Arborists Really Know Their Trees

7bd6It is no surprise that there are many different types of physicians within the medical industries. Pediatricians, surgeons, cardiologists, dermatologists, and all sorts of ‘doctors’ are all recognized for their particular medical specialty. Yet, almost all horticultural professionals are known simply as gardeners or landscapers, even though many never work directly in gardens or landscapes.

Production nurserymen grow horticultural commodities (plants). Other nurserymen maintain these commodities while they are marketed. Landscape designers develop the landscapes that many plants inhabit. Only after the involvement of various less familiar horticultural professionals, landscapers install the landscapes, and gardeners maintain them. Somehow, they get too much credit.

Arborists really deserve more credit. They are the physicians of trees, who specialize in arboriculture, which is the horticulture of trees. Much of their work is out of reach to gardeners, and is very distinct from the sort of work that gardeners should be expected to perform. Trees are the most substantial features of a landscape, so really should get the proper attention that they deserve.

The International Society of Arboriculture, or ISA, certifies professional arborists who have passed an examination of their arboricultural expertise, and continue to demonstrate proficiency with discriminating arboricultural standards. Continued involvement with ISA classes, educational seminars and workshops is required to maintain arborist certification. It demands serious dedication.

Besides assessing the health, stability and structural integrity of trees, ISA certified arborists are the most qualified to prescribe any necessary arboricultural procedures, and to direct those who perform these necessary procedures. Most local municipalities require a report from an ISA certified arborist to accompany an application for a permit to remove any protected ‘heritage’ tree.

The website of the ISA, at, Is an excellent resource for finding certified arborists, and the tree service businesses with which they are affiliated. Arborists can be found by name directly, or regionally by ZIP code or city. The website is also a great resource for information about proper arboriculture and trees, and can help those who are not arborists with selection of trees.


Horridculture – Clearance

P90102Many arborists mark certain lengths on their pole saws and pole pruners. When stood upright, these marks designate the standard heights for minimal clearance pruning. Not so many need to mark the height of minimal clearance for walkways, since they will prune away anything that is within reasonable reach with hand tools from the ground. The minimal clearance above parking spaces is not so easy to guess at, so is more likely to be marked on poles. So is the minimal clearance over roadways, where the lowest limbs must be high enough to be out of the way of campers and freight trucks.
Clearance to the sides is determined by the location of the curb, but even that might need to be modified at sharp turns, or where the roadway slopes significantly away from the center. Clearance must similarly be a bit higher over dips in a roadway, where the height of long freight trailers would be affected by the elevation of the wheels in front and back (outside of the dips). Clearance around street lighting, roofs, utilities and such is determined by the object that requires clearance, so no marks must be made on the poles for such work. (Clearance pruning of high voltage cables is only performed by those who are qualified to do so.)
Clearance pruning is serious business for arborists. They do not want their trees to hurt anyone, or to damage vehicles. Nor do they want their trees to be damaged by vehicles. Obtrusive limbs can be torn away by freight trucks. Even if not torn away, limbs that are regularly battered by freighter trucks are rather unsightly.
As someone who used to drive the delivery truck, I can tell you that clearance pruning is also important for some of us who use the roadways.
These three young Italian stone pines are healthy specimens that are probably well structured inside all of the outer foliage. It is hard to say, since I can not see inside through all the disfigured lower foliage that has been continually battered by truck traffic. They probably only need to be pruned for clearance above and away from the traffic. If pruned to establish a minimal ceiling just two feet or so above the obvious damage, and to remove all the lower growth to the side, they would be excellent street trees for many years. They will eventually need to be pruned again, as maturing branches sag from their own weight, but that is to be expected. The main trunks and bulky limbs within would probably be quite sculptural if they were to be exposed by pruning that is necessary anyway. It really would not take much.

Prune Now For Fruit Later

70726thumbModern fruit trees have been so extensively bred to produce abundant and unnaturally large fruit, that most types are unable to support the weight of the fruit that they can produce each season. Without specialized dormant (winter) pruning to limit production, the weight of excessive fruit breaks and disfigures the limbs of the trees that produce it. Fruit becomes too much of a good thing.

Pruning not only limits the weight of the fruit; but it also improves the structural integrity of the limbs that must support it, and ideally, keeps fruit more reachable. Concentrating resources produces fewer but better fruits, instead of wasting resources on excessive fruits of inferior quality. Fewer stems that grow in spring are more vigorous and resistant to disease than more stems would be.

