“Cedar” is a common name of a few species of a few genera that are not actually cedars. Western red cedar is an arborvitae. Eastern red cedar is a juniper. Deodar cedar, Cedrus deodara, happens to be one of only three real cedars. Atlas cedar and cedar of Lebanon are the other two. Cultivars of Atlas cedar are uncommon. Cedar of Lebanon is very rare.
Although too big for compact gardens, deodar cedar is one of the more popular conifers. It performs splendidly within local climates and soils, as if it is right at home. Mature trees can survive without irrigation. Roots are generally complaisant, and disperse too deeply to displace pavement. However, deodar cedar can grow fifty feet tall and thirty feet wide.
Deodar cedar mostly develop casually conical form. Some develop multiple trunks or big limbs that eventually curve upward like trunks. Otherwise, limbs tend to droop somewhat at their tips. Glaucous grayish needle leaves are about an inch or two long. Most occur in terminal clusters of short spur stems. Some develop singly on elongated vigorous stems. Foliar debris has an herbicidal effect on the ground below.
Pavement necessitates trees with complaisant roots.
Trees of substantial size are not as popular as they had been among old home gardens. Modern landscapes of bigger homes on smaller parcels can not accommodate as many. Clearance from various infrastructure is now more of a concern than shade. Within many modern urban gardens, most available space is in front. Such is the realm of street trees.
This is not because of a lack of obstacles, such as infrastructure that requires clearance. It is more because such obstacles are closer to the ground with more open space above. Many street trees must actually be more adaptable to certain constraints than other trees. Selection of such trees, if allowable by their municipalities, necessitates diligent scrutiny.
Street trees are, most simply, trees between curbs and sidewalks. Some inhabit medians while others are adjacent to curbside sidewalks. Many municipalities prescribe particular trees for particular situations. Anyone who is uncertain of such limitations should inquire. Many municipalities permit property owners to install any trees they prefer, or none at all.
For those who can select street trees, such trees must be appropriate to their application. They must grow high enough to not obstruct sidewalks or roadways. Both sidewalks and roadways require minimal clearances. So do street signs, streetlamps and traffic signals. However, street trees should not grow too large for the confined spaces that they inhabit.
This includes their roots. Aggressive roots of willows, poplars and sweetgum are likely to displace pavement. Oaks, although too big for confined situations, are more docile. Their roots are less likely to displace adjacent infrastructures. Crape myrtle has become overly common because it is too small to cause damage. It does not make much shade, though.
Crape myrtle might also get rather messy, which is another consideration for street trees. It drops flowers during summer, and can get infested with scale, which exude honeydew. Magnolias drop flowers that can be a slipping hazard. Whether deciduous or evergreen, street trees should be reasonably tidy. Over roads, they should not need much attention.
Bark was actually not Rhody’s suggestion. It was simply a convenient theme while it was difficult for me to get out to take other pictures. These are six trees that I worked around yesterday. I could recycle this theme for native species.
1. Sequoia sempervirens, coastal redwood is the Official State Tree of California, and the tallest tree species in the World. Although native, this particular specimen was grown in a nursery, and is the cultivar ‘Soquel’. It was installed into its landscape likely after 1989.
2. Metasequoia glyptostroboides, dawn redwood is the only of three species of redwood that is not native to California. It is also the only deciduous redwood. Sequoia gigantea, giant redwood, is also represented by a young tree, but I did not get a picture of its bark.
3. Prunus serrulata, flowering cherry seems to be the cultivar ‘Kwanzan’. Perhaps shade from surrounding redwoods, birches, sweetgums and dogwoods interfere with its bloom profusion. Individual flowers are a bit smaller than they should be for typical ‘Kwanzan’.
4. Betula pendula, European white birch has distinctly white bark, but also exhibits dark brown or black furrowed bark at the bases of large trunks. I tried to take pictures of both for contrast, but the white bark seemed too gray. I could have gotten both in one picture.
5. Liquidambar styraciflua, sweetgum bark goes through different phases as it matures. Young twigs initially exhibit smooth bark. Then, their smooth bark develops corky wings that grow as the stems grow. Somehow, mature bark shows no evidence of former wings.
6. Cornus florida, flowering dogwood is supposedly easy to identify by its ruff bark. I do not get it, though. Of these Six, only flowering cherry has more finely textured bark. This particular tree does not bloom so well, but produces spectacular foliar color for autumn.
