Since the Dutch Elm Disease (DED) epidemic that killed so many old and stately American elm trees so many years ago, the old fashioned Chinese elm, Ulmus parvifolia, has been unavailable in nurseries. That is why there are only old and middle aged trees, and maybe a few feral seed grown trees. Chinese elm is not bothered much by the disease, but is a vector. ‘Drake’ is a modern DED resistant cultivar, but it has a very different personality, with a more upright and symmetrical structure.
The elegantly lanky trunk and main limbs can be quite curvacious, with distinctively blotched gray and tan bark. The deciduous foliage can be messy in autumn as it falls slowly and may linger through December. The neatly serrate leaves are only about an inch or two long, and half as wide. Mature trees can be more than fifty feet tall.
Chaparral climates are not easy without irrigation. The long summers are warm and arid. California buckeye, Aesculus californica, knows what to do if it can not stay hydrated out in the wild. It simply defoliates. Yes, it goes bare right in the middle of summer. If it does it early enough, it refoliates after rain resumes in autumn, only to defoliate again for winter.
This ‘twice deciduous’ characteristic is likely why California buckeye is not more popular for unirrigated landscapes of other natives. Shade is an asset through warm summers. In coastal, riparian or irrigated landscapes, the original spring foliage lasts through summer to defoliate in autumn, like that of most other deciduous plants. It may get shabby though.
Nonetheless, California buckeye is a delightful small tree, typically with a broad and low canopy suspended by a sculptural branch structure. Not many get more than twenty feet tall, although some get twice as tall. Bark is strikingly pallid gray. The elegant leaves are palmately compound. Six inch long trusses of tiny white flowers are sweetly fragrant in spring.
No other maple is native to so much of North America as the common box elder, Acer negundo. Yet, because of innate structural deficiency and a general lack of pizazz, it is also one of the least popular. The smaller and more adaptable garden varieties are more often grown for their interestingly colorful foliage. ‘Flamingo’ starts out with pink, white and pale green foliage that turns richer green and white by summer. ‘Violaceum’ has smokey purplish new foliage that fades to rich green. ‘Auratum’ has yellowish foliage that fades to chartreuse green. Any stems that try to revert to a more natural shade of green should be removed before they dominate. Unlike other maples that have distinctively palmate leaves, box elder has compound leaves with three or more leaflets each.
Spring seems to develop suddenly, and without a very precise schedule. Star magnolia, Magnolia stellata, which can bloom as late as early in April, is already finished blooming in most regions. It should be no surprise. Technically, it can bloom before March. Foliage does not compete with bloom on otherwise bare stems. It appears as bloom deteriorates.
The bright white flowers are about three inches wide, and lavishly profuse. Cultivars with pale pink bloom are increasingly popular. Their pink color may be variable, according to the weather. Flowers have more than a dozen narrow tepals. Some are fluffier with twice as many. Fragrance is mild. Stems can be cut and brought inside just as buds pop open.
Star magnolia is more of a deciduous flowering shrub than a small tree. It should not get much taller than six feet, although it can eventually get to be nearly twice as wide. Partly shaded specimens can reach ground floor eaves. The lime green leaves darken through summer, turn pale yellow for autumn, and finally defoliate to reveal sculptural gray stems.
Japanese maples get all the notoriety. They have such delightful texture and form. Many are proportionate to small spaces, such as atriums. Realistically though, they are overrated and overused. Meanwhile, other maples that work as larger shade trees remain obscure. Norway maple, Acer platanoides, gets broad enough to shade much of an urban garden, but rarely gets to forty feet tall.
Of course, Norway maple has innate limitations. It dislikes arid and harshly warm desert climates. Nor does it like to be too close to the coast. Los Angeles is about as far south as it wants to live. In the Pacific Northwest, it gets much bigger, and develops greedy roots. The non-cultivar species is invasive there. Norway maple defoliates neatly for winter, but then refoliates late in about April.
Almost all local Norway maples are cultivars. ‘Schwedleri’ has richly bronzed foliage. It is rare now, but was a popular street tree in the 1950s. ‘Crimson King’ has richer purplish foliage, but is less vigorous. ‘Drummondii’ displays delightful variegation. The deciduous foliage of Norway maple turns soft brownish yellow or gold for autumn. The palmately lobed leaves may be five inches wide.
Flowering dogwood, Cornus florida has something in common with Poinsettia. The most colorful component of their bloom is not floral, but is instead foliar. What appears to be petals are colorful leaves known as bracts. Exactly four bracts surround each small cluster of tiny and unimpressive pale green real flowers. These bracts are most popularly white, but can be pink or rarely brick red.
The deciduous trees are bare now, but bloom spectacularly in early spring. Any necessary pruning should happen after bloom, and preferable after new foliage matures somewhat. Floral buds for next year are already prominent on the tips of bare twigs. Dormant pruning would eliminate some of the buds prior to bloom. For now, only minor grooming of unbudded interior growth is practical.
Mature flowering dogwood trees can be twenty feet tall, but typically stay lower. As understory trees, they prefer a bit of shelter from larger trees. Foliage can scorch if too exposed. Some cultivars have variegated foliage. All can develop vibrant orange and red foliar color for autumn, even with minimal chill. Floral debris resembles fallen leaves that fall just as new and real foliage develops.
