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Chinese Elm

Chinese elm is sculptural and textural.

Dutch elm disease became a serious problem for American elms in the 1930s. However, it did not reach California until half a century or so later. Chinese elm, Ulmus parvifolia, is not very susceptible to the disease, but is a vector. In other words, it can survive infection to share it with other species of elm. Consequently, it became unavailable by the 1980s.

Some mature specimens of formerly common Chinese elm still inhabit older landscapes. Younger specimens in newer landscapes are mostly ‘Drake’ Chinese elm. They are a bit more upright, with more symmetrical form. More importantly, they are not vectors of Dutch elm disease. Other cultivars that are also resistant are rarely available at local nurseries.

Classic and formerly common Chinese elm can eventually grow more than fifty feet high. Some can grow thirty feet wide to shade an entire urban front lawn. Some cultivars might grow nearly as high, but are generally not quite as broad. Their blotchy gray and tan bark adorns curvaceous limbs. Their small deciduous leaves are not very colorful for autumn. They can be copious, messy and quite tedious to rake.

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Cork Oak

Cork oak develops sculptural trunks and branch structure with striking bark texture.

Portuguese neighborhoods in San Jose and other big cities might be identifiable by the presence of the otherwise rare cork oak, Quercus suber. After all, they are native to Portugal, as well as Spain, Sardinia, Corsica, Sicily and the coast of the Mediterranean Sea as far east as the eastern tip of Italy on the north, and the northwest corner of Libya on the south.

Like redwoods, cork oak is one of the few species of trees that survive forest fires by being less combustible. Their foliage and small twiggy stems may burn, but larger limbs and trunks are insulated by very thick cork cambium (bark). Most other trees that are adapted to burning either disperse their seeds as they burn in order to get a head start at reforestation afterward, or simply resprout from their roots.

 Ironically, this bark that is intended to help the trees survive was actually the reason why trees on the north coast of Algeria were so extensively and detrimentally harvested during French  colonialization. Corks made from the bark were needed for the wind industry in France. Fortunately, cork in Algeria is now harvested like it is in other regions, without harming the trees that produce it.

Compared to other oaks, cork oak is not too large. It can get a bit more than fifty feet tall and nearly as wide, but takes a century or more to do so. It can actually stay proportionate to urban landscapes for a very long time. Roots are mostly complaisant. The main problem with cork oak is that it drops its evergreen foliage constantly, and drops floral debris and acorns for a few months.

Gnarly trunks and limbs with spongy bark are the main appeal. The one and a half or two inch long leaves are not so interesting. They are barely convex, often with a few blunt lobes, and dull grayish green from below.

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Osier Dogwood

The soft yellow or rusty red bare stems of osier dogwood have better color where exposed to cold and sunlight.

New spring foliage will soon be obscuring the rusty red or light yellow stems of osier dogwood, Cornus sericea (or Cornus stolonifera). Because this odd dogwood is grown for these distinctively colorful stems instead of blooms, it can be pruned harshly before foliation, to promote more twiggy growth for next winter. Unpruned plants form thickets five to ten feet high and ten or more feet broad. The flowers are actually rather pathetic relative to those of other dogwoods, since they lack colorful bracts. Where exposed to frost, the opposing two or three inch long and one or two inch wide leaves can provide nice reddish autumn color.

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Even bare trees have style.

This big perennial ‘sticks of fire’ produces a thicket of bright yellowish orange stems that changes shades through the seasons.

Everyone knows that flowers provide color in the garden, particularly through spring and summer. As blooms become less abundant in autumn, fall color of deciduous plants and trees becomes more prominent. After most plants are finished blooming, and most of the fall color is gone, the garden may seem relatively bleak for winter. Only evergreen foliage remains. This is when plants that exhibit colorful bark or bare twigs really get noticed.

Various types of birch trees exhibit striking white bark all year. While the trees are bare in winter, the bark becomes even more prominent, particularly against a backdrop of evergreen trees. English walnut trees are not as striking, but are more sculptural. Fig trees (fruiting types) are more gray than white, so are more reliant on a backdrop of rich evergreen foliage or a darkly painted wall for contrast; but they grow fast enough to become interesting sculptural specimens within a few years. 

Bright white or light gray bark are certainly no substitute for the colors of flowers or foliage, but are striking nonetheless. They exploit the starkness of winter, and the sculptural nature of bare trunks and limbs.

Even without the sculptural structure of birch, walnut or fig trees, the more colorful twiggy growth of coral bark Japanese maple and osier dogwood trees can be quite an advantage in a stark winter landscape. As the name implies, coral bark Japanese maple has pinkish orange twigs. Osier dogwood can be ruddy brown, brownish orange or pale yellow. Frost improves color.

