Vegetation Needs Clearance From Infrastructure

There is a chimney under this overgrown vine.

It may not seem like it is so now, but evergreen trees really are messier than most deciduous trees. They probably do not produce any more debris, but they drop their debris over much longer periods of time, or at various times, or simply ALL the time. Yet, at this time of year, it seems like the deciduous trees that mostly have dropped nothing or very little since last year, are making most of the mess in the garden as they defoliate for winter.

Defoliation is only beginning, and will continue for a while. Ironically, the most impressively colorful deciduous trees happen to be those that hold their foliage for a long time, making their defoliation process linger over a few months. Even the most efficiently neat trees that defoliate in a few days tend to do so during windy or rainy weather, when we are not so motivated to go out into the garden to clean up their mess.

As the rainy season begins in a few weeks or so, the gutters on the eaves should be cleaned of debris that has accumulated since last year. This can sometimes be delayed until all deciduous trees that contribute to the accumulation of debris are completely defoliated. Generally though, homes with many or big trees (or many big trees) may need their gutters cleaned more than once as they continue to collect debris through autumn and perhaps into winter.

Any debris that collects behind chimneys, in valleys (where roof slope changes direction) or anywhere else on the roof, should also be removed. Even without gutters to collect debris, flat roofs collect whatever debris that does not get blown off by wind. Only parapet roofs that are common on so many homes of Spanish architecture collect more debris, since they are sheltered from wind.

Trees and vines should never be allowed to lean onto roofs. Vines and some densely foliated trees tend to accumulate all sorts of debris that rots and then damages the roof below. Trees that touch roofing material are abrasive as they move in any breeze.

Obtrusive trees and vines are also a serious problem for chimneys. Cypress, cedar, pine and the beards (accumulations of dead foliage) of fan palms are particularly combustible. Even after they get soaked by rain, they can quickly dry if heated by the exhaust from a chimney. Maple, ash and other trees with open canopies may not be as combustible, especially while defoliated, but can get roasted by chimney exhaust, and can interfere with ventilation.

Tipu Tree

Sidewalks and curbs prefer tipu trees.

It may not get too tall, but with appropriate pruning, the tipu tree, Tipuana tipu, spreads a broad canopy high enough to be a good street tree. A mature tree is not much more than thirty feet tall and at least as broad. Roots are not too aggressive. A slight bit of mess is rarely but actually more likely to be a problem. The pale yellowish flowers that fall early in summer are followed by a few seeds. Not too long after the seeds stop falling, the deciduous foliage starts to fall. The soft green leaves are pinnately compound, with eleven to seventeen leaflets that are about an inch and a half long. Tipu tree is still uncommon, but really should be more popular than it is.

Taking It To The Streets

Tipu tree is the topic for tomorrow.

No matter how unique the individual gardens are, conforming street trees really unify a neighborhood. Streets of tract homes are typically planted with a common street tree that is complimentary to the architectural styles of the homes, and is complaisant to the difficulties of life at the curb. Neighborhoods of mixed architectural styles sometimes have difficulty finding a tree that suits every home, so often select two or more options. Older neighborhoods are not quite as selective about conforming street trees because so many various trees get mixed in over the years.

Before selecting a street tree, it is best to inquire with the particular municipality about designated street trees. Home owners associations generally install their own trees where needed, with little or no regard for the preferences of individual residents. Some urban neighborhoods (that are not home owner associations) are nearly as selective, requiring individual home owners to maintain a specific street tree or trees. Others do not require street trees, but limit selection for those who desire them. Selection is very often limited to only a single species.

There are of course many rural and unincorporated neighborhoods without limitations for street trees, and neighborhoods where limitations simply are not enforced. However, selection should still be limited to trees that are appropriate for curbside planting. Such trees should have high branch structure so that they can be pruned for clearance above the largest of trucks that can use the roadway. They should be reasonably clean, and not produce anything that could be messy on cars parked below. Roots should be complaisant with concrete curbs and sidewalks, particularly where space is limited. Foliage and bark must be resilient to harsh exposure and enhanced glare (from surrounding pavement).

London plane (sycamore) and crape myrtle trees are the two most common street trees planted by landscapers, and are the most commonly pre-designated street trees, but are actually not the best of choices. London plane is popular among landscapers because it can survive the neglect that landscapers are notorious for, but has aggressive roots that eventually damage concrete, especially since landscapers waste so much water and keep the soil saturated. Crape myrtle is remarkably colorful both in bloom and with fall color, and has remarkably complaisant roots, but does not get tall enough for adequate clearance, and often gets infested with insects that drop sticky honeydew on parked cars.

