My Palm Leaves Have Brown Spots

Q. My fan palm has black spots on the fronds.  Someone said it may lack iron.  Or, is it getting too much water?

A. Without seeing what the fronds look like I will assume it is a nutrient deficiency such as iron which is a common to desert soils. Nutrient deficiencies occur for a variety of reasons, not simply because it’s missing or unavailable in the soil.

I doubt it is a leaf disease because we have such dry weather in the desert.

First on the list of reasons is, of course, the soil. There is a lot of bad soil surrounding homes. Soils supporting the growth of palms should be amended with organic materials such as compost in a 1:1 ratio at the time of planting.

Most landscapers and homeowners don't use enough compost or don’t use substitute a soil mix instead. Soil mixes are not compost. They contain mostly sand.

Compost disappears in about 3 to 4 years if the soil is covered in rock mulch and nothing is done to add more. As a result, the soil becomes compacted, drains poorly and begins suffocating the roots of plants like palms. As roots die, these nutrient problems emerge as black spots on leaves even when fertilizer is applied. Black spots appear first on older fronds. As this condition progresses, it is seen on newer fronds.

People see palms declining in health so they give it more water. More water suffocates the roots even further and more roots die. In a slow death spiral, black spots on the fronds graduate to fronds turning yellow.

Because they are weakened, palms may become susceptible to diseases like Fusarium. Because roots are dying, palms cannot pull nutrients like iron out of the soil and the plant becomes deficient.

Amending poor soils at the time of planting and covering this soil with wood chips instead of rock improves the soil and adds nutrients as it decomposes. Organics from decomposing wood chips applied as a surface mulch improves drainage, adds nutrients and helps drain water away from the roots. The soil health improves and more critters inhabiting the soil are seen including earthworms.

Adding iron fertilizers to the soil may help in the short run. The same is true of iron applied as foliar sprays to the fronds. But water and poor drainage may be at the core of the problem and can only be corrected permanently with additions of organics like compost and wood chips as a surface mulch.

Other nutrients can cause black spots on the leaves such as potassium and magnesium deficiencies. The same approach will help with these nutrients as well.

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