Unlike other Japanese maples that get pruned only lightly to enhance their form, coral bark Japanese maple can get pruned rather harshly just prior to spring growth in order to promote an abundance of the twiggy growth that is so colorful in winter. Osier dogwoods can get pruned down almost to the ground at the end of winter to eliminate tired older stems and promote colorful new stems for the following winter. They lack the colorful bloom that flowering dogwoods provide; so it is no bother that such harsh pruning prevents them from blooming.

Like trees with white or gray stems, coral bark Japanese maples and osier dogwoods are more striking against a backdrop of rich green foliage. Because winters are so mild here, they should be located where they will be most exposed to chill.

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Himalayan Birch

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The white bark of Himalayan birch is even more striking that that of European white birch.

Himalayan birch, Betula utilis ‘Jacquemontii’, must not be confused with the more traditional European white birch! If young trees get added to established groves of European white birch, they will never fit in. Their trunks stand vertically rather than lean casually. Their limbs are upright and angular instead of softly pendulous. Their bark is actually whiter.

Mature trees can get taller than thirty feet without getting much more than half as broad, and are relatively symmetrical for birches. The form of any single exposed tree is generally conical, although several trees together adapt to develop as picturesque groves with fewer interior limbs. The shade below is not too dark for lawn or moderately shade tolerant plants.

Maintenance is not exactly minimal. Vigorous young trees should be pruned and groomed annually, or at least every few years. Pruning should not be done in early spring when sap is likely to bleed from pruning wounds. Roots want to be watered somewhat regularly, even through the drought. When they fall in autumn, the two inch long leaves can be difficult to rake from fine gravel or bark.

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Some Trees Are All Bark

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California sycamore bark is very distinctive.

Flowers provide color and texture. So does foliage. What is less often considered is that the bark of many trees and large shrubbery can be aesthetically appealing as well. Bark is usually thought of merely as something to cover up the trunks and limbs of the plants that provide all the colorful and textural flowers and foliage.

Coral bark Japanese maple and red twig dogwood (and yellow cultivars, which are  selectively bred varieties) turn color as they defoliate for winter. However, the color is limited to the twigs and smaller stems. Red twig dogwood often gets cut back at the end of winter so that it will produce more twigs for the following winter. Mature stems and trunks are not as interesting.

Palms and yuccas do not actually have bark, but are still texturally interesting. Giant yucca trunks are weirdly sculptural. Mexican fan palm can be  ‘shaven’ to expose lean trunks with a finely textured exterior, but are more often adorned with the intricately patterned thatch of old petiole bases (leaf stalks). Windmill palm is uniquely shaggy with coarse fiber.

Arbutus ‘Marina’ is a madrone that was developed for home gardens. It is compact and symmetrical, with finely textured flaking bark that reveals strikingly smooth cinnamon-colored bark beneath. Larger manzanitas can be pruned up to expose similar bark on a smaller scale. Smooth Arizona cypress looks much like other cypresses, but with strangely  smooth bark on vigorous stems.

The bark of almost all eucalypti is interesting for one reason or another. Even the notorious blue gum, which  gives other eucalypti a bad reputation, peels away in very long strips to reveal smooth bark that fades from green to pink to tan to gray before peeling away to start the process over again. Some eucalypti have blotched bark. Red ironbark has rich brown bark that is uniformly furrowed.

Lemon gum (eucalyptus) and various birches have strikingly white bark. Lemon gum bark is smooth. Birch bark peels away like paper. Because the trees are so slender, they can be planted in groups so that there are more trunks to display the distinctive bark. These are only a few of the many trees that can impress with mere bark.

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Six on Saturday: Bark

 

Rhody said, “Cornus florida bark is rough.” He likely intended to say, “Dog would bark, ‘ruff!’.”

This is not about Rhody though. It is about these six pictures of bark of some of the more significant trees that I work with. All are native here. Only the sycamore was installed intentionally into a landscape. All of the others grew wild. There are so many interesting trees here that it was not easy to limit these pictures to just six. I actually took more pictures that were omitted.

Furthermore, a picture of Rhody is not included.

