Climate 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.
Well, 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.
Like 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.
It 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.
Sweetgum, 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.
Several native species and varieties of poplar are known collectively as cottonwood. Not many are actually planted. They just have a sneaky way of appearing in well watered parts of the garden that are as damp as the riparian areas that they naturally inhabit. Only Fremont cottonwood, Populus fremontii, gets planted, rarely, and only in big spaces that can accommodate its grand scale.
Although too big and too thirsty for most refined landscapes, cottonwoods work well for shade or erosion control in big parks. However, they need to be in a lawn or irrigated landscape if they are not close enough to riparian areas to disperse their roots into soil that is somewhat moist through most of the year. Even in riparian situations, young trees need irrigation until their roots disperse.
Cottonwoods grow fast and big, with aggressive and potentially destructive roots. They should not be planted too close to pavement or septic systems. Vigorous trees might sometimes need to be pruned to reduce excessive weight. Big trees might grow to nearly a hundred feet tall, with wide canopies. Bark is handsomely furrowed with age. The deciduous foliage turns yellow in autumn.
This ain’t no ordinary maple. Although there are other maples with trifoliate leaves (divided into three distinct palmately arranged leaflets), box elder, Acer negundo, is the only maple with pinnately compound leaves (divided into three or more distinct leaflets that are arranged pinnately on a central rachis). Leaflets might be solitary too. Almost all other maples have palmately lobed leaves.
Box elder is considered to be the ‘trashy’ maple. It grows fast, but only lives for about half a century. The happiest barely get to be twice as old. Because it gets more than forty feet tall, possibly with multiple trunks wider than two feet, it can become quite a big mess as it deteriorates and drops limbs. Yet, it is aggressive enough to have naturalized in many regions where it is not native.
Despite all this, and the lack of good foliar color where autumn weather is mild, a few cultivars of box elder have been developed for landscape use. ‘Flamingo’, which is likely the most popular, is variegated with white through summer, after pink new growth fades. ‘Violaceum’ develops smoky bluish growth in spring. ‘Auratum’ starts out yellowish. Mature leaflets are about three inches long.
It may not be the biggest or best deciduous shade tree, but European white birch, Betula pendula, is famous for tall and elegant white trunks with wispy pendulous stems. It is a very informal tree that typically leans in one way or another, but is somehow right at home in refined landscapes. It is rarely alone, since it is usually planted with two or more friends, and sometimes in groves.
Not many of the biggest European white birch trees are more than fifty feet tall locally. (They can get bigger in cooler climates.) The slender trunks do not get much more than a foot and a half wide. As trees mature, the smooth white bark develops rough black furrows. The small triangular leaves turn soft yellow in autumn. The somewhat sparse foliage makes only moderate shade.
‘Laciniata’ has lacy lobed leaves, and stands straighter and narrower. ‘Youngii’ is so pendulous that it can barely stand up without staking.
The most popular hardwood in California is essentially unavailable in nurseries. California black oak, Quercus kelloggii, provides between a quarter and a third of the hardwood timber harvested in California. One would not know it by its sporadic appearance within mixed forests of the Coastal Ranges. It is much more common in the Sierra Nevada, which might be why no one grows it.
Mature trees can top out at thirty feet with broad canopies if well exposed, or might be more than seventy feet tall and relatively slender if they must compete with other trees. The biggest trees are more than a hundred feet tall. The sculptural trunks are usually less then four feet wide. Trunks of old trees are commonly rotten inside. Gray and smooth young bark gets rough and dark with age.
The distinctively lobed deciduous leaves of California black oak are not much more than four inches long. They can get nearly twice as long on the most vigorous growth, or where shaded. The dark green foliage will slowly turn brown or yellow through autumn, and then defoliate through winter. It can turn a brighter yellow or orange, but then defoliates faster, if the weather gets cool fast.
Now that they have been so popular for so long, the deficiencies of flowering pear, Pyrus calleryana, (which is also known as Callery pear), are becoming increasingly evident. The dense branch structure and compact form that are so appealing while trees are young compromise structural integrity as trees mature. Symmetrical trees can be severely disfigured if limbs get broken by wind.
In the past, flowering pear had been quite resistant to disease and insect infestation. However, now that there are so many of them within minimal proximity of each other, it is nearly impossible to avoid infection with fire blight. To make matters worse, they share this very contagious bacterial disease with fruiting pear, evergreen pear (fruitless) and apple (fruiting and flowering crabapple).
Otherwise, healthy and well structured trees provide some of the best autumn color for mild climates. Foliage that was rich green through summer becomes bright yellow and orange on a weak season, with more bright red and burgundy with a good chill. The white spring bloom is likewise more colorfully profuse after a colder winter, although some find the fragrance to be objectionable.