They start out simply enough, as weirdly twisted bare stems in fancy floral arrangements. By the time the last flowers fade, the submerged parts of these bare stems develop roots and perhaps leaves. These now rooted cuttings then graduate into pots or gardens. Most curly willow, Salix matsudana ‘Tortuosa’, is therefore unplanned. It is rare from nurseries.
Mature trees should not get much taller than fifteen feet, with awkwardly irregular branch structure. Regular pruning and grooming eliminates congested and structurally deficient growth. Alternatively, pollarding or coppicing during winter dormancy promotes vigorous growth. Healthy trees can drop overburdened limbs, and might live for only twenty years.
Curly willow, which is also corkscrew willow, is popular more for distinctively curly stems than as a small deciduous shade tree. Specimens that provide such stems for cutting do not need to be very big. If cut and dried while dormant during winter, stems can not grow roots in water. Nor will they require plucking to remove their leaves, which are also curly.
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.
After a forest fire, white alder, Alnus rhombifolia, might be the first trees to regenerate into freshly deforested riparian situations. It grows quickly to exploit such an opportunity, and temporarily dominate a recovering ecosystem. Individual trees do not live for much more than half a century though. Then, they relinquish area to slower but more enduring trees.
Years ago, white alders did the same in new landscapes that needed shade. They grew fast to provide shade while preferable trees matured slowly. They subordinated and then vacated their landscapes as the preferred trees grew. Unfortunately, this technique is not so practical within municipalities that require but rarely grant permits for removal of trees.
Although native, white alder is not prominent everywhere within its natural range. It might seem to be rare in Southern California, with only a few sporadic trees to provide seed for regeneration after a fire. Farther north, large and sustained colonies resist encroachment of other trees. Mature white alders can get forty to eighty feet tall, or taller where crowded by taller trees.
There are not many trees that are as reliable for strikingly bright and clear yellow autumn foliar color as the maidenhair tree, Gingko biloba, is, even in mild coastal climates. The distinctive leaves flare out like fish tails, each with a prominent cleft that divides it into two wide lobes. (The species name ‘biloba’ means ‘two lobed’.) Some cultivars lack foliar clefts, have narrower leaves, or even develop milder yellow color in autumn. Those developed for home gardens exhibit relatively symmetrical branch structure, and are exclusively male, so can not produce the stinky fruit that some older female trees drop. (Trees grown from seed can be either male or female. Female cultivars are grown for fruit production and bonsai.) Some ancient trees in Japan, Korea and China are more than a hundred feet tall. Fortunately, maidenhair tree grows slowly enough to stay proportionate to compact urban gardens for many decades.
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.
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.