A magnesium deficiency, although never fatal to a palm plant, can cause the development of unsightly yellow bands on the fronds. Although symptomatic leaves cannot recover, a magnesium deficiency is fairly easy to correct through the application of magnesium sulfate. Magnesium sulfate is often applied in the form of Epsom salts.
Symptoms of a Magnesium Deficiency
A magnesium deficiency first appears on the oldest palm leaves. Leaves develop broad yellow bands along leaf margins while the central portion of leaves stays green. Younger leaves have progressively wider strips of green leaf tissue. Sometimes a potassium deficiency occurs simultaneously. A potassium deficiency is indicated by necrosis on the tips of the oldest leaves, while the magnesium deficiency will force symptoms on mid-canopy leaves. Leaves between the two deficiency zones will have both symptoms in different portions of the leaves.
Causes and Related Factors
A lack of available magnesium in the soil causes a magnesium deficiency in a palm. This type of deficiency is common in soils where minerals can easily leach out with regular or excessive irrigation. Leaching is most common in sandy soils and with container-grown palms. A magnesium deficiency can be induced or exacerbated by high amounts of calcium, potassium or nitrogen in the soil. Magnesium in the soil of container-grown palms can be depleted within several months following supplement application.
About Magnesium Sulfate
Magnesium sulfate is a form of supplemental magnesium recognized most commonly as Epsom salts. As recommended by the University of Florida, apply 2 to 5 lb. of magnesium sulfate under the canopy of each palm tree four to six times per year. Less-soluble forms of magnesium sulfate may prove most ideal for this type of application. Affected trees may not recover for more than two years, but do not remove affected leaves until the magnesium deficiency is corrected and a large number of unaffected new leaves are present.
You should consider several factors when applying magnesium sulfate to palms. Epsom salts or other magnesium supplements should be applied to palms in addition to a balanced fertilizer. Offset magnesium and fertilizer applications by six weeks to avoid the possibility of salt injury. Palms grown in acidic soils may benefit more from applications of magnesium oxide or dolomite, which will permit slower release of the magnesium.