‘Stone’ fruits (of the genus Prunus) generally get similar pruning. However, peaches and nectarines produce such heavy fruit that they get pruned more severely than apricots, plums and prunes. Cherries and almonds are so lightweight that they may not need to be pruned at all. Cherries may be pruned for height. Since almonds get shaken from their trees, height is not so important.

Stems that grew last summer should produce fruit next summer. They should therefore be pruned short enough to support the weight of the fruit that they can produce (or what stems produced in previous years). For peaches, stems may need to be pruned to only a few inches long, even if the new stems are several feet long. Upper stems that get too high can be pruned out completely.

Apples and pears benefit from the same sort of pruning, but can be cut back even more aggressively, since their new stems tend to be more productive at the base. Crowded clusters of vigorous new stems can be thinned to eliminate the largest and most dominant stems. Stunted ‘spur’ stems that do not elongate more than two inches or so each year many not need to be pruned at all.

The ‘four Ds’, which are ‘Dead, Dying, Diseased and Damaged’ stems, are the first to get pruned out, even if they happen to be in the right places. There is just too much potential for problems later. Young trees that do not need much pruning now should be pruned for structure. Dormant fruit tree pruning is so important and specialized, that it is worth studying in more thorough detail.

Six on Saturday: Deodar Cedar Migration


Deodar cedars that were featured in the gardening column about two weeks ago, , live in a small grove adjacent to a building that I work out of. They need a bit of pruning for clearance from the roof, but are otherwise rather nice and healthy specimens.

They are also prolific. Quite a herd of seedlings is developing on the ground below. None of the individual seedlings are more than just a few years old, which suggests that the area was cleared of seedlings a few years ago. The area needs to be cleared of seedlings again, before they grow big enough to become a messy thicket.

Part of another landscape in another area happened to be in need of a few deodar cedars. There were two established specimens there already. They suit the situation so well that more are desired. However, new trees are expensive, and because there is no irrigation system in that particular site, they would need to be watered very regularly by hose until they get established.

Well, you can guess what happened. We pulled up several of the seedlings that needed to be pulled up anyway, and simply plugged them into the site where more deodar cedars are desired. It was done just prior to rain, so the relocated seedlings did not even need to be soaked in. They were pruned so that they would not desiccate so readily. We planted way more than necessary because there were plenty to spare, and also because we expect that several will not survive the process. We also expect that we will likely need to cut down a few later because, although some will not survive, too many probably will. Because they are just tiny seedlings, they will get established more efficiently than canned nursery stock, and will not be so sensitive to lapses of irrigation.

Although way more than necessary were relocated, they were not even a quarter of what was available in the original herd. More than three quarters of the herd remain available to be planted elsewhere. More will likely be relocated to other parts of other landscapes before the rainy season is half way finished. A few will be canned and put into the nursery. Whatever we do to them should be done in the early part of the rainy season to take advantage of the weather while they get established. We prefer to relocate the larger seedlings first, so that those that remain will be the smaller seedlings that will take longer to get too big to move if they must wait until next year to be relocated.

This is actually old technology, and how tree seedlings were pulled and plugged to enhance the production of woodlots since ancient history. While undesirable seedlings were pulled and discarded, more desirable seedlings that happened to be crowded around the parent trees were pulled up and plugged in more uniformly over a larger area.

1. seedlings in the ground below the parent treesP81215

2. parent treesP81215+

3. bundle of seedlingsP81215++

4. unpruned seedlingP81215+++

5. same seedling prunedP81215++++

6. seedling in new locationP81215+++++

This is the link for Six on Saturday, for anyone else who would like to participate:

Horridculture – Disdain For Bloom

P81212From the same landscape that, last autumn, was so dutifully deprived of its elegantly cascading rosemary and soon to be fiery autumn color of Boston ivy, , I procured these disturbing images of what results from of a serious disdain for flowering crabapple bloom. These trees were mentioned earlier in that article, but without such images. Similar victims were discussed last spring, and about a year ago .