Like the many different kinds of physicians who work in a hospital, there are many different kinds of horticultural professionals who specialize in particular disciplines. Although too commonly considered to be ‘landscapers’, and even though many do not work directly with landscapes, there are nurserymen, gardeners, landscape architects, horticulturists and arborists, to name a few.
Arborists specialize in the horticulture of trees. Only a few decades ago, arborists were known as tree surgeons, since they perform surgery on trees. Of all the horticultural physicians that attend to concerns in the landscape, arborists and their associated technicians are the most qualified to properly maintain trees.
Expecting a gardener to maintain large mature trees is like expecting a pediatrician to perform major surgery. Even the most proficient and educated gardeners are too specialized with maintaining other plant material in the garden to also be specialized with arboriculture, or the horticulture of trees.
Arborists who are certified by the International Society of Arboriculture, or ISA, have successfully passed and examination of their arboricultural aptitude. Certification must be maintained by attendance to educational seminars, workshops and other relevant events approved by the ISA.
The website of the International Society of Arboriculture, or ISA, at www.isaarbor.com, is the best resource for finding certified arborists and the tree service establishments that they are affiliated with. Arborists can be found within particular regions by city or ZIP code, or identified directly by name or certification number.
The ‘Public Outreach’ category at the ISA website features links to www.TreesAreGood.org, and ‘Why hire an arborist?’, as well as a few other links for consumers. After all, the website exists not only for professionals, but also to help consumers find professionals and to make responsible decisions about their trees, from the time they get planted, throughout their lifetime, and until they get old and eventually need to be removed.
The www.TreesAreGood.org link has all sorts of information about trees and their maintenance. There are many and various articles about the benefits of trees, the value of trees, tree selection, planting new trees, proper pruning techniques, insects and diseases, tree hazards, why topping hurts trees, and even an article about palms. Incidentally, the Fun Facts link mentions that the tallest tree is the coastal redwood, the biggest tree is the giant redwood, and oldest tree is the bristlecone pine, all of which are native to California.
Trees are of course the most substantial components of a landscape. Some will be around for years. Some will be around for more than a century!
Not many arborists or horticulturists are fond of the unremarkable but very popular London plane tree, Platanus X acerifolia. It soon gets too large for many of the tight situations it gets planted in, more than thirty feet broad and more than forty feet tall. Although it is among the most common of street trees, it can produce aggressive buttressed roots that displace sidewalks and curbs. Fuzz (tomentum) from the leaves is irritating to the skin or if inhaled.
Older trees that were planted prior to the development of disease resistant varieties are very susceptible to anthracnose and mildew, and are likely to infect other susceptible plants. Infected trees often get their foliage late in spring (after earlier new foliage shrivels and falls), or defoliate by late summer. Otherwise, the slightly raspy eight inch wide leaves seem sickly as they turn grungy yellowish brown in autumn.
Landscapers use London plane trees too commonly merely because they are so reliable. They tolerate most soils, smog, severe exposure (such as reflected glare from pavement) and a bit too much watering. Modern varieties are not quite as susceptible to disease. ‘Yarwood’ has large rounded leaves that are resistant to mildew. ‘Bloodgood’ is less susceptible to anthracnose. ‘Columbia’ is less susceptible to both diseases.
Large limbs and trunks with mottled gray and tan bark are rather sculptural while bare through winter. London plane happens to be conducive to annual pollarding, which makes the limbs even more sculpturally gnarly, and produces more vigorous growth with larger leaves that are less susceptible to disease.
Trees are the most significant components of the landscapes that they inhabit. They get larger than all other plants, and live for decades or centuries. Because inappropriate trees have such potential to cause such serious problems, and can be so difficult and expensive to remove, it is important to select trees that are appropriate to each particular application.
Size and form of trees when they mature are important considerations. Crape myrtles are small to midsized trees that fit nicely into tight spots, but are too dinky to be good street trees. London plane trees are more proportionate as street trees, but eventually displace sidewalks and curbs with their aggressive buttressed roots. Chinese elms can be good street trees, but need to be pruned regularly to maintain clearance. Red maples are a better choice because they get large enough without getting too big, have complaisant roots, and are easily pruned for adequate clearance.
Other features in the area can limit tree selection. Poplars and willows have aggressive roots that invade septic systems or old unsealed iron or terra cotta sewer pipes. Queen palms eventually reach utility cables, but can not be pruned to go around them. Any good shade tree can provide too much shade over solar panels. Partial shade from large trees or structures is a problem for most other trees, but is actually preferred by a few ‘understory’ trees like vine maples, Japanese maples and dogwoods.