This was the topic for yesterday.

Streets Might Benefit From Shade

Proportion is important for street trees.

Shade has become less of a priority for modern urban gardens than it still is for older and more spacious suburban gardens. Significantly less sunlight reaches the ground of such confined gardens among taller and shadier homes and fences. Even where shade might be desirable, space for shade trees might be minimal. Streets are the primary exception.

Streets, and associated curbs and sidewalks, are generally the sunniest situations within modern urban neighborhoods. They collect and radiate ambient heat that warms nearby homes and gardens, even if the weather is already unpleasantly warm. Cars that park on pavement without shade are vulnerable to the most heat, which accelerates weathering.

It is an unfortunate waste. Sunshine that is useless and undesirable on streets would be useful within gardens. Although sunlight is not transferable from one situation to another, it might be partially abatable with shade. Streets are certainly no place for gardening; but the space above them may have potential to accommodate the canopies of shade trees.

Street trees are simply trees that flank streets and other roadways. Most are shady. A few are merely visually appealing. They may inhabit parkstrips, treewells or gardens that are adjacent to sidewalks. Many municipalities prescribe street trees for most of their streets. Conforming street trees are standard accessories for streets within new residential tracts.

Of course, street trees must be appropriate to their particular applications. They must get tall enough for clearance above the largest of vehicles that use the roadways below. For commercial districts, some must also stay above storefront signs. Contrarily, a few street trees must stay below aerial utilities. Street lamps, high or low, require clearance as well.

Size and form are not the only considerations. Roots of street trees must be complaisant with infrastructure. Mess should be as minimal as practical. The most complaisant street trees might stay too small to attain adequate clearance or provide much shade. The most visually appealing might be too messy. Selection of appropriate street trees necessitates significant research regarding every potential option.

Sudden Limb Failure Jeopardizes Safety

Entire trees can also fall unexpectedly.

Windy weather sometimes breaks limbs from trees, or blows entire trees over. Evergreen trees are innately more susceptible to such damage than deciduous trees are. Wind can blow more easily through deciduous trees while they are bare through winter, when most wind occurs. However, deciduous trees are now more susceptible to sudden limb failure. 

Sudden limb failure, or spontaneous limb failure, is a result of gravity rather than of wind. It is actually more likely without wind, during mild or warm weather, particularly with high humidity. It consequently has potential to be more hazardous than limbs that blow down. More people go outside among trees during mild weather, and fewer expect falling limbs. 

Sudden limb failure occurs if limbs become unable to support their own increasing foliar weight. Warmth accelerates vascular activity, which sustains foliar growth. High humidity and a lack of wind inhibit evapotranspiration (evaporation from foliage), which otherwise helps to alleviate excessive weight. Developing fruit can also cause sudden limb failure.

In the wild, willows, poplars, sycamores, and perhaps a few other riparian trees regularly and naturally exhibit partial sudden limb failure. Limbs that fracture and sag onto soil, but remain partially attached to their original tree, can generate roots and grow as new trees. Although their strategy is practical for them, it is unacceptable within refined landscapes. 

Several native and exotic trees of chaparral climate are quite susceptible to sudden limb failure within or adjacent to irrigated landscapes. Since they are not accustomed to such abundant moisture, they overindulge. Mature wild trees are more likely to exhibit sudden limb failure after an unusually rainy and warm winter, or if rain continued late into spring.

All native oaks, particularly valley oak and coast live oak, are susceptible to sudden limb failure. So are Monterey pine and Monterey cypress. Carob, sweetgum, various elm and various eucalypti are exotic species that are notorious for such behavior. Evergreens are more unpredictable, since their new growth is less obvious among their lingering foliage. 

The Stakes Could Be High

Some unfortunate trees become so reliant on staking and straps that they are never able to support their own weight.

The irony of landscaping and gardening to bring nature closer to the home is that it is so very unnatural. Plant specie are imported from all over the world, grown in synthetic environments, and then expected to perform in unfamiliar climates and soils far from home. Most plants have been bred for optimal retail appeal at the expense of their natural adaptations.

Trees grown in nurseries need to be staked tightly to develop the sort of straight trunks that branch at just the right height to be marketable. In the landscape, trees need to be staked because they have become so dependent on the stakes that they grew up with. Eventually though, trees need to learn how to carry their own weight.

