Shade Trees Adapt To Urbanism

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Traditional shade trees get quite large.

Modern urban home gardens are shadier and more confined than older suburban home gardens originally were. Modern homes are both taller and closer together on smaller parcels. Fences are also taller to compensate for the minimal proximity of adjacent homes. Less sunlight reaches the ground. There is not as much space available for shade trees. Nor is there as much use for them.

Huddled modern homes are simply not as exposed to sunlight as older suburban homes were. Sunlight is more of an asset than a liability. Walls, ceilings and windows are so thoroughly insulated that shade is less important. Solar arrays up on roofs must remain exposed to sunlight. Smaller and denser trees are more important for obscuring views of adjacent homes, rather than for shade.

Shade trees are still useful for rural and suburban homes. Shade helps to keep older and less energy efficient homes cooler through warmer summer weather. If strategically situated to the south, west or southwest, they shade homes during the warmest time of day. Well proportioned trees do not darken too much of their gardens. Deciduous trees allow warming sunlight in through winter.

The popularity of modern urban homes is directly proportionate to the popularity of small evergreen trees. Such trees fit into smaller garden spaces, and permanently obscure unwanted scenery. Big deciduous shade trees that are practical for larger garden spaces become obtrusive in confined spaces. Defoliation in winter reveals unwanted views, and deprives the landscape of privacy.

Some of the more practical of small evergreen trees are actually large shrubbery. English laurel, Carolina cherry, photinia, hopseed bush and various pittosporums can get high enough to obscure neighboring windows. All are conducive to pruning if they get too tall. If staked on single straight trunks, or pruned to expose a few sculptural trunks, they do not occupy much space at ground level.

Tristania laurina, and some melaleucas are naturally small to midsized evergreen shade trees. Some species of Podocarpus can be pruned as midsized trees.

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.

Bigleaf Maple

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A maple with unusually big leaves.

Its natural coastal range extends from the extreme southern corner of Alaska to the southwestern corner of California. Another inland range occupies foothills of the Sierra Nevada. Bigleaf maple, Acer macrophyllum, is the most common and prominent native maple here. However, it prefers the seclusion of forested riparian situations at higher elevations locally. It is rare in urban gardens.

Bigleaf maple is best in the wild anyway. It dislikes the aridity of most of the urban and suburban areas of California. (San Jose is in a chaparral climate. Los Angeles is in a desert climate.) Roots of bigleaf maple are potentially aggressive, especially if irrigated generously. They easily displace pavement. Nonetheless, where climate and circumstances allow, bigleaf maple is a grand tree.

Wild trees grow as tall as a hundred fifty feet within forests where they compete for sunlight. Well exposed suburban trees should stay lower than forty feet, while extending their canopies broader than tall. The big and palmately lobed leaves are mostly more than six inches wide. Foliage turns yellow in autumn, and is abundant as it falls. Self sown seedlings often grow under mature trees.

Pin Oak

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Pin oak is not drought tolerant.

There are several oaks, especially natives, that do not need much more water than they get from rain. Pin oak, Quercus palustris, is not one of them. It is naturally endemic to areas that are damp or swampy for part of the year. It is more tolerant than others are to lawn irrigation, but is also more sensitive to drought.

Compared to other oaks, pin oak grows fast while young. It can get two stories tall in about ten years. Then, it takes more than twice as long to double in size. Old trees do not get much more than fifty feet tall, with trunks nearly three feet wide.

The deciduous foliage turns as brown as a grocery bag in autumn, and may linger late into winter, or until it gets replaced by new foliage in spring. The distinctively deeply lobed leaves are about two to five inches long, and about two thirds as wide. Each leaf has five or seven lobes. Each lobe has five to seven teeth.

Evergreen Trees Have Their Place

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Evergreens are sometimes the best choice.

Deciduous trees that were bare all winter are now foliating and making shade. They sure will be appreciated when the weather gets warmer through summer. They will defoliate next autumn, in time to let warming sunlight through while winter is cool. Their lifestyles are naturally compatible with those of the people who live with them. They really have the system down.

Evergreen trees are good at what they do as well. They obscure unwanted views and provide privacy all year. If given adequate space and located far enough away from the home and neighboring homes, their shade should not be a problem. Like any other feature in the landscape, properly selected and strategically placed evergreens are quite functional.

There are certainly more to evergreen trees than the coniferous (cone-bearing) evergreens like pine, spruce, cypress, cedar and juniper. Any tree that retains foliage throughout the year is evergreen, including camphor, Southern magnolia, carob, California pepper, coast live oak, fern pine, all palms and all eucalypti, just to name a few. There are really too many to list.

Larger modern homes on smaller parcels are a bit more challenging to evergreen trees than more traditional homes that have more space around them. Average fences do not maintain privacy for upstairs windows that are too close to neighboring homes. However, there is less space and sunlight for trees, and additional shade can be a bother for lower windows.

It seems that smaller trees are often the best fit for bigger homes. Sometimes, a large evergreen shrub, like one of the various pittosporums, can do the job of an evergreen tree, but fits better where space is limited. As silly and passe as they seem to be, Italian cypress are narrow enough to fit into tight spots, at least until they get too big.