The landscape where these trees live was actually rather well designed, and for a few years, had been well maintained. Seriously! The flowering crabapples were likely selected because they would not get tall enough to encroach into the utility easement above. There were pruned as much as necessary to prevent them from developing into a nasty thicket like young flowering crabapples typically do, but without significantly compromising the spectacular bloom. They really were spectacular!P81212+

About six years ago, a different crew of ‘gardeners’ was hired. It was obvious when it happened because the brutality to other features of the formerly well maintained landscape was so immediate. These flowering crabapples were somehow spared, but only temporarily. They were at their prime when they displayed exemplary bloom for the last time three springs ago. As these pictures indicate, they were hacked back two springs ago, just as the fat floral buds were showing bright pink color, and were about to pop open. All the buds and blooming stems that the trees had put so much work into were cut off and taken away, just days or maybe hours before the big show. The process was repeated in the same manner just prior to bloom last year. A scarce few twigs were somehow missed, and managed to bloom with a few blossoms that developed into the few fruits that can be seen in the second picture. I can not explain why the hacking was done earlier this year. Nor can I explain why a bit more of the twiggy growth remains. Did the ‘gardeners’ leave it for a tiny bit of bloom, or were they just lazy with their mutilation. It does not matter. As long as these trees get hacked like this, they are ruined. The client pays the ‘gardeners’ to do this.

Now, these trees could only be salvaged by renovation. This would involve pollarding, which would remove the tangles of gnarled stubs, but would leave horridly stubbed limbs to start the regeneration process. The trees would be just as deprived of bloom for the first year, but would at least be able to compartmentalize (heal) the wounds on the cleanly stubbed limbs. The secondary growth would need to be very meticulously and systematically groomed and pruned for many years to replace the canopy. It is possible, but would involve more work than even a good horticulturist or arborist would want to devote to the project.P81212++


P81208KKThe tufts of small branches that so often develop where limbs were pruned from the trunks of a coast live oaks are sometimes referred to as ‘tumbleweeds’. They are about the same size as an average tumbleweed. By the time the get any larger, most of the smaller stems have subordinated and died out, leaving only a few more defined dominant stems, which will continue the process until even fewer or a single new branch dominates. Such tumbleweeds, as well as stems that originated from such growth, are weakly attached to the main trunks. They often get pruned off for the same reason that the limbs that were there before got pruned off, or because they are expected to be weakly attached. If they remain long enough, they can of course develop into new limbs.

Tufts of the same sort of growth on sycamores or other deciduous trees are known more simply as . . . ‘tufts’ I bet you didn’t see that coming. They can get much bigger than tumbleweeds before they develop much distinction between the dominant and subordinate growth. Because tuft growth is innately vigorous, the leaves are bigger and coarser. Then, when the rest of the deciduous trees that produce them defoliate in autumn, the tufts retain their green foliage until it gets ruined by frost.

This big sycamore dropped its top over summer. The tufts developed on the big trunks that became exposed to sunlight by the loss of the upper canopy above. The tree will naturally try to replace its top, but will also naturally be even more disfigured and structurally deficient than it already was. As the tufts develop into limbs, and the limbs get heavy with foliage, they will be very likely to break away and fall. As unpleasant as all that sounds, it is quite natural for such a mature sycamore who is so old that he just doesn’t care who gets offended anymore.

Arborists Are Very Specialized Horticulturists

81205thumbThe first storm of the year has a way of reminding us if our trees need attention. Whether then need to be worked on this year or not, we tend to notice how they blow in the wind, or if they are full of dead and deteriorating debris that falls into the garden or onto the roof. As deciduous trees defoliate, they are less likely to be damaged by wind, but their structural deficiencies become visible.
This is when some of us will contact arborists to inspect and perform necessary arboricultural procedures for trees that have grown to big for us to maintain. We do not want trees to be damaged by the wind. Nor do we want them dropping limbs or falling onto whatever is within their reach. Those that are biggest and most beyond our reach have the most potential to cause major damage.
Arborists are horticulturists who specialize in the horticulture of trees, which is known as arboriculture. They assess the healthy, stability and structural integrity of trees, then prescribe necessary corrective arboricultural procedures, and if necessary, prescribe the best time for such procedures. Most arborists work with a tree service that is equipped to perform the prescribed procedures.
Arborists who are certified by the International Society of Arboriculture, or ISA, have passed an examination of their arboricultural expertise, and maintain their credential by continued involvement with the educational seminars, classes and workshops of the ISA. More information about the ISA, local certified arborists and even arboriculture, can be found at the website
As mentioned earlier, arboriculture is specialized horticulture of trees. It is not something that gardeners should be expected to perform; particularly mow, blow and go gardeners who are not even proficient with simple gardening. Many arborists can concur that unqualified gardeners sometimes kill trees, and cause much of the damage to trees that arborists must later correct. Besides, arboriculture is the sort of work that can be very dangerous to those who lack training, experience or the necessary equipment.

