than the margins will become necrotic. In severe cases, the tree will go into a state of decline with reduced trunk diameter and small, frizzled, chlorotic new growth. If not treated promptly, such trees will usually die. Treatment of potassium deficiency involves the application of 3 - 8 pounds potassium sulfate per tree plus half this amount of magnesium sulfate four times per year. Leaves affected by potassium deficiency will never recover and must be replaced by new healthy leaves which may take two years or longer.
Magnesium deficiency is widely encountered in palms but is rarely ever fatal. As with potassium, symptoms first become apparent on older leaves and progress upward through the canopy. Typical symptoms are a broad yellow band along the margins of older leaves with the centers of the leaves remaining green. Applications of 2 - 4 pounds of magnesium sulfate (Epsom salts) plus the same amount of potassium sulfate should correct the problem. The balance of potassium and magnesium is important in palms. Excessive amounts of one may result in the deficiency of the other. For this reason, potassium and magnesium should always be applied together.
Manganese deficiency is a common problem especially in alkaline soils. Symptoms occur on new leaves which emerge chlorotic, weak, and stunted with extensive necrotic streaking. As the deficiency progresses symptoms worsen followed by death of the growing point. Queen palms are especially susceptible to manganese deficiency. Trees may be treated with soil or foliar applications of manganese sulfate.
Since palms may take several years to recover
from nutrient deficiencies, prevention is key in preventing nutrient deficiencies.
In the past fertilizer recommendations for palms was the application
of "palm special"- a complete fertilizer specially formulated
for palms four times per year applied at the rate of 1 - 2 pounds for young
trees to 5 - 8 pounds for mature trees. The fertilizer should
be uniformly broadcast under the canopy of the palm. New research
indicates that frequent light applications of 1-2 pounds of "palm special"
once a month will give better results. On highly alkaline soils,
complete soil replacement in a broad area around and below the tree plus
generous additions of organic matter to the planting hole is recommended.
Good luck and good gardening.
Gene McAvoy is the horticulture agent with the Hendry County Extension Service. Direct your horticulture questions to PO Box 68, LaBelle, FL 33975, e-mail - firstname.lastname@example.org or phone 863-674-4092 or 863-983-1598. You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle. Office hours are from 8:00 - 5:00.
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