When new trees get planted and staked loosely with heftier stakes that stand up to wind, old tightly bound nursery stakes should be removed since the tight binding interferes with trunk development. By the time trees gets planted, the nursery stakes are probably nearly rotten through at the ground anyway. The new heftier stakes should not hold trees tightly in place, but simply be there to keep them from getting blown over.

Straps should likewise not be tightly bound, but instead allow for a bit of motion with the breeze. Straps should cross over in a ‘figure eight’ pattern between trees and their stakes, so that trunks do not rub so abrasively against the stakes. Most trees need only two straps each, or two pairs of straps if two stakes are used, with support up high, and lower support to prevent outward bowing. If there are no branches to hold straps in place, straps must be nailed or otherwise attached to the stakes.

Some sturdy trees, like well developed redwood trees and small magnolias, may not need stakes. Palms and yucca certainly do not. However, limber trees like the various eucalyptus may need more support than just two straps. The problem is that many trees become dependent on their stakes and will not develop strong trunks if they do not need to.

It is better to prune maturing staked trees to limit weight and wind resistance (that might cause them to blow over) than to provide more support with heftier stakes. If a maturing young tree is relying on stakes and straps for support, it needs to be pruned. A young unstaked tree that begins to lean from the weight of its canopy should likewise be pruned until it regains its posture without getting staked and bound. Trees should never be tied to other trees, buildings or anything else that can be damaged by the tension.


With all the cables coming and going, this unfortunate tree does not have much room to grow without causing trouble.

Since I did not make the drive up or down the coast very often, the rare silvery-gray Bismarck palm that I could see slowly climbing into the skyline near the edge of Highway 101 through Santa Barbara seemed to be slightly taller every time I saw it. It grew slowly, but enough to notice since I only saw it less than annually. Then, when I drove by about a month ago, it was gone.

This exemplary specimen had been quite healthy and happy (even though Bismarck palms are not supposed to be happy on the coast). There was only one problem. It was under high voltage utility cables. As it grew, it got too close to the cables, so needed to be removed in order to maintain the minimal clearance required for high voltage.

Unlike other trees, palms have only single terminal buds that grow upward. They can not develop branches to grow around cables, so only die if the single bud needs to be pruned away. Complete removal is therefore the only option when palms begin to grow into high voltage cables.

Sadly, palms often get planted under utility cables. Many Mexican fan palms grow under cables because birds that eat their fruit drop the seed there. Queen palms are popularly planted around the perimeters of back yards, and along the back fence lines that are very often directly below and parallel to high voltage cables.

Trees that are not palms can get disfigured by pruning for clearance around high voltage cables, but generally survive. Trees with central leaders (single trunks) and strict form, such as spruces and redwoods, can get be so disfigured that removal may be more practical than pruning. Trees with more irregular form, like sycamores and elms, are somewhat easier to salvage. Unfortunately, crews hired to maintain clearance are unable to prioritize the health and structure of trees that get too close to high voltage cables.

Lower cables for telephone, television and house-drops (lower voltage cables that extend from utility poles to homes and other buildings) do not often justify pruning for clearance like upper high voltage cables do. However, these lower priority cables can still be damaged if too many limbs sag onto them or become abrasive as they blow in the wind. Really, it is best to avoid problems with utility cables by selecting and planting trees that are not likely to become too obtrusive. Palms, large trees and trees that are likely to be severely disfigured by pruning to maintain clearance should be kept at safe distances.

Late Pruning For Early Bloomers

Deciduous magnolias get pruned after bloom.

Winter is generally the best season for pruning. Obviously, it is when a majority of plants are dormant, and therefore most complaisant to such potentially invasive procedures. Of course, there are exceptions to this generalization. A few plants are dormant during other seasons. Some simply prefer late pruning to accommodate their bloom or fruiting cycles.

Late pruning is important for some of the same reasons that dormant or winter pruning is important. It controls growth and directs resources. Removal of superfluous or unwanted growth reallocates resources that such growth would otherwise consume, to more useful or productive growth. The primary difference is that late pruning happens after dormancy. 

Flowering cherry trees are very similar to fruiting cherry trees, but generate only copious bloom without fruit. Flowering crabapple trees likewise produce only their unique bloom, but without much fruit. Technically, both would prefer dormant pruning during winter. Yet, late pruning immediately after bloom allows them to first bloom as profusely as they can.

