Palm Pruning*
Brief Description of the Palm Family
All palm species are found in but one plant family, the Palmae (or Arecaceae). There are
somewhat more than 200 genera and almost 3000 known species. It should come as no surprise
that almost all species are tropical or subtropical in origin.
Palm species range in size and form from small trunkless shrubs to towering 200-foot-tall trees. Some are vines, and many have clumping or clustering trunks. Those species that produce aboveground stems may have trunks that are as thin as half an inch or as stout as 4 feet or more in diameter. Only one genus of palm has naturally branching stems, although several species will branch as a result of injury to the trunk or growing point (apical meristem). Many palms have spines, teeth, or prickles on their stems, leafstalks, and sometimes on the leaves themselves.
The leaves of palms are among the glories of the entire plant kingdom. They range from 6 inches to more than 70 feet long and are of two basic forms: palmate and pinnate. Palmate leaves are round or semicircular in outline and may or may not be deeply segmented, while pinnate leaves are linear, oblong or triangular in outline with segments arranged in the fashion of a feather and sometimes fused into an apparent undivided blade. All palm leaves have stalks, although some are short. Almost all palm species have leaves only at the end (top) of the trunk, but a few of the climbing types have their large leaves spaced at regular intervals for considerable distances along the stems.
Palm habitats include all types of environment except the very cold montane regions and the polar. The family has representatives in the mangrove coastal environment, estuaries and fresh water swamps, the oases of deserts, tropical and subtropical coastal plains and grasslands, deciduous tropical forests, rain forests (both lowland and montane and both tropical and warm temperate), and even in the drier regions of mountains; and at least one species is a true submerged aquatic. The greatest diversity of the family is attained in tropical forest regions, especially humid and moist forests where many of the smaller palm species are understory subjects, the larger species finding homes in clearings and along riverbanks. The only growth form not represented in the family is that of the true epiphyte. The natural range of the palm family is almost worldwide, as far north as southern Europe and as far south as the north island of New Zealand; and many species are represented in horticulture in even higher latitudes.
Palms are monocots and, as such, do not produce successive layers of growth in their trunks or stems. The trunks may enlarge with time, but not because new wood is being created; rather, the trunks increase their diameters with expansion of the tissues first formed. This fact has one important implication: injuries to palm trunks are permanent and are not repaired by the plants; therefore care should be taken in pruning and long range maintenance of the palm. Also, since very few trunked palms naturally branch, killing or removing the growing point means the death of that stem or trunk and, for the solitary-trunked species, death of the plant.
The roots of palms grow in a manner similar to that of the trunks; they branch but little and do not increase in size with the growth of the aboveground parts. But most importantly the roots of palms originate after the seedling stage only from the trunk itself. There is no greatly dichotomizing underground root network as there is with an oak or other dicotyledonous tree, although the root systems of large palms may range far from the trunk near the surface of the ground. The implication is that palms are mainly surface feeders and usually need regular supplies of moisture and soil nutrients. True desert palms are never found away from streams or underground sources of water.
Reasons for Pruning PalmsA palm tree is, except for some special aesthetic considerations listed below, a low maintenance landscape subject.
Aesthetic: Doubtless the most common ornamental palm planted in the U.S. is the Mexican fan palm, Washingtonia robusta. Probably the second most popular is the only other representative of the genus, the California fan palm, Washingtonia filifera. Both these species often have a very characteristic and mostly picturesque shag of dead leaves, someties called a "petticoat." These petticoats are the adherent dead leaves whose leafbases often refuse to fall from the trunk unless pulled, cut or burned off, the latter phenomenon being a common natural occurrence in their native desert and arid grassland regions. The palms seldom retain enough dead leaves in moist and humid climes to form the petticoat but, in more arid regions like southern New Mexico, southern Arizona and all of southern and coastal California, they usually do. Some palm owners love the shag, especially that of the California fan palm; other owners detest it and call it an "ugly haystack." The easiest way to remove the shag is, of course, one leaf at a time; i.e., as the individual leaves die and become pendent, they are removed. Unless the owner wants a clean and smooth look to the trunk, the petioles may be severed by nothing more sophisticated than a pair of loppers or lopping shears, which will leave the leafbases (which are usually called "boots") adherent to the trunk. For tall palms a ladder (or climbing by means of belts) is also a necessity. In humid climates these boots will fall away with time; in more arid regions they are often a permanent part of even tall trunks, only gradually falling away near the base of the trunk with maturity of the palm.