Bad Root Pruning

P81118-Root pruning is nothing new. It is done more commonly than we think about for many aggressive perennials like lily-of-the-Nile, that like to disperse their roots into areas where we want to grow more docile annual bedding plants or vegetables. We might do it halfway, or more, around a shrubby plant during spring or summer if we plant on digging and moving it the following autumn. For most small and low profile plants, root pruning is sort of tolerable. The plants that we do it to may not like it, but it is sometimes necessary, and better than not doing so.
Trees are not like most small and low profile plants. Most are very sensitive to root pruning when mature. They are not so proficient at replacing the portions of their root systems that they are deprived of. Large roots that get severed are very susceptible to decay, which slowly migrates inward to the rest of the root system. Obviously, depriving trees of roots compromises stability to some extent. Because roots are below grade, it is impossible to know the extent of the damage caused by root pruning while it is being performed. This is a classic example.
The exposed freshly cut surface to the left in the picture above is not the stump of a small tree that was just cut down. Although it is, in this picture, a horizontally oriented cut surface of what seems to have been something that was standing vertically, it was actually cut vertically through a horizontally oriented root. Yes, that is it in the yellow oval to the right. It was cut because it was displacing the adjacent asphalt pavement, as demonstrated by the picture below. Rather that trouble us with this concern, the resident of the adjacent home cut the root of this mature photinia tree to protect his driveway from more damage.P81118+

The problem was that the major root that was severed was all that was supporting the tree. (The cut surface of the severed root is in the middle of the picture below.) The roots to the left and right of it may seem to be substantial in the picture below, but were mostly decayed stubs left from earlier root pruning. I was able to wrestle the stump out to dispose of it, without cutting more roots. The lack of other substantial roots is probably why the primary root was so big and expanding actively enough to displace the pavement.P81118++

The funny thing about all this is that I would have done the same thing. I would have determined that, although the tree would be very distressed by the loss of such a major root, it should not have been too terribly destabilized, and should have been likely to eventually recover. Even if it eventually succumbed to the distress, the loss of this mature but small tree would have been a better option relative to continued damage to the paved driveway. I certainly would not have expected it to simply fall over as it so comically did. The picture below shows what had been vertical trunks of the photinia tree that were quite horizontal after it fell over. The fractured asphalt pavement is visible at the far right edge. The top of the tree reached the center line in the adjacent roadway. I am sorry that I did not get a more amusing picture of it blocking the lane. I was in too much of a rush to clear the roadway at the time. This was something that I really was not expecting to encounter at work.P81118+++

Big Trees Are Bad Houseplants

P81111By ‘big trees’, I don’t mean the various ficus trees that can grow up to the ceiling, and be quite happy inside. I am referring to the shade trees that live out in the yard, or forest trees that live beyond that. They are outside for a reason . . . or actually, several reasons. They are too big to bring inside. They probably would not like the climate inside. No one wants to rake fallen autumn leaves inside. Well, you get the point.
Unfortunately, on rare occasion, big trees that are outside end up partly inside by falling or dropping limbs onto the homes that they provide shade for. Just like trees seem to fall onto certain types of cars more than others ( ), trees seem to fall onto certain types of homes more than others. The difference between the homes that trees seem to dislike and the cars that they seem to dislike, is that there are actually reasons why some types of architecture is more susceptible to falling limbs or trees.
First of all, just as some trees seem to avoid falling on cars, some seem to avoid falling on houses.
Coastal redwoods in landscape situations are remarkably stable. In my entire career, I have inspected only three that have fallen. One had a massive pair of trunks that split apart and fell away from each other. Although they were on the fence line between two closely set urban homes, and there was almost no place for them to fall without destroying one home or another, they did the seemingly impossible. They literally fell onto the property line. One trunk fell out into the street. The other fell back into the backyards of the homes behind. The fence was pressed into the ground. The landscapes were seriously damaged. Gutters were stripped from both adjacent homes. Otherwise, there was NO structural damage to any of the homes. I am still amazed at how minimal the damage was!
The massive coast live oak two doors down from my former home in town was just as talented. It sprawled out over its associated home and the front yards of the two adjacent homes. It was so broad that I would not have believed that it could have fallen down without destroying one of the homes. Yet, it did exactly that . . . as I watched from my dining room. During a windy storm, it fell right toward me, and landed squarely in the front yard next door. It broke a few rafters on the edges of the eaves, and tore the gutters off, but that was the worst of the damage. It somehow found the best spot to fall where it would cause the least amount of damage.
Not all homes are so fortunate.
Victorian homes though, do not seem to be targeted by trees as much as others are. Most are closer to downtown, away from tall or very broad forest trees. Many are on somewhat narrow parcels that can not accommodate disproportionately large trees like the coast live oak in the picture above. Broadly sprawling trees tend to be too low to extend their limbs over the roofs of taller two story Victorian homes. Although taller than most other types of homes, two story Victorian homes do not occupy as much area as other homes, so are not such big targets.
Low profile homes of ranch architecture, or similar types of architecture, are more likely to be damaged by falling limbs or trees. Many happen to be located in suburban or rural areas, closer to bigger and broader forest trees. Their wider parcels can accommodate larger trees. Their roofs are low enough for trees to extend limbs over. Because they tend to be on a single level, they occupy more area, so are larger targets.

