Potassium (K) deficiency is a widespread problem in palms growing in sandy or calcareous soils in southeastern United States. Its symptoms are highly conspicuous, reduce palm aesthetic appeal, are difficult to correct, and can be exacerbated by nitrogen (N) fertilization. The objective of this study was to determine the optimum fertilization rates and ratio for N and K in areca palm [ Dypsis lutescens (H. Wendl.) Beentje & J. Dransf. and Mexican fan palm ( Washingtonia robusta H. Wendl.) growing in a calcareous sandy fill soil. Both species had their highest quality when fertilized with 12.2 g·m −2 N and 12.2 g·m −2 K from controlled-release (2–3 month release) sources every 3 months. Actual N and K application rates were better predictors of palm quality than N:K ratio at the highest fertilization rates that would be recommended for field nursery production. However, at lower application rates more typical of those used for landscape palm maintenance, palm quality improved as the N:K application ratio was decreased.