This is a tree that takes some time to impress. Bloom is uninteresting. Foliage is no more distinctive than that of coast live oak. Instead, the most spectacular characteristic of cork oak, Quercus suber, is the boldly striated and uniquely spongy texture of its mature bark. Such bark takes a few years to develop, but gets so thick that it seems significantly older.
As its name implies, cork oak had historically been the exclusive source of bark for corks and cork products. As modern and more practical materials diminished demand for such bark, cork oak became more popular as an evergreen shade tree. It is quite happy within the arid chaparral climates of California. In fact, it behaves much like native oak species.
Mature cork oak trees generally stay less than forty feet tall, even if their trunks are wider than three feet with their unusually thick bark. Without excessive irrigation, their roots are notably complaisant. Low branches are more visibly sculptural than high branches. With pruning for adequate clearance though, trees with high branches are striking street trees. Foliar and floral debris is quite messy during spring bloom.
The parents of this unintentional hybrid are supposedly American sycamore and Oriental sycamore. No one really knows. London plane, Platanus X acerifolia, appeared within a private collection in London at the middle of the Seventeenth Century. It became popular there two centuries later, through the Victorian Era, because of its resilience to pollution.
Mature London plane trees might be taller than a hundred feet. Few here are old enough to be much taller than sixty feet though. Regardless, defoliation of such grand deciduous trees might be overwhelming through autumn. Foliar tomentum (fuzz) can be surprisingly irritating while raking too much foliage. Autumn color is unimpressively brownish yellow. The specific epithet ‘acerifolia’ translates to ‘maple foliage’, because the foliage resembles that of Norway maple.
London plane remains among the most common of street trees. It really is commendably adaptable to inhospitable urban situations. However, it is not perfect. Its roots eventually displace pavement. The foliar canopies can eventually grow disproportionately broad for compact urban parkstrips. For some people, the foliar tomentum can be a major allergen.
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.
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.
Parkstrips, those narrow spaces between curbs and sidewalks, are among the most awkward spaces in the garden. In urban areas with significant traffic, they are commonly paved over. Some neighborhoods, especially downtown neighborhoods, do not have parkstrips at all. Suburban neighborhoods though, often have wider parkstrips.
The difficulty with parkstrips is that there is so much happening around them. Cars get parked on one side. Pedestrians pass by on the other side. Driveways need to be kept clear at each end. Water meters and perhaps other subterranean utilities must be accessible.
Street trees are common features in parkstrips. They should have complaisant roots that will be less likely to displace the surrounding pavement and curbs, and high branch structure for adequate clearance above truck traffic on the roadways below. Ideally, street trees should conform with the neighborhood, and are often quite uniform. Selection of street trees should be a community effort where practical.
All other plants that go into parkstrips should be adaptable to confinement within the limited space available. They should not extend over curbs or sidewalks where they can scratch parking cars or be obtrusive to pedestrians. Parkstrip landscapes must also stay low enough so that they do not obstruct the view from cars backing out of driveways.
Because people regularly walk past or through parkstrips, thorny plants like cacti and roses should be kept back from the edges, or preferable not put into parkstrips at all. Large agaves and yuccas (with rigid leaves) are simply too big and dangerous for narrow parkstrips.
Contrary to the trend of planting vegetables in weird places, parkstrips are not good places for them either. The main problem is what dogs like to do in parkstrips. The second problem is that the good produce that might be out reach of dogs is within reach of everyone else walking or driving by. Reflected glare from all the surrounding pavement is a problem for plants that do not like harsh exposure.
Really, there are far more limitations on parkstrip landscaping than there are options. Turf grasses or tough ground cover that tolerates traffic, like trailing gazania, may seem to be a mundane, but they are practical. At least ground cover can be punctuated with clumping perennials like African iris, lily-of-the-Nile or blanket flower.
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.
Only two or perhaps three of these six pictures were taken in Watts. Furthermore, those towers in the backgrounds of pictures #3 and #4, although only a few blocks west of the Watts Towers, and supporting massive volumes of wattage, are merely electricity pylons. It is unimportant. Actually, these five images and one video are assembled together here only so that I need not discard them unused. Brent will not stop sending them. Now that these are the last for the moment, I can post more interesting or at least relevant images next week. I must share pictures of the esperanza and poinciana seed getting sown. Also, we moved a Mediterranean fan palm.
