Under ideal growing conditions, a young Mexican fan palm (Washingtonia robusta) can grow 6 feet a year, reaching heights of 100 feet or more. As its fronds die once a year, they cling to the young tree, although they usually drop from the canopy of a mature tree. As the dying leaves collapse against the trunk, they create a shaggy skirt of dead, dry yellow or brown leaves. Removing them can a major maintenance chore.
Mexican fan palm trunks are thick at the bottom, becoming 10 to 12 inches wide farther up. The orange stems, edged with sawtooth spines, grow clusters of about 30 fronds roughly 4 feet wide and 5 feet long. The canopies of these leaves spread 10 to 15 feet wide. Dying leaves clinging to bottom of the mature canopies can create a refuge for rats and vermin plus a fire hazard if they're struck by lightning. Many people consider the thatch a part of the character of a Mexican fan palm, while others remove them. To do that, allow the base of the dead leaves to dry completely, then prune them with a linoleum knife or another type of sharp knife. If you want to prune leaves from a tall, mature tree, you may have to hire a professional with a cherry picker. Removing the leaves create scars on the gray trunk.
Climate and Soil
Mexican fan palms grow in U.S. Department of Agriculture plant hardiness zones 9 through 11. Although they like well-drained, moderately rich soil, Mexican fan palms can survive in sand and poor soils. You can grow a young plant in a container to give your deck or patio a tropical look, but do not plant one in a small yard. Mexican fan palms need large, open areas. The Mexican fan is considered invasive in some areas. Do not plant it if you live where it is a problem.
Water and Fertilizer
Water Mexican fan palms deeply at least once a month. They will tolerate both salt and drought. Although the fertilizer needs of Mexican fan palms will vary with the soil, a general maintenance recommendation is to apply 1 1/2 pounds of 8-1-10-4 palm tree fertilizer for every 100 square feet of area every three months. An 8-1-10-4 fertilizer contains the ratio, by weight, of 8 parts nitrogen, 1 part phosphorus, 10 parts potassium and 4 parts magnesium.
Diseases and Pests
Gandoderma butt rot, a soilborne fungus for which there is no known cure, spreads upward from the soil until it destroys 80 to 90 percent of the bottom 3 to 5 feet of the trunk, causing leaves to drop and the tree to eventually die. Similarly, there is no known treatment for Thielaviopsis trunk rot, which can cause the canopy to fall off the tree without warning. You can avoid the disease refraining from pulling off lower leaves before they are ready to drop and not wounding the tree with climbing spikes or bad pruning techniques. There is no chemical cure for Fusariam wilt, a fungal disease spread by the wind and by infected pruning tools. Fusarium wilt kills the leaves and eventually the entire tree. Before and after use, and between trees, wipe pruning tools with a cloth soaked in rubbing alcohol to prevent spreading diseases. Although Mexican fan palm doesn't generally have problems with pests, avoid buying plants with visible exit holes from borers.