How To Take Care Of A Mexican Fan Palm

If your yard is large enough to accommodate the fast-growing Mexican fan palm, then it is large indeed because this palm typically reaches 70 to 100 feet tall. Native to Mexico, as its name suggests, the Mexican fan palm (‌Washingtonia robusta‌, USDA zones 9 to 11) is a warmth-loving palm that is cold hardy only to about 20°F.

While these palms are relatively easy to care for, they must be protected when the temperature might dip below their hardiness range, and they also are susceptible to potassium deficiency.

Mexican fan palm trees are popular street and landscape trees with striking fan-shaped leaves that grow 4 to 6 feet long and 3 to 5 feet wide. Widely planted in California and Florida, these tall palms require full sun and well-draining soil.

They produce long, pendulum-shaped inflorescences in the spring, which become tiny black fruits of no interest to people but attractive to birds. The dead leaves droop against the trunk to create a sort of hula skirt below the canopy, which can create a fire hazard.

Find a nice sunny spot where your palm can soar to the sky and its dead, drooping fronds won't hover over structures. Plant the palm in well-draining soil in spring or summer, when the palm is likely to produce the most roots.

Water the young palm deeply immediately after planting and ensure even moisture for about six months after planting. Avoid saturating the soil, however, as these palms can develop root rot if they sit in water.

Fertilizing and Irrigation

While your palm may thrive without fertilizer, a regular application of a balanced fertilizer formulated for palms is helpful to support its fast growth rate, such as a product with an NPK ratio of 12-4-12. Palm-formulated fertilizers usually include supplemental magnesium, since palms tend to have magnesium deficiencies.

The palm's native habitats usually have deep subsurface water, so if your climate is arid, Mexican palms may need supplemental irrigation. They are mostly drought tolerant once established.

Pruning Mexican Fan Palms

When pruning palms, it's all about the dead fronds. Prune these off to avoid creating a fire hazard. After the tree reaches about 30 feet, it will become "self-cleaning," meaning it will begin to drop these dead leaves on its own—and just in time!—because who wants to teeter on an 80-foot ladder with a pruning saw?

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Unfortunately, Mexican palms are susceptible to nutrient deficiencies and several diseases.

‌Potassium Deficiency

Potassium deficiency is pretty much a given with fan palms. If you notice the tips of the leaves turning brown, watch out; the entire leaf may then turn brown, die and fall off. The trunk may also begin to taper toward the top.

To address a potassium deficiency, apply a slow-release fertilizer of the formulation 8-2-12-4 Mg or 8-0-12-4 Mg, where the first three numbers equate to nitrogen, phosphorus and potassium, while the fourth number is magnesium (Mg). If there has been extensive damage, it may take up to three years for a full canopy of green leaves to develop.

Rotting Fungal Diseases

Several fungal diseases can cause trunk or root rot, including Ganoderma butt rot, Thielaviopsis trunk rot and Phytophthora bud rot.

These can be fatal, even in mature trees, so if your palm begins to rapidly lose leaves, wilt or develop cankers (called "conks"), get the advice of a specialist. If the trunk begins to collapse, it is too late.

To help prevent these types of diseases, avoid damaging the base of the trunk with a lawnmower or other tool, and don't try to remove leaves before they drop off on their own, because these can leave wounds that will be open to disease.