And then there is the "manicurist mentality": those who want palms like Washingtonia robusta to have clean and smooth trunks from the very bottom all the way to the leaf crown. This look is quite popular mostly in southwestern amusement parks and fantasy parks like the Las Vegas "strip." The removal of all adherent leafbases (or boots) from these palms creates an undeniably enchanting tableau because of the elegantly thin and tall trunks, but the procedure is both time consuming and labor intensive, especially for tall specimens, and W. robusta can grow (and rather quickly) to a height of 40 feet and very old palms may attain a height of 100 feet. The boot removal necessitates strength to pull the younger leafbases from the trunks, and often requires a large linoleum knife or similar instrument and, of course a ladder (or climbing gear) for the taller specimens. A chain saw is sometimes employed, but it takes not only strength and a steady hand (in order to not mar the wood of the trunk) but also usually something more substantial than a ladder, something like a cherry-picker, for the taller specimens. For shorter palms a person with strength and a steady hand may skip the lopper segment of leaf/boot removal and cut both leaves and boots in one operation with a chain saw, the caveat being the necessity to avoid cutting into the live leaves and, of course, the trunk.
The above discussion of Washingtonia palms applies equally to other popular palms in the U.S. such as the much slower growing and not nearly so massive windmill palm or chusan palm, Trachycarpus fortunei, as well as to Brahea (Erythea) palms, also known as hesper and Guadalupe palms. All these palms are relatively hardy fan palms which, in arid or semi-arid climes, are capable of amassing a shag or petticoat of dead leaves and persistent boots or leafbases and, in the case of the windmill palm, furry or hairy trunks if the shag does not remain. Grant Stephenson, plant broker and owner of Horticultural Consultants in Houston, Texas, creates a unique and beautiful finish to windmill palm trunks by first pulling the natural fibers (hairs) from the trunks and then polishing the wood with a sidewheel grinder/sander with attached fiber buffing wheel. The result is a faintly ringed but nearly smooth stem of truly elegant proportions because of the natrually quite thin trunks without their adherent mass of fibers.
Some palms are variable as to when the leafbases fall, and many others have leaves whose laminae (the main leafblades) will fall off while the boots themselves, and sometines most of the petiole, may adhere for some time. A prime example of this latter phenomenon is the palmetto of the southeastern U.S., Sabal palmetto, whose dead leafbases may adhere for most of the life of the slow growing palm, turning quite woody and usually much lighter colored than the actual "bark" of the palm, and giving a most picturesque wicker look to the trunks. The woody boots of this palm are often trimmed with a chain saw to conform one to the other in appearance and to create an even more elegant and manicured look.
Other palms retain their dead leaves and boots for much shorter periods of time than Washingtonia species; while some--especially the more tropical pinnate-leaved types with crownshafts--have leaves whose dead leafbases along with the rest of the leaf fall within a very short time after dying, leaving a naturally "clean" trunk. Popular palms in the U.S. which hold onto their dead leaves for only a short time (or for no time) and which are large landscape subjects include the following:
Just what the stems of these "clean-trunked" species looks like depends on the exact species, but almost all produce ringed trunks, some with faint and closely spaced rings (the slower growing species), others with beautiful, distantly spaced and quite prominent rings, reminiscent of large tropical bamboo culms (stems); the rings are, of course, the only remaining evidence of where the leafbases were formerly attached to the developing trunk.
Some popular palms like the Canary Island date produce immense and quite rounded canopies of long pinnate leaves. I personally consider this aspect of these palms their most desirable trait; but there are those who feel the palm looks better when only the leaves that do not fall below the horizontal plane are left on the tree. The removal of these pendent and "errant" leaves is no greater a task than the procedure of removing the "petticoats" of Washingtonia palms and, since the Canary Island date grows more slowly than either Washingtonia species, the task need not be done as often. A pair of lopping shears suffices to sever the petioles and a large linoleum knife (or a chainsaw) easily removes the leaf bases if that is desired. Most pruners leave the boots of the just-cut crop of leaves, which practice results in a picturesque, large rounded knobby cluster (usually called "the bulb" or "pineapple") of these leafbases directly beneath the leaf crown, a bulb of boots which, by the time of the next leaf pruning, will have mostly fallen away from the trunk naturally. Sometimes the caretaker will remove the bulb also, which results in an even more picturesque look, a more tropical and more airy aspect.
The larger Phoenix species, like P. canariensis and P. dactylifera (the true date or edible date), have trunks with naturally beautiful and somewhat knobby patterns of leaf scars (the visual evidence of leafbase attachment to the trunk), in a tight spiral pattern of diamond-shaped scars; but this natural look is often "enhanced" by palm enthusiasts like Grant Stephenson of Houston, Texas who uses a chainsaw to remove the protrusions (knobs) of the leaf scars, leaving a quite elegant, nearly smooth surface, but one with the beautiful diamond pattern--the procedure also results in a beautiful lighter color to the trunk of the date palms.