Trees that are expected to provide shade through summer should probably be deciduous, like red oaks or silk trees, to allow warming sunlight through during winter, particularly close to the home. However, trees that should obscure unwanted views should be evergreen, like Southern magnolias or arborvitaes.
Some trees that need more attention than others are only appropriate where they will get the attention they need. Mexican fan palms are easy to care for while young, but eventually grow out of reach and need to be groomed by professional arborists. Of course, every tree is limited to particular climates. Various ficus trees that are common in nurseries in San Diego will not survive even a mild frost, which is why they are not available in San Jose.
Actually, this does not even qualify as pollarding. It looks as if this tree, which was one of a few similarly damaged Acacia melanoxylon, black acacia trees, was in the process of being removed when the crew who was removing it left for the day. It would not have been so bad if they had returned to remove it and the others completely. They did not. This was the finished product. It and the others were almost twenty feet tall in this condition. They were about twice as tall prior. This sort of hack job is what gives pollarding a very bad reputation. It also demonstrates why proper pollarding should not be so vilified that arborists do not learn how to do it. Very obviously, this is not proper. Because they could not be salvaged, all of these trees were cut down a few days after I got this picture.
Pollarding can be done for a variety of reasons, and has been done for centuries in various cultures. It is still respected technique in many or most cultures. It stimulates vigorous growth that can be fodder for some types of livestock, including silkworms who consume the vigorous foliage of pollarded white mulberry trees. It can prevent some trees from producing troublesome pollen or fruit, such as old orchard olive trees that were retained as homes and their respective gardens were constructed around them. It can enhance autumn foliar color for some types of deciduous trees, such as the old Schwedler maples that were formerly common as street trees in San Jose. It stimulates growth of vigorous cane stems that are useful for basketry, fences, trellises or kindling. Locally though, it is considered to be as egregious as the technique pictured above, which is why no one here learns about it.
Grecian bay is, as its name suggests, endemic to Greece and the Mediterranean region. California bay, Umbellularia californica, is native to California and southwestern Oregon. The two are very different. Although California bay can be useful for culinary application, it is twice as pungent. For replacing Grecian bay in recipes, half as much should suffice.
California bay also grows much larger and more irregularly than Grecian bay. With good sun exposure, it grows more than forty feet tall. Where it competes for sunlight in forests, it can grow a hundred feet tall. Domestic trees typically develop on single vertical trunks. Wild trees might develop several leaning trunks. Foliar canopies are densely evergreen.
California bay is uncommon within urban home gardens because it is so big and messy. It is more likely to inhabit rural gardens either by self sowing or by being there first. Some old trees that grew from stumps of older trees can develop basal decay. Stumps might be difficult to kill. Foliar and floral detritus inhibits smaller vegetation and seed germination. Some abhor the foliar aroma.
Horticulture is as diversified as horticultural professionals. Nurserymen grow horticultural commodities. Landscape designers plan installation of the commodities into landscapes. Landscapers construct the landscapes. Gardeners maintain them afterward. Florists use floral commodities. Arborists specialize in arboriculture, which is the horticulture of trees.
Arboriculture is necessary because trees are so substantial. Although most arborists can work with smaller trees, larger trees are their priority. Other horticultural professionals are neither qualified nor able to work with such trees. Similarly, arborists are too specialized to engage with landscape design or floristry. Arboriculture is truly an intensive discipline.
Many garden enthusiasts maintain their own trees while such trees are somewhat small. Some trees, such as dwarf citrus and Japanese maples, stay small. However, most trees eventually grow beyond reach from the ground. Even within gardens that lack gardeners, arborists might become necessary. This is certainly not something to be negligent about.
When pansies get tired in spring, gardeners can replace them with petunias for summer. Trees are completely different. They are the most substantial and persistent vegetation in their respective landscapes. Some can survive for a few centuries. The consequences of their neglect can be disastrous. Arboriculture is crucial to the safety of their environment.
The importance of arboriculture typically becomes more apparent during wintry weather. Rain destabilizes roots. Wind weakens the integrity of limbs and trunks. Generally, trees become messier and more hazardous than at other times of year. However, arboriculture is a concern throughout the year. Spontaneous limb failure is more likely during summer.
Besides, several procedures for certain trees are more appropriate during other seasons. Furthermore, mitigation of potential problems is easier before they become emergencies. Information about arboriculture is available from the International Society of Arboriculture or ISA. Their website, which also provides a list of certified arborists, is at isa-arbor.com.
Tony Tomeo 