It is the ‘ivy’ of ivy league schools. Nonetheless, Boston ivy, Parthenocissus tricuspidata, is neither an ivy, nor indigenous to Boston. It is from eastern Asia, and is related to grape vines. It is related to Virginia creeper too, which is actually native to Boston, Virginia and the eastern half of North America. It has become popular locally for freeway sound walls.
Boston ivy is an aggressive clinging vine that can climb to the top of a ten story building. Unfortunately, there are a few problems with that. It ruins wooden or painted surfaces, so can only climb concrete or masonry. It climbs over windows if it gets the chance. Thicket growth is difficult to remove if it is too high to reach. On rare occasion, mice can nest in it.
Otherwise, Boston ivy works well on freeways. Although deciduous, its vines discourage graffiti. Even while bare, its texture helps to muffle sound. Its exquisite autumn foliar color might begin to develop as early as late summer, and lingers until frost. Boston ivy is quite resilient to neglect. Shabby plants generate fresh new growth after major winter pruning.
After reading so much about the exquisite foliar color that most everyone else in the Northern Hemisphere gets this time of year, I must admit, I can get rather envious of those who experience four seasons instead of just two. The abundance of spring in the Southern Hemisphere does not help. Why have I not found a garden blog from Ecuador or Indonesia so that I have something to point and laugh at? It just isn’t fair.
Well, now I have something to brag about.
I found this bright red leaf on a crepe myrtle in town. Isn’t it pretty? Go ahead, you can tell me. It is gorgeous, RIGHT? Go on; say it! Say it NOW! LOUDER!
Soon, all the foliage behind it will be turning red and orange with maybe a bit of yellow. Can you see it? I think some of those leaves are starting to consider…
It is a hybrid. It is naturally occurring. Yet, most cultivars (garden varieties) resulted from intentional hybridization and selection. It is not as strange as it seems. Freeman maple, Acer X freemanii, is a naturally occurring hybrid of silver maple and red maple. It grows wild where the natural ranges of the parents overlap. From their example, breeders learned to selectively breed the cultivars.
These cultivars combine the fast growth rate of silver maple with the structural integrity of red maple. None get to be as imposing as the silver maple. Some get to be about forty feet tall and wide, which is a bit bigger than red maple gets in local climates. Foliage is lacy like that of silver maple, but more substantial, like that of red maple. It develops brilliant orange and red color for autumn.
Freeman maple, although locally uncommon, is one of the more practical maples here. Like silver maple, it does not require much chill in winter. Like red maple, it develops a symmetrical canopy with reasonably high branches. Roots should be complaisant with concrete. Because it is a hybrid, it is mostly sterile. It does not produce enough seed to be invasive in more conducive climates.
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.
Autumn does not get cool enough locally to prevent everything from blooming. A few plants can bloom sporadically all year except only during the coolest part of winter. A few plants naturally bloom in autumn. Cool season annuals begin blooming before warm season annuals finish. Flowers can potentially provide plenty of autumn color if necessary. A mild climate can be a major advantage.
It can also be a disadvantage. Minimal chill causes deciduous foliage to start to get messy before it starts to get colorful. Some deciduous plants shed completely before getting chilled enough to develop appealing autumn color. A few others do not even get cool enough to defoliate completely. They instead retain their shabby old foliage through winter until new foliage replaces it in spring.
Nonetheless, several adaptable deciduous plants get sufficient chill to develop impressive autumn color here.
Sweetgum, Chinese pistache, flowering pear and ginkgo are likely the four best deciduous trees for autumn color locally. Sweetgum and Chinese pistache produce the most impressive ranges of vibrant colors. Flowering pear is comparable, but with less yellow, and more rich deep burgundy red. Ginkgo lacks such range of color, but develops the brightest and clearest yellow autumn color.
Boston ivy, crape myrtle and persimmon get about as colorful as sweetgum, even if incidentally to their primary duties. Crape myrtle is popular for its abundant and richly colorful bloom in summer. Persimmon is a fruit tree. Boston ivy obscures graffiti and helps muffle sound on freeway soundwalls. Cottonwood and black walnut turn bright yellow, but in the wild rather than in refined gardens.
Even for the locally mild climate, there are plenty of deciduous plants that provide foliar autumn color. Trees are the most familiar. Vines and shrubbery are also popular. Because this mild climate is marginal for some of them, color is likely to be variable from year to year. Unfortunately, some that perform satisfactorily for inland locations may perform less satisfactorily in coastal conditions.
Autumn color is different every year. Sometimes, early and sudden cool weather after a mild summer promotes good foliar color that lingers longer while relaxed trees slowly realize that they should probably start to defoliate. Sometimes, early wind and rain accelerate defoliation of otherwise good color. There are a few variables that trees must adapt their performance to.
Warm and arid weather two weeks ago started the process of defoliation suddenly and a maybe slightly early this year. Even before the weather gets cool, deciduous trees are already starting to shed the oldest of their foliage that they do not need in order to hold their youngest foliage a bit later into autumn. Evergreen trees do the same to limit desiccation.
Slightly breezy weather that was so pleasant after such heat was just enough to start dislodging deteriorating foliage. Now, leaves are already starting to fall before they develop much color. Redwoods and pines are likewise dropping browned needles. Fortunately, trees that are the most colorful in autumn tend to hold their foliage better until the weather gets cooler.
