The Mexican Fan Palm (Washingtonia robusta) is often sought for its rapid growth and tropical appearance, but it is a towering giant. This species quickly reaches heights between 70 and 100 feet, making it a dramatic vertical accent in the landscape. If the palm is already planted in the ground, permanently restricting its height is biologically impossible due to the way palms grow. Managing this palm’s size requires understanding its unique biology and employing specific horticultural practices or selecting a different species altogether.
The Biological Constraint on Palm Height
The inability to prune a Mexican Fan Palm for height reduction stems from its classification as a monocot. Palms grow vertically from a single, central point, unlike typical woody trees. This specialized growth area is the terminal bud or apical meristem, located at the top of the trunk where the fronds emerge.
The entire vertical development of the palm depends on this growth point, often called the “heart of the palm.” Severing the top of the trunk or damaging the terminal bud is lethal to the plant, as it cannot regenerate a new growing tip. Once established, the palm’s eventual height is predetermined. Pruning techniques used on deciduous trees to reduce crown size will result in the death of the palm.
Stunting Growth Through Container Planting
The only practical method to significantly restrict a Mexican Fan Palm’s size is to cultivate it in a container, which artificially stunts its growth. Confining the root system limits the palm’s ability to absorb water and nutrients, curtailing its vertical development. This technique can reduce the palm’s growth rate from up to 3 feet per year to a much slower pace, keeping it manageable for years.
To begin, select a large, sturdy container, such as a half-barrel or heavy-duty planter, ensuring it has excellent drainage to prevent root rot. Palms should be planted in a well-draining soil mix, like a cactus or palm blend, and never allowed to sit in standing water. This method requires long-term maintenance, including periodic root-pruning and repotting every two to four years to refresh the soil and prevent the plant from becoming root-bound.
When maintenance is needed, bare-root the plant and trim approximately one-third of the root mass before repotting it into the same container with fresh soil. This process is labor-intensive but maintains the restricted size and promotes long-term health in the container environment. While container growing allows for a smaller palm, it does not prevent the plant from eventually reaching an unmanageable size, which may necessitate replacement.
Managing Appearance with Proper Pruning
While pruning cannot reduce the height of a Mexican Fan Palm, it is necessary to manage its health and aesthetic appearance. The correct technique involves removing only fronds that are completely dead, brown, or damaged. Green fronds actively contribute to the plant’s energy reserves through photosynthesis, so excessive removal of healthy fronds, sometimes called “lion-tailing,” weakens the palm and makes it susceptible to stress.
A good rule of thumb is to only remove fronds that hang below an imaginary horizontal line, often visualized between the 10 o’clock and 2 o’clock positions. Pruning also removes the “skirt” of dead fronds that naturally cling to the trunk. This aesthetic choice also removes fire hazards and potential nesting sites for pests. Cuts should be made cleanly near the trunk, leaving a small portion of the petiole base to protect the trunk tissue from injury and infection.
Smaller Palm Species for Confined Spaces
If a Mexican Fan Palm has not yet been planted or its size is difficult to manage, selecting a naturally smaller species is the most reliable solution. Choosing a dwarf or slow-growing palm eliminates the need for aggressive growth restriction methods in the landscape.
The Pygmy Date Palm (Phoenix roebelenii) is a popular choice that typically reaches 6 to 12 feet. Another alternative is the European Fan Palm (Chamaerops humilis), a clumping palm that rarely exceeds 15 feet in height. For a very small space, the Sago Palm (Cycas revoluta) grows only 3 to 10 feet tall, though all parts of this plant are toxic if ingested. These smaller palms provide the desired tropical feel without the height concerns of the towering Washingtonia robusta.