Contrary to popular belief, most evergreen trees are messier than most deciduous trees. They drop only minor volumes of foliage, but they do so throughout the year. Deciduous plants drop most or all of their foliage within a limited time about autumn. Only those that drop flowers, fruit or both in spring and summer are messier than evergreens.

Larch

41217Climate is why the European larch, Larix decidua, is so rare here. It prefers cooler weather in both winter and summer, and more humidity. Foliage can roast if too exposed through summer. Small trees that are partly sheltered or partly shaded by larger trees have the best color and foliar density. Larch are innately reliant on somewhat regular watering, so are not drought tolerant. The mildly cool weather of autumn is enough to brown the formerly bluish foliage, which falls shortly afterward.

In the wild, larch trees can get as tall as other big coniferous trees. However, the many different garden varieties stay much smaller. Some are very pendulous. A few have contorted stems. Of the few that can sometimes be seen locally, most are compact dwarfs that grow more like low and dense shrubbery than trees. Some get only two or three feet tall and broad, and grow very slowly. These can stay in containers or planters for many years.

Deciduous Evergreens

P91201Well, that is certainly a contradiction of terms. One might say it is an oxymoron. Decades ago, it really was how we classified what we now know more simply as ‘deciduous conifers’. There are not many of them. Ginkgo is a gymnosperm like conifers are, but is not really a conifer. Otherwise, there are only five other types of deciduous conifers, which defoliate through winter.

Laryx is a genus of about a dozen species that are known collectively as larch. Taxodium includes two species known as bald cypress, as well as a third evergreen species. Pseudolaryx amabilis, known as golden larch, Glyptostrobus pensilis, known as Chinese swamp cypress, and Metasequoia glyptostroboides, known as dawn redwood, are all three monospecific genera.

Some species of larch are common within their respective natural ranges. So are the bald cypresses. The others are quite rare. However, dawn redwood became a fad decades ago, so is not so rare in landscape situations. To those of us who expect all conifers to be evergreen, deciduous conifers seem to die suddenly in autumn. To some, it is not exactly a desirable characteristic.

The dawn redwood above lives in our landscapes. The tall evergreen trees behind it are native coastal redwood. Obscured by the yellowing birch to the right, a small giant redwood (another oxymoron) represents the third and only other species of redwood. The fall color of this dawn redwood appeals to some, but to others, it looks like one of the native redwoods abruptly died.

Our bald cypress below does not look so much like a dead redwood. The foliar texture and branch structure are quite distinct. The cinnamon brown fall color is actually rather appealing.

Of course, these pictures are nearly two weeks old. By now, both trees are likely bare because of the rain.P91201+

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.

Red Willow

P91108It is almost never planted in home gardens, but the native red willow, Salix laevigata, has a sneaky way of getting where it wants to be. The minute seeds go wherever the wind blows them. Because it is a riparian tree, red willow prefers well watered spots. If not detected and pulled up in the first year, it can grow rather aggressively, and overwhelm more desirable plants, although the somewhat sparse canopy makes only moderate shade.

With a bit of grooming, red willow can be a handsomely asymmetrical tree, with upright branch structure. However, even the healthiest trees rarely get more than thirty feet tall, or much more than forty years old. The leaves are a bit shorter and wider than those of the more familiar weeping willow, and do not color as well in autumn. There are actually a few other native willows that are also commonly know as red willow. Some are quite similar, while others are very different.P91108+

Color Is Lacking This Autumn

41029thumbSweetgum, flowering pear and Chinese pistache are the most reliable trees for flashy autumn foliar color, especially in such mild climates. They may not seem like it this year though. After a late start, only sweetgum is coloring well. Flowering pear trees that are beginning to show color farther inland seem to lack their typical bright yellow and orange, and are showing more dark rusty red.

Like so many flowers that bloom in spring, foliar color in autumn is as variable as the weather. Temperature and humidity can either inhibit or enhance color. It is impossible to say what caused the disappointing color so far, or if foliage that colors later will be just as bland. A sudden chill could change things for Chinese pistache that are still behind schedule.

Maidenhair tree (gingko) is the best for bright yellow, but lacks any other color. Fruitless mulberry, tulip tree and various poplars can be nearly as bright yellow in a good season, and may still color well. Of the various willows, only a few color well, and they tend to be more sensitive to weather. Early rain can rot their leaves before they get much color at all.

Although elms are not known for coloring, some of the modern varieties turn remarkably bright orange. However, the few oaks that color well in colder climates turn only dingy brown locally. The few North American maples that can provide color do not hold their colored foliage very long. All sorts of trees have all sorts of personalities.

Eastern redbud, smoke tree and crape myrtle are shrubs or small trees that color as well as larger trees in autumn. Crape myrtle can be as bright yellow, orange and red as sweetgum. Some Japanese maples color better than others, and some can be quite impressive, but only if their foliage does not get roasted by warm and arid weather through summer.

Where it can be accommodated, Boston ivy is an aggressively clinging vine that provides all the remarkably colorful foliage on freeway sound-walls. It is out on the freeways for a reason though. It can ruin any other surface that it clings to.