Ornamental palm trees are traditionally used for landscaping purposes. They are characteristic of warm temperature environments but they also show wide adaptability depending on plant species. Potassium (K) deficiency is one of the most common problems, which takes long time to recover and it could result in plant death if not treated. A constant K management with split applications helps to provide enough plant nutrients to avoid nutrient deficiencies overtime.
Palm species are popular ornamental plants for landscaping due to their glamorous and exotic shapes. Palms are typical of tropical and subtropical environments, with optimum temperature for plant growth ranging between 24 to 35°C, while water requirements will vary among plant species. Typically, it would take 5 years to grow palms in nurseries before being sold to the market to serve their purpose.
During the first 2 or 3 months of emergence, palm plants use their reserves in the seed storage tissue to grow. Thus, it is desirable to start fertilizer programs after this period to ensure efficient plant use. It is suggested also to transplant them between late spring and early fall when temperatures are warm to allow proper plant establishment and reduce plant stress.
Potassium (K) deficiency is among the most common nutrient disorders. Deficiencies are more likely to be observed in soils with poor mineral K such as Oxisols, Ultisols, Aridisols, Entisols, and Spodosols. Additionally, high concentration of cations, such as Ca2+, NH4+ or Mg2+ to K+ in the soil will cause a K deficiency.
Different species of palm have difference tolerance to lack of K in the soils. In general, the most susceptible palm species are royal (Roystonea elata and R. regia), queen (Syagrus romanzoffiana), coconut (Cocos nucifera), areca (Chrysalidocarpus lutescens), and spindle (Hyophorbe verschafeltii) palms. By contrast, other species such as, Alexandra (Archontophoenix alexandrae), spiny fiber (Trithrinaxacanthocoma), maya (Gaussia maya), and thatch (Thrinax and Cocothrinax) palms are less prone to K deficiencies.
First symptoms of K deficiency begin in older leaves, and it manifests in the new leaves as the deficiency progresses. Symptoms differ depending on fan or feather species, but usually it starts as yellow and orange spots in leaflets, which will develop into necrotic spots (see figures below). As the deficiency progresses, leaflet edges and tips will become necrotic. These will result in reduced foliage in the short term. If the deficiency persists, the plant will show reduced trunk diameter and smaller and chlorotic new leaves, finally dying.
Figure 1. K deficient Dictyosperma palm (credits Broschat, 2000).
Figure 2. K deficiency in Washingtonia robusta palm (credits Broschat, 2000).
Figure 3. Pritchardia palm showing K deficiency symptoms (credits Nelson and Patnude, 2012).
Figure 4. K deficiency in Caryota palm (credits: Nelson and Patnude, 2012).
To avoid K deficiency, it is recommended to apply from 1.5 to 4 kg of K per adult plant, using potassium sulfate (SOP) with broadcast applications, four times a year. This will provide sufficient soil K to avoid deficiencies. The use of controlled release fertilizer is suggested because when using water soluble types, they will tend to leach faster through the soil profile. Additionally, because K interacts with Mg, it is recommended to apply a ratio of 3:1 (K:Mg) to avoid nutrient imbalance. The use of foliar fertilizer to treat K deficiency is ineffective with these plant species because the amount of fertilizer delivered is minimal, compared to the amount the plant needs to correct the deficiency.
Plant recovery will take between 1 or 2 years due to slow plant growth in palms. When treating the deficiency, it is important to leave older leaves as they are a source of K for the newer tissue, if symptomatic leaves are removed, it will speed up plant death. Finally, soil analysis is an important tool to identify soil low K levels. Once the deficiency symptoms appear, it has caused plant damage already. Therefore, early diagnosis is always better to minimize potential nutritional problems over time.
Broschat, T.K. 2000. Palm nutrition guide. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Available at http://tropicalvibe.com/Palm%20Nutrition%20Guide.pdf
Garofalo, J. and Fehrman, A. Potassium deficiency of palms. Cooperative Extension Service, University of Florida. Available at https://ag.purdue.edu/agry/Purdue%20Agroecology/Documents/K-deficiency-of-palms.pdf
Geisel, P. and Le Strange, M. 2003. Palms in the central valley. Issue #3: Palm tree culture. Cooperative Extension Service, University of California. Available at http://cemerced.ucanr.edu/files/40558.pdf
Nelson, S. and Patnude, E. 2012. Potassium deficiency of palms in Hawai’i. Plant Diseases. College of Tropical Agriculture and Human Resources. University of Hawai’I at Manoa. Available at http://www.ctahr.hawaii.edu/oc/freepubs/pdf/PD-89.pdf