It is impossible to predict how colorful trees will be this autumn; although if storms are as healthy as predicted, the mild temperatures may inhibit color, while wind and rain dislodge colorful foliage. Regardless, it is already time to start raking falling leaves and needles. They can get messy, and when the rain starts, they can stain pavement and clog gutters.
When more foliage falls later in autumn, it will need to be raked from ground cover, surviving portions of lawn, and any other plants that collect it, so that it does not shade out the sunlight.
Mild climates allow more flowers to bloom through autumn and winter here than in most other parts of America. That is why cool season annuals like pansies and violas are so popular. Cyclamen can be planted now too. None will be obscured by snow. By the time cool season annuals start to fade, warm season annuals will be replacing them. There is something to bloom in every season.
There are a few disadvantages to mild climates, though. Many plants rely on significant winter chill to stay on schedule. Inadequate chill limits the cultivars of apples and pears that are productive here. Not many spring bulbs will naturalize. Prior to winter, some deciduous plants are hesitant to resign to dormancy until they experience a chill that is cool enough to convince them it is autumn.
Some deciduous plants recognize a specific temperature as credible evidence of a change of seasons. Others want a specific temperature to be sustained for a specific duration or repeated for a few nights. Shorter days and longer nights are taken into consideration by species who want to confirm what they deduce from the weather. Different plants use different methods of observation.
That is why deciduous plants who develop foliar color before defoliating in autumn do so on their own terms. Weather conditions that promote excellent color among birches may not be the same that cause flowering cherries to color well. Warmth and minimal humidity that sometimes prompt premature and blandly colored defoliation of sycamores might enhance later color of sweetgums.
Sweetgum, Chinese pistache, flowering pear and ginkgo are the most reliable trees for foliar color in autumn. Ginkgo turns only brilliant yellow. The others exhibit an excellent mix of yellow, orange and red. Crape myrtle can be about as colorful, but is not always as reliable.
Of course, there is more to these and other deciduous trees than their colorful foliage in autumn. After all, they are trees. Their particular characteristics and appropriateness must be considered before adding any of them to a landscape.
Autumn is not much to brag about here. It supposedly got just cool enough at night for the minimal requirement of frost, at 32 degrees, but no one noticed. It has been getting to the low 80s during the day. There has been no rain yet, and none is in the forecast. As bland as such weather seems, it is not at all out of the ordinary. Autumn often arrives later than it does elsewhere.
Consequently, autumn foliar color is not much to brag about either. There are only a few trees that reliably develop good color, such as sweetgum, pistache, flowering pear, crape myrtle and maidenhair tree (ginkgo). As reliable as it is, maidenhair tree provides only bright yellow, without the oranges and reds that the others exhibit. None are exhibiting significant color just yet.
There are several other trees that have potential to develop good color, but are not as reliable about doing so. Birch can get almost as brilliant yellow as maidenhair tree does, but does not do it every year. Red oak may turn brilliant orange with a bit of brownish red mixed in, but only every few years or so. On rare occasion, even London plane (sycamore) shows off burnt orange.
Every species has a distinct personality. They each respond differently to different variables. Weather conditions that stimulate good color among flowering cherries may not stimulate good color for bigleaf maples. Dogwoods that colored so well at about the same time last year as the tulip trees, are already nearly bare after minimal color, while the tulip trees are mostly green.
Every few years, if mildly but suddenly chilled, these cottonwood develop a brighter yellow, with less blotching. With slower and drier chill this year, they are deteriorating and falling without much yellow at all.
Now that leaves are falling, they need to be raked. Large leaves, like those of sycamore and fruitless mulberry, can shade out lawn, shallow ground cover or dense shrubbery. If shade is not a problem right away, mildew can be after only a bit of rain. If abundant enough, finely textured silk tree or jacaranda foliage that typically sifts harmlessly through shrubbery and most ground cover, can accumulate and damage lawn, dichondra and the densest of ground cover. Walnut foliage has an herbicidal effect on sensitive annuals and some perennials.
Foliage is only beginning to fall. Cooling weather causes deciduous trees to shed more. Rain and wind bring the foliage down even faster. Even evergreen trees that naturally shed throughout the year will likely shed more through the upcoming wintry weather. Some trees start to defoliate early in autumn. Some hold their foliage until frost. Some trees that seem to be evergreen hold their foliage through winter, and then only drop their older foliage as it gets replaced by new foliage as winter ends.
Pavement and decks should be raked of leaves, not only to avoid staining, but also because rotting leaves can become dangerously slippery. Curbside gutters are too visible to get neglected for too long. However, heavy rain can quickly deliver to the cleanest of gutters a mess of fallen leaves as well as any other debris and litter that happens to be up the road. Strong wind can be filtered through hedges, leaving drifts of blowing leaves.
Leaves should also be cleared from roof gutters and downspouts, and may need to be cleared away again later in the season. More debris may need to be removed from awkward spots where it might accumulate, such as behind chimneys. Flat roofs may need to be raked.
There are a few exceptions to the need to rake fallen leaves. Where they get absorbed into coarse ground cover like Algerian ivy, falling leaves are generally not a problem. Pine needles and cypress foliage can be left if it happens to be useful for the natural suppression of weeds. Mature coast live oaks and valley oaks that are accustomed to a layer of their own fallen leaves over the surface of the soil actually want it to stay. For them, the foliar debris is a mulch that adds organic matter, insulates the soil, and retains moisture.
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.