Pruning is one of the most misunderstood aspects of palm culture. Correctly pruning any plant or tree can benefit the growth and health of the plant.
Maintained correctly, palms are low maintenance trees. For some reason, people believe they can indiscriminately hack at palms, including periodic removal of most or nearly all of the fronds (leaves), several times each year, and not harm the tree.
Palms are not an exception to good pruning rules. Poor pruning techniques will harm any plant or tree, including palms. There is a misconception that the more a palm is pruned, the faster it will grow. This is not true.
Many palm specialists discourage over-pruning except when transplanting certain species. Others simply recommend avoiding pruning as much as possible. (www.broward.org.dio5200.htm)
All green fronds produce the food needed to grow properly, producing a healthy palm. The reduction of the green leaf area reduces food production and in turn, the health and growth of the palm is placed in jeopardy. The more green leaves any plant has, the more growth that will be produced.
The only true plant food is that which the plant makes. What is purchased at stores is not plant food, even if the package says “plant or palm food.” It is nutrients (fertilizer), used by the plants with water and sunlight to make plant food.
Under ideal growing conditions, it has been found that date palms (Phoenix dactylifera) may have between 120 to 180 fronds growing up to 15 feet long. Fronds are known to live from 5 to 8 years, and in some cases up to 15 years.
Many people report Washingtonia palms have an average of 30 green fronds. I have seen as many as 50 to 60 fronds on healthy young trees. A correctly pruned palm should have an oval or circular silhouette.
There are several reasons to prune palms. You can remove dead or dying fronds that might harbor insect pests, such as roaches and scorpions, as well as removing hiding places for other pests such as rats. Excessive dead fronds are also a potential fire hazard in urban areas near homes and other buildings.
Palms can be pruned for safety reasons; so that views from driveways, sidewalks and safety signs are clear. Keep in mind, though, that blocking views is most often caused by planting a palm in the wrong place.
Planting palms too close to a building can cause damage to that structure, so they sometimes will need pruning to prevent that damage. Palms don’t need to be protected from high winds by pruning. After Hurricane Andrew, the few trees left standing were palms. Most had few if any fronds left from the high winds, but they were still standing.
When palms are field-dug and transplanted bare root, half of the fronds on most species can be removed. This reduces the transpiration rate and facilitates handling and shipping by taking up less room. After planting, fronds should be untied.
The University of Florida has found that Sabal palmettos do survive transplanting better if all fronds are removed. However, this is an exception, true only for this one species.
Palms can be pruned to remove fruit and seeds. Some palms produce seeds that germinate in the landscape or fruit that makes a mess and smells bad when it drops or is a food source for pest such as rats. Most palms do not produce either fronds or fruit large enough to cause damage when falling, nor do most palms reach a height at which this will be a problem.
Minimal Pruning Recommended
There are also several reasons to keep pruning to a minimum. Removing most of the leaves (fronds) yearly or more frequently weakens the palm and slows its growth. Mature leaves provide food for new leaves, flowers, fruit, roots and 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) removal of older green leaves facilitates deficiency because it does not allow the movement of the nutrients from the old leaves to the new ones before they die. In the case of potassium this can hasten the death of the palm. Nutrient deficiencies also cause narrowing of the trunk and decline in the size of the fronds.
Palms do not store food for future needs as well as other trees. They must have as many green fronds as possible to produce a continuous supply of food to grow and stay healthy. Research has shown the need for a 2:1 ratio between new and mature leaves in palms.
Green fronds may take three to five years to mature. A large crown of leaves on a mature date palm with over 125 leaves may have taken 15 years to develop from the newest to the oldest.
Never prune for cosmetic purposes. Some people will prune Phoenix canariensis to look like a giant pineapple or will skin the trunk of Washingtonias to look like more tropical palms. Desert palms are not tropical, so it is best to accept that, and not try to change them into something they are not.
Palms leaves are designed in a cantilever effect to facilitate survival in high winds. When too many of these leaves are removed, the palm can be more easily damaged. Removal of mature fronds takes away the protection they afford from winds to immature fronds.
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.
Most palms put on about one row of new fronds each year. Never take off more than one row.
Finally, pruning green leaves from palms also adds to the waste load at landfills.
Remember, less is more when it comes to pruning palms. If the frond is yellow or brown, prune it off.
Remove loose petioles or boots by hand. If they don’t pull off leave, them on.
Remove flower and fruit stalks. The formation of fruit and seed takes strength away from the palm unnecessarily. When mature, they may provide food for pests such as rodents and birds. Palms such as Phoenix dactylifera produce infertile or fertile fruit (if there are male trees nearby) that will later drop and is messy. Pollinated fruit of palms such as Washingtonias will germinate in the landscape.
Some clumping palms may need to be thinned out or new growth pruned off if the palm is getting too big for the space in which it is growing. (http:hort.ifas.ufl.edu/woody/pruning/palms.htm)
Some palms like Phoenix canariensis have armament that can be dangerous if people come in contact with it. This should be removed when the palm is still small. In date production the green fronds are left but the armament (spins) is removed.
When pruning tall palms, use ladders, cherry pickers (hydraulic lifts), and other non- invasive climbing gear. Climbing spikes similar to those used on utility poles should never be used, as they can damage the trunk.
Always use clean pruning equipment, including saws and pruning shears. Chainsaw blades are difficult to clean and sterilize. This is why a hand saw or a reciprocating saw (Sawzall) is recommended especially for palms that might have disease.
Disease can be transmitted from one palm to another on the saw blade. They can easily be sterilized or the blades and be replaced as with the reciprocating saw. It is recommend to sterilize equipment with a 10 percent bleach solution (1 part bleach to 10 parts water) and a 10-minute soak. (See www.Junglemusic.net) Others recommend a 50/50 solution for five minutes. Cleaning equipment in this manner will help prevent the spread of diseases such as Fusarium in Phoenix canariensis.
When pruning once or twice a year, remove all dead or dying fronds. Never take off more green fronds than can be produced in a single year.
Never top a palm tree. When a palm is topped 18 to 24 inches down from the very top of the trunk where the new leaves emerge the growing point inside the trunk is removed. The palm will then die ( if it is a signal trunked palm). If it is a multi-trunked palm only that trunk will die.
Remember safety first. Palms that have not been pruned for several years have large heavy skirts of dead fronds. Pruning these can be hazardous. The arborist needs to prune from the top down.
Never climb under the dead fronds to prune. This is a sure way to be suffocated if the skirt collapses. From 2009 to 2013, twelve people were killed in this manner. If you cannot prune from a hydraulic lift or shooting a line through the live canopy and climbing above the dead skirt, leave the pruning to someone who can do it correctly and safely.
Take a class on how to prune correctly. Contact your local Extension office or ISA representative to see when a palm pruning class will be held.
You can access the University of Nevada pruning fact sheet in both English and Spanish at. These can be printed and handed out. http://www.unce.unr.edu/publications/index.asp?Topic=Horticulture&Searchby=categorysearch&Searchtext=HO
ML Robinson is a horticulture specialist with the University of Nevada Cooperative Extension in Las Vegas. He will be speaking on pruning palms at Desert Green XVIII in Henderson, NV on November 6-7. Visit www.desert-green.org for more information.