From the north end of the Sacramento Valley to the San Fernando Valley, the valley oak, Quercus lobata, is among the most familiar and distinctive of native oaks. It is the largest oak of North America, reaching more than a hundred feet tall with trunks as wide as ten feet, which is why it is rare in urban gardens. The hundred fifty foot tall ‘Henley Oak’ of Covelo is the tallest hardwood tree in North America. The oldest trees are about six centuries old.
The two or three inch long leaves have deep and round lobes. The foliage turns only dingy yellow and then brown in autumn, and can be messy as it continues to fall through early winter, particularly since the trees have such big canopies. The gnarly limbs are strikingly sculptural while bare through the rest of winter. The gray bark is evenly furrowed.
Incidentally, Oakland, Thousand Oaks, Paso Robles and various other communities within their range are named for valley oaks. (‘Roble’ is the Spanish name.)
The problem with all the colorful foliage that adorns so many of the deciduous trees in autumn is that it does not stay in the trees too long. Combined with all the other less colorful deciduous foliage, as well as whatever evergreen foliage happens to fall this time of year, it will become quite a mess by winter. Rainy and windy winter weather will only make it messier by bringing down even more foliage!
Contrary to popular belief, many evergreen trees are just as messy as deciduous trees are. Instead of dropping all their foliage in autumn or winter, most evergreens drop smaller volumes of foliage throughout the year. The mess is less obvious since it sneaks up slowly, but can accumulate over a few months. Only a few evergreen trees drop much of their foliage in more obvious seasonal phases.
Debris from evergreen trees is actually more likely to be a problem for plants below. Pines, cypresses, firs, spruces, cedars, eucalypti and many other evergreen trees produce natural herbicides that inhibit the emergence of seedlings of plants that would compete with them in the wild. In landscape situations, this unfortunately interferes with lawns, ground covers and annuals. Besides walnuts and deciduous oaks, not many deciduous trees use this tactic.
Regardless, any foliar debris can be a problem if allowed to accumulate too long. Large leaves, like those of sycamore, can accumulate and shade lawn, ground cover and some dense shrubbery, and can eventually cause mildew and rot. Finely textured foliage, like that of jacaranda or silk tree, can sift through most ground covers to the soil below, but can still make a mess on lawn.
Before rainy weather, debris should be cleaned from gutters and downspouts. Because some foliage continues to fall through winter, gutters will likely need to be cleaned again later. Flat roofs and awkward spots that collect debris, such as behind chimneys, should also be cleaned.
Gutters at the street are more visible and accessible, so do not often accumulate enough debris to be a problem, but may need to be cleaned if they become clogged with debris washed in by the earliest rains. Fallen leaves should be raked from pavement so that it does not get dangerously slippery, or stain concrete too much.
Where autumn chill is minimal, the best and brightest yellow autumn color is that of the ginkgo, Ginkgo biloba. Some know it at the maidenhair tree. Except for older trees that produce messy and stinky fruit, it is a notably clean tree. Perhaps it is too clean. It drops nothing all year, but can defoliate too soon once it develops it striking autumn color. Minimal chill actually prolongs the process.
Ginkgo is dioecious, with separate genders. Modern cultivars for landscapes are male, so produce no obnoxious fruit. Female cultivars that produce nuts and fruits are not commonly available in nurseries locally. (As objectionable as their aroma is, the nuts and fruits are edible.) Some people may be allergic to the pollen of mature male trees. Many mature trees predate modern cultivars.
Trees are somewhat slender and perhaps sparse while young. They develop a broader canopy as they age. Trees can get more than fifty feet tall, with sculpturally irregular branch structure. Foliar venation radiates outward from the petioles. Leaves, which are about two or three inches long, therefore have the shape of fishtails. Leaves on current season stems are cloven into paired lobes.
‘A Tree Grows In Brooklyn’ documents the resiliency and invasiveness of the common but typically undesirable tree of Heaven, Ailanthus altissima. Once a single female tree get established, the extremely prolific seeds get everywhere, including cracks in concrete. The resulting seedlings conquer wherever they are not dug out. If cut down, they just resprout from the roots.
Male trees smell horrible while blooming for about a month in spring or summer. They are pollinated by flies, so naturally smell like what flies like. The tiny yellowish or tan flowers hang on panicles that can be a foot and a half long. Female blooms are not as big, prolific or objectionably fragrant. However, stems, leaves and all other parts of both genders smell rotten when handled.
Tree of Heaven, which has earned the alternative names of ‘tree of Hell’, ‘stink tree’, ‘ghetto elm’ and ‘ghetto palm’, is no longer a tree that gets planted by choice. It is typically a tree that plants itself, and on rare occasion, happens to grow into a good situation. They should not be allowed to overwhelm more desirable trees, or get too close to concrete or other damageable features.
Young trees grow very fast to about forty feet tall. Older and slower trees do not get much taller, although sheltered trees can get twice as tall, with elegant gray bark. They do not live much more than fifty years. The big pinnately compound leaves are surprisingly pretty. On vigorous shoots, individual leaves can get as long as two and a half feet, with leaflets as long as six inches.