Trees Hate Cars

P71028That is a myth. They do not hate all cars. They just hate particular cars.
I did an internship with arborists in the summer of 1988, and have never been able to get away from arboriculture. Even as a nurseryman, I still sometimes work for arborists, and inspect trees that they are concerned with. I have seen many of their subject trees that have fallen onto parked cars, homes and whatever trees fall onto. I have noticed particular patterns.
Trees are more careful with Buick, Oldsmobile, Pontiac, Chrysler, Volkswagen, Mercedes Benz, and Datsun or Nissan. I have seen them put considerable effort into avoiding these cars when dropping limbs or falling over. When I was in school in San Luis Obispo, I drove my neighbor’s 1969 Oldsmobile Cutlass out from under his Chinese elm that fell over it. The tree held itself up on limbs that landed on the opposite side of the driveway so that the car came out from under it completely unharmed. When I lived in town in Los Gatos, a massive coast live oak two doors down fell harmlessly into the front yard next door. The roots pulled up in front of and behind a Volkswagen GTI that was parked at the curb, and barely tossed an ounce or two of mud onto the hood. A few big olive trees did the same at a large condominium complex in San Jose during a windy storm, leaving nothing more than a bunch of leaves and olives on top of a classic Mercedes Benz sedan and an old Datsun B210. These are certainly not the only examples. This seems to be a common theme for these particular cars.
I can not say the same for Mercury, Plymouth, Jeep, Cadillac, Mazda, Toyota, Lexus, Honda, Subaru, Infinity or Volvo. I have never seen trees damage or avoid damaging them.
Damage to Ford, Dodge, Audi, Isuzu and BMW did not see to be targeted. It was the sort of random damage that one would expect from a tree innocently falling onto parked cars.
Both of the only two cars that I know of that were squashed while being driven were Lincoln Navigators. That is not a good statistic at all. One was hit by a falling Canary Island pine in Fremont. The other was clobbered by a Coast live oak in Saratoga. No one was hurt; but the cars were killed.
I have seen only one Chevrolet damaged by a tree, but it was vicious! It was one of only three coastal redwood trees in a landscape situation that I had ever seen fall, although ‘fall’ does not adequately describe what this tree did. Without enough wind to damage adjacent and notoriously structurally deficient California pepper and Chinese elm trees, this redwood seemed to jump out of the ground to land on top of an Astro Van about twenty feet away! I do not think the tree was targeting it because it was a Chevrolet. The tree obviously hated this specific Astro Van VERY much.
Acura seems to be the second most hated sort of car among trees. They are less common than Honda, but I have never seen a Honda damaged by a tree that it did not run into first. Yet, I have seen at least three Acuras destroyed by a coast live oak, a blue gum eucalyptus and a Monterey pine. That is an inordinate number!
The car that trees seem to hate most is Porsche! They are uncommon cars, and are probably less common than any other car that I have ever seen damaged or destroyed by trees. Yet, I have probably seen more of them destroyed than Acuras, including one that was attacked as blatantly as the Astro Van was attacked by the small redwood. The ONLY blue spruce that I have ever seen fall landed squarely down the middle of a new Cayenne, back when they were the first SUV that Porsche made. The densely foliated canopy enveloped the car so thoroughly that only the middle of the tailgate was visible.
It would be interesting to know if insurance companies have determined if any particular types of cars are more likely to be damaged or destroyed by trees than any other. I would think that if the trends that I have noticed are accurate, that insurance companies would be aware of them as well. I am also curious to know if other arborists have noticed similar trends.P80106