1. Brent can not stop taking selfies. Carly Simon sang about this sort of behavior in 1972; ‘You’re so vain.’ Here, he wants to be seen in a hard hat like my arborist colleagues wear.
2. Old sycamores that Brent saved from certain doom are a much more important topic. Developers who want them out of their way said that the bare deciduous trees had died.
3. Tristania laurina is an exemplary small street tree for many of the narrow streets that Brent installs street trees on. This matured crop are exemplary #5 (5 gallon) specimens.
4. Minor lower growth that got pruned away promoted caliper growth. Those are not the Watts Towers, although they are only a few blocks to the west, and support many watts.
5. Brent wants to show off a new publication that features his home garden, or his work, or some such nonsense. I did not write the particular article, so it must not be very good.
6. Brent’s home garden is SO crowded with SO much vegetation and other ‘stuff’. What a mess! It could be a hazardous situation during an earthquake. This one was very minor.
Those who crave fall color in mild climates should appreciate Chinese pistache, Pistacia chinensis. It is happy to provide fiery yellow, orange and red color in response to a slight chill. Actually, it retains its colorful foliage later into the season with mild chill than it does with frosty weather. Rain eventually dislodges all of its deciduous foliage through winter.
Because it is so resilient to harsh situations, Chinese pistache is popular as a street tree. Pruning is necessary to establish adequate clearance of broad limbs over roadways and sidewalks. Since roots can be shallow with regular watering, root barriers should protect nearby pavement. However, established trees do not need regular watering, if any at all.
Old Chinese pistache trees, as well as those that grow wild from seed, are either male or female. Female trees produce tiny but annoyingly abundant fruit. Modern cultivars are all male, and therefore fruitless. They may get more than forty feet tall, with broad canopies. The pinnately compound leaves are just about eight inches long.
Brent, my colleague down south, plants street trees. He has been doing so for decades. Some of the older trees are quite mature now. Brent telephones me to tell me whenever the first trees on opposite sides of a street meet in the middle. It is like a graduation for that particular colony of trees. The various species mature at different rates, so they ‘meet’ over their particular street on their own distinct schedule. Brent watches them all, and attends all of their ‘graduations’. Anyway, that is what the first picture reminded me of.
1. Redwoods meeting friends over a road is not uncommon here. For compact street trees that got planted at the same time on opposite sides of an urban street, it is an indication of maturity.
2. Shasta daisies are not exactly friends. They are just two of many separate flowers on the same mature plant. They are composite flowers, so each one contains many tiny but distinct flowers.
3. Lily of the Nile, while piled with many friends, waiting to get groomed and moved to another garden, looks like Sigmund the Sea Monster should stay away from the Pacific Coast Highway.
4. Deodar cedar seedlings that grew where they could not live in an industrial yard were relocated to be with friends in a landscape a few years ago. Some, although not all, are now doing well.
5. Beau, the 1967 C10, has a friend also, named Bo, and he is a 1967 C20. Beau helped me bring so much of my old plant material from the Santa Clara Valley. Bo does not get around so much.
6. Rhody is man’s best friend. Like all of his colleagues, he is very committed to his career, which is, of course, his commitment to his colleagues. In this picture, he happily awaits their arrival.
This is the link for Six on Saturday, for anyone else who would like to participate:
It is neither a fern nor a pine. Fern pine, Podocarpus gracilior, can be a tree taller than fifty feet, and half as broad, but is often a shorn shrub or hedge that can be kept less than eight feet tall. Stems are limber enough while young to be espaliered. The finely textured evergreen foliage is somewhat yellowish out in full sun, and darker green in partial shade. Individual leaves are as long as two and a half inches, and less than a quarter inch wide, and hang almost like fat pine needles. Some but not all mature trees can drop a bit of messy fruit with hard pits that are a bit larger than those of cherries. Bark gets distinctively blotched as it ages. The deep roots can be remarkably complaisant with concrete. Outer growth can get damaged by the harshest frosts every few winters or so, or roasted by hot dry heat every few summers.