Some palms grown in the U.S. are clustering species which have unique aesthetic and maintenance characteristics. A prime example is Phoenix reclinata, the Senegal date palm from tropical Africa. The plants form many suckers or subsidiary trunks throughout their lives, and a single specimen may have as many as two dozen trunks. The trunks are not straight, but lean gracefully outward from their points of origin, attaining a maximum height of about 30 feet. Each beautifully ringed trunk usually carries between 20 and 30 leaves, each of which is about 15 feet long with many bright green leaflets growing at several angles from the rachis; the lower leaflets are reduced to very vicious spines 3 to 6 inches long. Few natural phenomena are as beautiful as a large "tuft" of this palm, but the clumps are made even more graceful and dramatic if a few trunks are thinned out as the mass develops so that they are of differing heights and so that the individual beauty of each trunk and the exquisitely graceful tableau of trunks and crowns can be seen and appreciated to its fullest. I have seen this palm planted as a hedge, with the many young trunks of evenly spaced plants completely obscured by a tangled mass of foliage; the visual effect is anything but attractive. If a hedge barrier is wanted using this palm, it is infinitely more aesthetically pleasing to let a few trunks of varying heights form first and then allow the many subsequent suckers to form the desired barrier at the base of the larger ones. The thinning of trunks should, of course, be done when the subsidiary stems are young and short, and the task is easily accomplished by a large pair of lopping shears to cut off the growing point--which will kill the developing trunk, allowing it to soon decay sufficiently so that it can be easily pulled apart--or to carefully cut at the base of the developing stem with a chain saw.
For most palms the rapidity with which the dead leaf parts fall from the trunks is a matter of environmental conditions, as already implied in the discussion of the two Washingtonia species. The factors which influence the fall are, of course, wind, abrasion, fire, rain and humidity (both of which precipitate the breakdown of the dead leaf), and vandalism. The latter factor is, of course, completely due to the intervention of humans. In many parts of the southwestern U.S., juvenile (and sometimes not so juvenile) miscreants are wont to create "fireworks" by setting fire to the petticoats of both Washingtonia species and, in the state of Israel, there has been a veritable rash of these occurences in the last few years.
Of course it is better to not plant any tree where it is or can become undesirable, looking crowded and cramped, or obstructing a desirable view. In practice however this situation often occurs because the person who planted the palm did not know the ultimate dimensions of the particular species or just wanted its juvenile look for a certain period of time. In many instances the desirable, ultimate and overall landscape use of the palm warrants temporary pruning of its leaves, so that, in time, it will be a positive component of the landscape. In such instances it should be remembered that, as with any other type of tree, the palm needs a certain amount of functioning leaves for proper photosynthesis and health, the amount of which varies slightly from one species to another but, in general, is sabout 50% of the total. If too many leaves are constantly removed over a given period of time, the palm’s trunk is subject to exhibiting varying trunk calipers vis-à-vis how much sugar it could produce at a given point in time; and the sight of a palm trunk with constrictions and bulges in what should be a columnar or naturally tapering stem can ruin an otherwise beautiful landscape subject.
Human Safety: The reader will probably have already surmised that the above discussion of the torching of Washingtonia "petticoats" is a prime example of a safety concern. The conflagration may be induced not by vandalism alone, but also by such incidents as the careless tossing of live cigarettes and cigars by passersby and also lightning strikes and even (in rare instances) damaged live electrical wires in a windstorm. In addition these masses of dead and dry leaves can be a habitat for all manner of vermin, including roaches, obnoxious bird species like starlings, scorpions, rats, mice and even small snakes. Grant Stephenson reports success in keeping these various animals from entering the petticoat or the leaf crowns of other palm species with a spray of ammonia and water (equal parts) on the surface of the petticoat or the leaf crown of a palm like the Canary Island date.
Few palms produce large enough leaves and/or grow tall enough for their falling leaves to be much of a danger. But some, like the coconut (Cocos nucifera) and large date palms like Phoenix canariensis, not only attain great heights but have large and heavy leaves with massive petioles and rachises. In addition the coconut produces clusters of very large and heavy fruit whose natural abscission (upon completely ripening) from their fruit stalks and consequent rapid descent can (in rare instances) be deadly. As can be imagined, removal of these leaves and fruits from tall specimens is somewhat labor intensive, especially if there are very many specimens to deal with.
A few tropical palm species have natural rings of large spines at regular intervals around their trunks (for example the macaw and grugru palms, Acrocomia spp.), rings whose removal from the purview of passing humans poses no significant problem as the spines are easily removed with shears or small branch cutters. And there is one species native to the southeastern U.S., the fan-leaved needle palm (Rhapidophyllum hystrix), whose short, clustering trunks bear fairly long and stout needle-like spines which are the metamorphosed old leafbases. This latter example is, however, seldom a safety hazard as the leaves themselves bear no spines and the leaves are carried on long petioles.
