Pruning Landscape Palms

Landscape palms (Arecaceae) are pruned (i.e., leaves removed) to avoid the hazard of falling fronds, to remove diseased or brown leaves, and, in some cases, to minimize growth by diminishing photosynthetic capacity. In studies at two California locations (Long Beach and Irvine), even complete leaf removal every 3 to 4 months for 18 to 21 months resulted in similar new leaf production by queen palm (Syagrus romanzoffiana) or windmill palm (Trachycarpus fortunei) compared with no pruning or "10 and 2" pruning (industry standard pruning referring to the palm canopy visually beginning at the 10 o'clock position and ending at the 2 o'clock position on a clock face). By contrast, complete leaf removal reduced the number of new leaves of california fan palm (Washingtonia filifera), young mexican fan palm [MFP (Washingtonia robusta)], and taller, more mature MFP by 30%, 23%, and 21% compared with no pruning and "10 and 2" pruning. Leaf petiole length, leaf blade length, leaf blade width, and total palm height were also reduced 19% to 43% after complete leaf pruning compared with no and "10 and 2" pruning of young and more mature MFP. Although "10 and 2" pruning did not reduce growth of any palms, pruning all but the four newest leaves reduced leaf petiole length by 21% for the taller MFP. An important consideration for palm disease control is that tools used for pruning may harbor pathogen inoculum. Flaming pruning saws with a propane torch for 10 s reduced total fungal colonies and palm pathogenic fungi recovered on a selective medium by 95%. Increasing our understanding of palm response to leaf removal and how to minimize unintended consequences of pruning, such as the spread of disease, is an important part of improving palm maintenance.