Magnesium deficiency is never fatal and is primarily a cosmetic problem in landscape palms. Classic symptoms are marginal chlorosis on the oldest leaves which progress upward to younger foliage.
Magnesium deficiency in Palm Trees is distinguished by a typically broad lemon-yellow band along the margin of older leaves with a green center and a distinct boundary between the yellow and green portions. If leaflet tips are also necrotic (brown dead tissue), this indicates the presence of potassium deficiency on the same leaves. As with potassium deficiency, leaves with a magnesium deficiency will not recover, and must be replaced by new healthy foliage.
Prevention and Treatment of Magnesium Deficiency
Coated or uncoated “prilled” (pelletized) kieserite can be applied to prevent or correct magnesium deficiency, but may be difficult to find. Epsom salts (magnesium sulfate) is very water soluble, and tends to leach from sandy soils very quickly. However, the use of 2 to 4 pounds of magnesium sulfate per tree along with controlled-release potassium four times per year should prevent further symptoms from occurring. If the soil pH is low, adjust using dolomitic limestone based on soil test results. Avoid the use of magnesium oxide as a treatment if the soil has a neutral or alkaline pH, as it is quite insoluble in soils with a high pH.