1. Platanus racemosa – California sycamore is bigger and bolder than other American sycamore. Trunks of mature trees are massive and gnarled, with this distinctively blotchy gray bark.P00613-1

2. Pinus ponderosa – Ponderosa pine is the grandest of pines. The massive trunks seem to be comparable to those of Douglas fir. Bark often flakes in bits that resemble jigsaw puzzle pieces.P00613-2

3. Quercus agrifolia – Coast live oak is second only to valley oak in regard to grandeur. Unlike valley oak, it is evergreen. Smooth gray young bark eventually becomes darker and furrowed.P00613-3

4. Pseudotsuga menziesii – Douglas fir is the majestic State Tree of Oregon, and a main timber crop there. Locally, it mixes with various ecosystems. Corky bark is rather finely furrowed.P00613-4

5. Acer macrophyllum – Bigleaf maple is the most imposing maple of the West. As the name implies, the leaves are bigger than those of any other maple. Bark gets sort of checked with age.P00613-5

6. Sequoia sempervirens – Coastal redwood is the grandest of all, and it happens to be the tallest tree in the World. Also, it is the state tree of California. The ruddy bark is distinctly fibrous.P00613-6

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

https://thepropagatorblog.wordpress.com/2017/09/18/six-on-saturday-a-participant-guide/

Post Script: For the first time, I am violating the recommended limit of six pictures to include this extra (but unnumbered) picture of Rhody for those who would be otherwise disappointed.P00613-7

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Redtwig Dogwood

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Colorful bark for the wintry landscape.

Most dogwoods are popular for spectacular white or pink spring bloom prior to foliation. Redtwig dogwood, Cornus sericea, is an odd one though. It is a ‘dog’wood that is appropriately grown for colorful twig ‘bark’. It blooms later than other dogwoods, and after foliation. The one to two inch wide trusses of tiny pale white flowers lack the flashy bracts that make other dogwoods so colorful.

Another difference is that, unlike more familiar dogwoods, redtwig dogwood naturally grows as a shrubby riparian thicket rather than as a small tree. Long limber branches can grow to more than fifteen feet high only by leaning into other trees or shrubbery. In home gardens, they typically get coppiced or pollarded just before foliating in spring, to develop twiggy growth for color next winter.

After a bit of autumn chill and defoliation, young stems of well exposed wild redtwig dogwood are a delightful glossy ruddy brown. Twigs of garden varieties are richer cinnamon red, rusty orange, soft yellow, orange blushed pale yellow, or yellowish green. Color is subdued by shade. Some cultivars have variegated foliage. Autumnal foliar color is more impressive in more severe climates.

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European White Birch

91127Like a flower girl scatters rose petals ahead of a wedding procession, European white birch, Betula pendula, tosses its small deltoid leaves soon after turning soft yellow with autumn chill. Color may not last long on the trees, but becomes a delightful mess for those who appreciate such assets. The primary allure though, is the slender strikingly white trunks, accented with black furrowing.

European white birch is very informal, but also elegant enough for formal landscapes. To best display their gently leaning white trunks, they are popularly planted in relaxed groups. Their canopies are neither broad nor dense, so a few fit together nicely. As lower branches get pruned away, pendulous upper branches sway softly in the breeze. Mature trees are mostly less than fifty feet tall.

Himalayan birch, Betula utilis or Betula jacquemontii, which has become more popular than European white birch since the 1990s, has a completely different personality. Its strictly vertical trunks and upright growth are appealing separately, but incompatible with European white birch. When adding trees to an established grove of any birch, it is very important to procure more of the same.

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Exfoliating Bark

P90720KBecause redwoods live for centuries, their bark gets very thick. They do not shed their bark as they grow. Old giant redwoods in the Sierra Nevada have bark that is a few feet thick and thousands of years old. Their bark is thicker than the trunks of what most of us consider to be large trees! Even much younger coastal redwoods that have regenerated here since clear cut harvesting about a century ago have bark that is a few inches thick.
They like their bark thick. It is the insulation that protects them from forest fires that incinerate other vegetation. Unlike most species here that are designed to burn and then regenerate more vigorously after fire, redwoods prefer to survive fire by being less combustible. As they mature, and their bark gets thicker, they become more resilient to fire. There are only a few species here that survive fire mostly intact, rather than regenerate after it.
Of course, survival is more complicated than mere thick bark. Redwoods, particularly coastal redwoods, also try to exclude other more combustible species from their forests. Also, they tend to shed lower limbs that would be more combustible during a fire, and prioritize higher and therefore less combustible canopies. Redwoods have developed a rather ingenious (but unfortunately ecologically delicate) systems of survival techniques.
Other trees are not so easy to figure out. Many species of Eucalyptus shed lower growth as if they want to be less combustible. They shed copious amounts of foliage and bark to inhibit undergrowth and other combustible vegetation. However, not only are they innately very combustible, but because they shed so much of their bark, they lack insulation from fire. It is as if they expect to burn back to the ground, and then regenerate after a fire.
Regardless of their logic, exfoliating bark of the larger eucalypti can be annoyingly messy. Exfoliating bark of some of the smaller eucalypti can be rather appealing in home gardens. This tree happens to be the same featured last week in ‘Silver‘.P90720K+