By Len Phillips
Arbor Age Magazine, September 2010
Palms are monocots, which means palm trees do not have continued outward growth in their trunks like a typical tree. A palm’s growth comes from the expansion of existing tissues rather than the production of new cells.
Many palms maintain a set number of live fronds. A regular turnover of foliage occurs as dying lower fronds are replaced by new ones at the bud. These dead fronds are not detrimental to the health of the tree.
If there are an excessive number of older yellow fronds, determine the cause before pruning. A nutrient problem caused by a deficiency of potassium or magnesium could worsen if the palm is pruned or fertilized with high nitrogen or the wrong type of fertilizer.
- Poor pruning techniques will harm any tree, including palms. Many palm specialists discourage over-pruning, except when transplanting certain species. Other palm specialists recommend pruning as little as possible.
- Green fronds produce the food that a palm needs to grow and remain healthy. Reduction of the green leaf area reduces food production and that, in turn, jeopardizes the health and growth of the palm. The only true palm food is that which the plant makes. Fertilizer is used by trees along with water and sunlight to make food.
- Under ideal growing conditions, date palms (Phoenix dactylifera) can have between 120 to 180 fronds, each growing up to 15 feet long. Fronds are known to live from five to eight years. This includes leaf primordia in the apex. Many experts report Fan palms (Washingtonia robusta/filifera) have an average of 30 green fronds. A correctly pruned palm should have an oval or circular silhouette.
- Palms do not need pruning or protection from high winds. Their flexible leaves and low wind resistance make them nearly storm-proof.
- "Hurricane pruning,” which occurs in many regions is a bad practice. In the desert Southwest, the practice is referred to as "rooster-tailing,” due to the plumed appearance of the remaining leaves. Rooster-tail pruning is harmful in several ways. Instead of protecting the palm from high winds, the practice actually weakens the canopy. The reason for this is that all fronds in the apex act together, with each frond layer supporting and adding strength to the one above. They all protect the bud and newly emerging spear leaf. The more leaves removed, the less strength and protection there is.
If you damage a palm’s trunk while pruning, there is a good chance the damage will not heal. Most palm species with trunks rarely branch, so extra care should be taken because if the growing part is damaged the palm's trunk is damaged.
When to prune palms
- To remove dead and dying fronds and loose petioles that are weakly attached to some palms. Palm leaves and leaf stems are heavy and can place people and property at risk should they fall from tall palms.
- To remove fronds that might harbor insect pests, such as roaches and scorpions, as well as provide hiding places for other pests such as rats.
- Removing dead and dying lower fronds improves the appearance of a palm.
- To remove potential fire hazards in urban areas near homes and other buildings.
- For safety reasons, so that signs can be seen and views from driveways and sidewalks are clear. Blocked views are most often caused by palms growing in the wrong place.
- To prevent damage to buildings and walls during high winds. Planting palms too close to a building can cause damage to the structure. Palms themselves don’t need to be protected from high winds. After Hurricane Andrew, the few trees left standing were palms. Most had few if any fronds left, but they were still standing.
- To remove spines when the palm is still small and it is near walkways or driveways. Some palms like the Canary Island date palm (Phoenix canariensis),have sharp spines that can be dangerous if people come in contact with them.
- Some clumping palms may need to be thinned out or new growth pruned off if the palms get too big for the space in which they are growing.
To remove fruit clusters, especially in public landscapes where falling fruit and flower debris can be messy and/or hazardous. Some palms generate copious amounts of seedlings near the parent. When mature, fruits may provide food for pests such as rodents and birds. The formation of fruit and seed takes strength away from the palm.
Rules for pruning
- If the frond is yellow, brown or broken, prune it off. If green fronds must be removed, prune off as few as possible. Under no circumstances should palms be severely pruned. Severe pruning is characterized by the removal of fronds between the ten-o-clock and two-o-clock positions on the palm canopy. Never take off more green fronds than can be produced in a single year.
- Remove loose petioles or boots by hand. If they don’t pull off, leave them on.
- Climbing spikes damage the trunks of palms and may spread diseases from tree to tree when not sterilized.
