Fertilization regimen reduces environmental impact of landscape palms

Palms are an important part of the environment in subtropical and warm temperate climates. Palms' aesthetics and small "footprints" make them desirable in a variety of landscapes throughout the southeastern United States. Unfortunately, palms also have some of the highest nutrient requirements of any plants. Timothy Broschat, a scientist from the University of Florida's Fort Lauderdale Research and Education Center, explained that most palms in the southeastern US are grown in sandy, nutrient-poor soils. "The result is that most landscape palms in this region are deficient in one or more elements," he said. "These deficiencies are conspicuous and unsightly; they reduce canopy size and vigor, and can become fatal for palms."

Broschat published the results of a study of areca palms in the March 2015 issue of HortScience. "The experiments were designed to determine if areca palms can be grown without supplemental phosphorus (P) in sandy or calcareous landscape soils, if areca palms can grow without supplemental nitrogen (N) during the summer rainy months of June through September in southern Florida, and if a controlled-release 0N-0P-13.3K-6Mg plus micronutrients (0-0-16) fertilizer can be used to mitigate potential damage to palms caused by application of high-N fertilizers to palms or nearby turfgrass," explained Broschat. He noted that areca palms were used because they are sensitive to all of the common deficiencies associated with palms, including nitrogen.

According to the study, current maintenance fertilizer recommendations for landscape palms in Florida entail four applications per year of a controlled release 8N-0.9P-10K-4Mg plus micronutrients (8-0-12) palm fertilizer. "However, because phosphorus and nitrogen are considered pollutants of ground and inland and coastal surface waters, it is important to apply only as much of these elements as necessary for palm health," Broschat said.

The experiments showed that areca palms growing on a sandy native soil or on a calcareous fill soil grew equally well with 8-0-12 fertilizer and the traditional 8N-0.9P-10K-4Mg plus micronutrients (8-2-12) formulation. "This indicates that phosphorus could be eliminated from the fertilizer without affecting palm growth or quality," Broschat said.

Additional results showed that fertilization with high nitrogen:potassium ratio fertilizers (typically used on St. Augustinegrass) reduced palm growth and overall quality. "These negative effects could be mitigated by supplementing these products with a controlled-release palm fertilizer having an analysis of 0-0-16-6 Mg plus micronutrients," Broschat said. "Substitution with 0-0-16 for 8-0-12 for the summer rainy season application resulted in similar palm quality to that obtained when 8-0-12 or 8-2-12 was applied year-round."

Broschat said that areca palms are susceptible to the same nutrient deficiencies as other common landscape palms, so the study results should be applicable to other species growing under similar environmental conditions.