Much more common in the U.S. are those palm species whose leaves have vicious spines for a part of their length. Prime examples are all Phoenix species (date palms) whose lower (basal) leaflets are always metamorphosed into spines of varying lengths and viciousness. When young, the older, lower and more spreading leaves of these palms are often removed if they are near human pathways, and they often are.
Health of the Palm: There are only two instances in which pruning is involved in the good health of a palm: transplantation and disease cure/prevention. Leaf pruning, especially of bare-root or balled and burlapped plants, is usually a necessity when transplanting. Removing at least half the leaf crown is almost always recommended in these cases in order to reduce moisture loss through transpiration because of the inevitable root loss. Indeed, with Sabal palmetto (and all other Sabal species) the recommendation is to remove all leaves except the "spear" or newest unfurled leaf, as the roots of this palm will all die under such circumstances and the palm will have to grow an entirely new set from the trunk itself.
The prevention and cure of disease by leaf removal involves several types of fungus infestations. The two most common fungus problems are graphiola or false smut and diamond scale. The latter, in spite of the name, is not a scale insect but rather a fungus which produces scale-like lesions. The fungus problem must first be identified (which is a large subject and not in the scope of this article) and then the leaves with the worst infestations should be completely removed and burned and the proper fungicide applied. In addition there is a deadly and incurable fungus diesease (fusarium wilt) most rampant in California, that is transferred by pruning tools, as the fungus organism resides in the sap of the tree. In all cases, but especially in California, pruning tools should be sterilized between pruning one palm tree and another.
Glossary
Bipinnate (by-PIN-nait). A pinnate leaf whose primary leaflets have been replaced by
separate and smaller stalks that then bear their leaflets with or without individual
stalks.
Compound leaf. A leaf that is composed of two or more separate and differentiated leaflets.
Costapalmate (koast-a-PAHL-mait). A term used only with palmate-leaved palm species to denote the intrusion of the petiole into the blade of the leaf, thus giving the leaf a midrib or rachis to some extent, that it otherwise would not have.
Crownshaft. A term used only with pinnate-leaved palm species to denote an area just above the woody part of the trunks of certain palms; the area is more or less columnar in shape and usually smooth, and consists of the expanded and very tightly packed leaf bases of the leaves presently on the palm.
Deltoid (DEL-toid). Triangular-shaped, with the broader part near the point of attachment.
Dichotomous. Arranged in a succession of two-forked divisions.
Dicot (DY-kaht). An abbreviated form of the word "dicotyledon" or "dicotyledonous." A dicot seed produces seedlings with two seed leaves (cotyledons) as opposed to those of monocots (an abbreviated form of the word "monocotyledon"), which produce seedlings with only one seed leaf or cotyledon. Dicots have woody tissues as opposed to monocots; almost all true tree species are dicots. In addition the flowers of dicot (dicotyledonous) plants have their parts in fours or fives as opposed to those of monocots whose flower parts are in threes or multiples of three.
Epiphyte (EP-i-fyt). A plant that grows upon another plant without invading the tissues of the latter plant.
Leaflet (LEEF-let). One of the distinct divisions (blades) of a compound leaf.
Monocot (MAHN-o-kaht / MO-no-kaht). An abbreviated form of the word "monocotyledon" or "monocotyledonous." A monocot produces seedlings with only one seed leaf (cotyledon) as opposed to those of dicots (an abbreviated form of the word "dicotyledon"), which produce seedlings with two seed leaves or cotyledons. Monocots do not usually produce woody tissues as opposed to dicots and, except for palms and a few other large monocots like the dragon tree (Dracaena draco), do not result in tree forms. In addition, the flowers of monocotyledonous plants have their parts in threes or multiples of three as opposed to dicots whose flower parts are in twos, fours, fives, or multiples thereof.
Palmate (PAHL-mait). Descriptive term for the overall shape of a splayed hand or a compound or segmented leaf denoting a hand or fan-shaped placement of the leaflets or segments.
Petiole (PEET-ee-ol). The primary stalk of a simple or compound leaf.
Pinnate (PIN-nait) leaf. A compound leaf whose leaflets are arranged on opposite sides of the rachis and consist of more than three leaflets.
Rachis (RAIK-is). The primary and central stem of a compound leaf from which leaflets or subsidiary leafstalks arise; the midrib.
Robert Lee Riffle
Author of The Tropical Look: An Encyclopedia of Dramatic
Landscape Plants, available through Amazon.com (click on the
title above to order or to get more information on this book).
* This article was originally published in Arbor Age magazine, August 1998; reprinted here with permission.
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