- Always use clean pruning equipment, including saws and pruning sheers. Chain saws are difficult to clean and sterilize, and should not be used to prune fronds from palms. Pruning saws must be immersed in a 50/50 solution of bleach and water for five minutes. Cleaning equipment in this manner will help prevent the spread of diseases such as fusarium in date palms.
- There is never any good reason to top a palm. Most palms are single-trunked, having only one growing point. Once that growing point or bud is damaged or killed, so is the entire palm. Research has shown that buds of Washingtonia and Phoenix palms are 18 to 24 inches down from the emergent point (or very top of the trunk). Some people mistakenly think that topping will shorten a palm that has grown too tall or that it will make the palm branch like a regular tree. Both cases are false.
- A trunk can be removed from clumping palms such as the Mediterranean palms (Chamaerops humilis), and the rest of the palm will live -- although they may become susceptible to ganoderma.
- When tall palms need pruning, uses ladders or aerial lifts, and non-invasive climbing gear.
Reasons to minimize pruning
- Removing most of its fronds yearly or more frequently weakens a palm and slows its growth. Mature fronds provide food for developing fronds, flowers, fruit, roots and storage reserves in the trunk.
- When green fronds are removed, the nutrients they would have produced are lost to the rest of the palm. Some nutrients move from older leaves to newer leaves as they die. With potassium and, to lesser extent, other nutrients deficiencies, removal of older green or chlorotic leaves exacerbates the deficiency. Nutrient deficiencies also cause narrowing of the trunk and decline in the size of the fronds. The palm must now obtain its potassium from younger leaves in the canopy. These previously green and healthy leaves will then become chlorotic and unsightly.
- Palms must store sufficient reserves of starch in their trunks to restore fronds in the event that a palm experiences some type of stress such as fire, frost or defoliation by storms or humans.
- Palms must have as many green fronds as possible to produce a continuous supply of food. Research has shown the need for a 2:1 ratio between juvenile and mature fronds in some palms.
- Fronds may take three to five years to mature. A large crown of leaves on a mature date palm with more than 125 fronds may have taken 15 years to develop from the most juvenile frond to the most mature frond. This includes primordial leaves in the bud that have not yet emerged.
- Never prune for cosmetic purposes. Some people will prune Canary Island date palms to look like giant pineapples, or will skin fan palms to look like more tropical palms. Desert palms are not tropical, and it is best to accept that and not try to change them into something they are not.
- Palm leaves are carried in a cantilever effect to facilitate survival in high winds. When too many fronds are removed, the palm can be more easily damaged. Immature fronds that have been robbed of the support and protection of mature fronds are more susceptible to wind damage, desiccation and structural failure.
- Research has shown that mature fronds are those found below the current year’s blooms. When pruning, leave at least two rows of mature fronds, preferably more.
- Never take off more leaves in one year than are produced during that time. Research indicates that each species of palm has a set number of live green fronds with the same number of developing fronds inside the bud area of the palm. As new fronds emerge, the oldest fronds die. The age of a mature frond will be determined by many factors, including size of the palm, species, number of fronds produced, etc. The key point is that only the palm "knows” when a frond needs to be pruned off and when it is dying.
- Severe pruning stimulates an unhealthy survival response in palms. Energy is burned to quickly produce new leaves, to replace those lost, so severely pruned trees begin depleting their reserves of energy. If this happens on an annual basis, the palm’s trunk gradually decreases in diameter and becomes weak. This weakened trunk is more likely to break or shatter in a storm.
Because palms are not as efficient as other trees at storing food for needy times, they are more dependent on their leaves to provide necessary food for growth. With relatively few leaves, removing even one green frond can significantly reduce a palm's ability to feed itself. Palm trees must have as many green fronds as possible to produce a continuous supply of food to grow, stay healthy, and build storage reserves.
Len Phillips can be reached via e-mail at firstname.lastname@example.org
Issue Date: September AA 2010, Posted On: 9/27/2010
- Personal communication with Ken Pfalzgraf
- Gilman, Edward F., "Pruning Palms,” UF/IFAS, 2007.
- Robinson, M. L., "Pruning Palm Trees,” University of Nevada Cooperative Extension, 2004.
- Begeman, John, "Be Prudent Pruning Palms,” College of Agriculture and Life Sciences, The University of Arizona, 1999.