Fortunately, flowering but fruitless counterparts of fruitful trees require pruning that is less severe than what their fruitful relatives require. Comparably severe pruning would be too stressful for them after dormancy. However, flowering peach trees can endure harsh late pruning to stub their bloomed shoots. Stubs generate more shoots for bloom next spring.

Late pruning begins as early as spring blooming trees and shrubs finish bloom. Because of warm weather this winter, many are blooming early. Stems of some types work well as cut flowers, either while in bloom or immediately prior to bloom. Once the first few flower buds begin to show color, most buds on the same stem should continue to bloom inside.

Camellias supposedly prefer pruning during their bloom cycle, since they resume growth immediately afterwards. Because such pruning would ruin some of the bloom that is their primary asset, most camellias must tolerate late pruning after bloom. Dogwood, forsythia, redbud, and flowering quince, as well as flowering cherry and flowering crabapple, are likewise tolerant of these technically untimely techniques.

Pollarding Pruning Techniques Remain Controversial

Pollarding is pruning to the extreme.

Olive orchards formerly inhabited some of the regions that became urban in California. A few orchard trees remained within urban gardens of the homes that encroached on them. Unfortunately, for those who did not utilize the abundant olives, these trees were horridly messy. Many decades ago, pollarding eliminated the mess without eliminating the trees.

Pollarding is extreme pruning that eliminates all but the main trunk and a few main limbs. It deprives olive trees of their ability to bloom, by eliminating stems of a previous season that would otherwise bloom during the next season. Fruit can not develop without bloom. For other trees that bloom only on older stems, pollarding eliminates bothersome pollen.

Pollarding has several other practical applications. It confines trees that would otherwise get too big for their respective situations. It enhances foliar color and texture for trees that display colorful foliage through summer, such as Schwedler and Princeton Gold maples. Red twig dogwood generates more colorful twigs, and more abundantly, after pollarding.

For agricultural purposes, pollarding generates lush vegetative growth of white mulberry to sustain silkworms, or other vegetation for livestock. It similarly generates long and thin willow stems for basketry. Various eucalypti rely on pollarding to produce juvenile foliage that is colorful and healthy enough for floral design, or aromatic enough for essential oils. 

Nowadays, pollarding is unfortunately passe and even vilified. Consequently, almost no arborists learn about it. Because it is technically disfiguring and potentially unsightly, it is undesirable for many situations. Annual repetition is needed to prevent bloom or fruiting. Otherwise, restorative pruning or more extreme pollarding eventually become necessary. 

For pollarding, proper technique is imperative. Such severe pruning must happen during winter dormancy. It would it be too stressful during vascular activity. Besides, bark would be very susceptible to scald if so suddenly exposed during warmer and sunnier weather. Pruning cuts must be very neat, and back to any old pollard cuts, without stubs to inhibit healing.

Only Arborists Specialize In Trees.

Big trees need real arborists. Even the best of gardeners should not be expected to perform major specialized arboricultural techniqes.

Just as most problems in landscapes are caused by maintenance gardeners hired to maintain the landscapes, many of the problems with trees are caused by those hired to fix such problems. Arboriculture, which is the horticulture of trees, really should be performed, or at least directed, by professional arborists. It is too specialized to expect it to be done properly by those lacking education and experience.

Even the few proficient gardeners who can perform most aspects of gardening well are not likely as proficient with proper arboriculture as arborists are, not only because it is so different from other gardening, but also because of the techniques and tools involved. Gardeners compare to arborists something like those who clean windows on skyscrapers. Custodians who clean windows on the highest floors from the inside probably would not want to clean the same windows from the outside like window washers do. There are just too many differences in the two related but vastly different types of work.

Arborists who are certified by the International Society of Arboriculture, or ISA certified arborists, are the most qualified to assess the health, stability and structural integrity of trees, and to then prescribe any necessary arboricultural procedures. These arborists have passed an examination of their arboricultural expertise, and maintain their certification by continued involvement with ISA educational seminars, workshops and classes.

Arborists and the tree service businesses that they are affiliated with are easy to find at the website of the ISA at They can be found directly by name, or regionally by city or ZIP code. The website is also an excellent resource for those wanting to learn more about trees and the importance of proper arboriculture.

Trees are the most substantial features of landscapes, and are really worthy of more respect than they commonly get. Structural problems or instability can be serious problems, not only to the affected trees, but also to anything around them that might be damaged or destroyed by falling limbs or even entire trees. Proper arboriculture helps to keep trees healthy and reasonably safe for many decades or centuries.