Palms are arborescent monocotyledons that do not usually branch along their stem. Consequently, pruning landscape palms is essentially the removal of inflorescences and leaves from the lower portion of the canopy or, in the case of multiple trunked species, the removal of entire stems.
Palms are pruned for several reasons. Palm owners often want to “get their money's worth” from a pruning operation, such that palms are often radically pruned to remove all or most leaves. Although severe pruning is thought to negatively impact on the palm, complete leaf removal on sabal palm (Sabal palmetto) and pygmy date palm (Phoenix roebelenii) reduced transpiration water loss before transplanting (Broschat, 1991, 1994a). Furthermore, some landscapes require that no fronds drop to the ground to minimize hazard; therefore, it is not uncommon for palms to be pruned four times within a single year in southern California. Palms may also be pruned many times per year in an effort to control growth (Robinson, 2004). For example, Broschat and Meerow (2000) assert that removal of healthy palm leaves may lead to reduction in trunk caliper at the meristem. In macronutrient-deficient trees, removal of older palm leaves increased the severity of the deficiency in the remaining leaves and thus reduced the growth of the palm overall (Broschat, 1994b).
Current recommendations include pruning only dead, badly damaged or diseased leaves (Broschat and Meerow, 2000). Although removal of diseased leaves is sometimes recommended as a way to limit the development of diamond scale (Phaeochoropsis neowashingtoneae), severity of infection of california fan palm was not reduced even when all leaves were removed (Downer and Hodel, 2007). Hodel (1999) suggests removal of only brown leaves, cut neatly and close to the trunk, to avoid affecting the normal growth and development of the palm.
Another consideration during pruning is that tools may harbor disease inoculum. Palms are susceptible to a number of diseases caused by fungi (Downer et al., 2009; Elliot et al., 2004), some of which require a wound or injury to infect [e.g., canary island date palm wilt (Fusarium oxysporum f. sp. canariensis)]. While several treatments have been recommended for sanitizing saw blades used to remove leaves from palms (Elliot, 2006), using liquids to sanitize blades has several drawbacks: soaking takes time, solutions require frequent changing to maintain efficacy, spent solutions must be disposed in a safe manner, and the solutions may corrode tools, thereby increasing costs.
Our objective was to evaluate leaf production and growth of common landscape palm species after frequent pruning treatments, ranging from the industry standard to severe leaf removal. We also propose a novel method of saw sanitation that avoids the use of caustic liquids.
Broschat, T.K. 1994a Effects of leaf removal, leaf tying, and overhead irrigation on transplanted pygmy date palms J. Arboriculture 20 210 213
Downer, A.J. & Hodel, D.R. 2007 Leaf removal from Washingtonia filifera does not prevent infection by Phaeochoropsis neowashingtoneae but does predispose palms to early death from Gliocladium vermoeseni HortScience 42 978 (Abstr.).
Elliot, M.L. 2006 Fusarium wilt of canary island date palm Univ. Florida Inst. Food Agr. Sci. Fact Sheet PP-215/PP-139 1 June 2009 <http://edis.ifas.ufl.edu/PP139>.
Elliot, M.L., Broschat, T.K., Uchida, J.Y. & Simone, G.W. 2004 Compendium of ornamental palm diseases and disorders APS Press St. Paul, MN