This must be one of the sillier horticultural names. Tree houseleek, Aeonium arboreum, is neither a tree nor related to leeks. The biggest cultivars can not stand much more than three feet tall. Above that, their succulent foliage gets too heavy for their fleshy stems and fine roots. They perform well as houseplants only within very sunny situations.
Formerly common tree houseleek, with simple green foliage, is not so common anymore. Almost all popular modern cultivars are variegated or bronzed, with wide foliar rosettes. Variegation ranges from bright lemony yellow to creamy white. Bronze ranges from light brown to very darkly purplish. Foliar rosettes are about four to eight inches wide.
Plumply conical trusses of tiny yellow or chartreuse flowers bloom for spring. They are neither numerous nor brightly colorful, but are weirdly interesting. Fresh spring foliage is most colorful and lush. It can fade and partially shed during arid summer weather. New plants propagate very easily from dragging stems or cuttings of pruning scraps.
Foliar color is not limited to autumn. Some deciduous plants display colorful foliage from spring to autumn. Then, some of these change color for autumn. Some evergreen plants display colorful foliage through the year. Variegation of foliage can be more colorful than associated bloom. So can unvariegated bronze, purple, red, yellow, blue or gray foliage.
All sorts of plants exhibit variegation or other variations of color of their foliage. They can be annuals, perennials, shrubs, vines, trees, or houseplants. Although many are popular primarily because of their foliage, some provide appealing bloom as well. Blue and gray foliage is a natural advantage in harsh climates. Other colors are selections of mutations.
Because variegation deprives portions of foliar surface area of the chlorophyll needed to perform photosynthesis, it inhibits growth. This can be an advantage for plants that grow too vigorously otherwise. However, many variegated plants occasionally develop growth that is not variegated. If not removed, it can overwhelm and displace desired variegation.
New Zealand flax, dracaena palm (Cordyline australis), gold dust plant, euonymus, coral bells and hosta are some of the many plants that are more familiar with colored foliage or variegation than without. If simple unvariegated coleus, croton or caladium are available, they must be notably rare. Blue spruce is always blue. Purple leaf plum is always purple.
Although both gold and gray junipers are popular, the most common are green. Bronzed and variegated cannas are likewise not quite as popular as those with simple lush green foliage. Pittosporum tobira is so much more vigorous without variegation than with it, that the two distinct types of this same species perform different functions within landscapes.
Golden honeylocust supposedly produces lighter shade than darker green honeylocust. ‘Ruby Lace’, a bronze cultivar of honeylocust, supposedly produces faintly darker shade. Some golden or variegated foliage is more susceptible to scorch; although sun exposure enhances foliar color and variegation. Fresh new spring growth gets the best foliar color, but is likely to fade through summer.
Wispy billows of pinkish or tan blooms through June and July are what the smoke tree, Cotinus coggygria, is named for. It probably should have gotten more recognition for brilliant foliar color in autumn. It reliably turns bright yellow and orange, and if the weather is right, it can turn rich red and even purplish. Until then, the popular modern varieties have either dark purplish or light yellowish foliage. Some of the older plants have slightly bluish green foliage. The nearly circular leaves are about two or three inches long. Yellowish varieties tend to be shortest. Those with purplish or bronze foliage get larger. Old fashioned green plants are the largest, and can get twelve feet tall and broad. Smoke tree can be large shrubbery, or pruned up as small trees. Aggressive pruning in winter promotes better foliar color through spring and summer, but inhibits smoky bloom. Slightly distressed plants have better color in autumn. Plants that are watered too much are likely to succumb to disease within only a few years.
Flowers get all the credit for color. They certainly are the most colorful features in the garden, as well as the most fragrant. However, foliage can do so much more than simply provide green. It can be hued with yellow, red, blue, purple, bronze, gray, or variegated with white or yellow. Plants with colorful foliage can range in size and function from small annuals and perennials to shrubbery, vines and even trees.
Hydrangea, hosta, ivy, English holly and various pittosporum are some of the more popular plants for white variegation, and are often variegated with yellow. Euonymus can conversely be variegated with white, but is usually variegated with yellow. New Zealand flax can be variegated with pink, bronze, brown or gold. Box elder is a good sized deciduous tree that can be variegated with white, or alternatively frosted uniformly with gold as new foliage emerges in spring. There is even a variety that has slightly purplish or smoky colored new foliage.
Silver mountain gum, silver Mediterranean fan palm, lamb’s ears, artemesia and the various dusty millers have remarkably silvery foliage. Silver mountain gum can grow into a mid-sized tree with a stout trunk. Lamb’s ears is a low perennial. Olive trees, some junipers and the various lavenders have gray foliage. Colorado blue spruce and some agaves have striking blue color.
Various purple leaf plums and Japanese maples are famous for their purplish foliage. Smoke tree and some beech have even darker purplish foliage. Some New Zealand flax and cannas can be just as purple or comparably bronze.
Actually, New Zealand flax and cannas, as well as junipers known for blue or gray foliage, can alternatively be bright yellow. Golden arborvitae, golden honeylocust and golden Monterey cypress really stand out nicely against darker green.
Colorful foliage tends to be most colorful as it develops freshly in spring, and tends to fade somewhat through summer. Gold junipers can actually fade to basic green by autumn. Shade inhibits most types of coloration, but can show off variegation better. There really is so much variety with colorful foliage that it is impossible to generalize.
Up at high elevations and out in deserts, where sunlight is most intense, plants can actually get more exposure than they need. The bluish or grayish glaucous foliage of the Colorado blue spruce from the Rocky Mountains, and the century plant from the Sonoran Desert, is actually designed to reflect a bit of sunlight so that the foliage does not scald.
Plants from foggy coastal areas, and understory plants that naturally live below the canopies of larger trees, do the opposite. They are deep green to absorb as much sunlight as possible. This is why Monterey pine and Monterey cypress are the same shade of dark green; and why most ferns are such dark green. Only tree ferns that stand above lower plants are naturally light green.
This can make it difficult to brighten a dark spot in the garden, since most lightly colored foliage wants an abundance of sunlight. White or lightly colored flowers would theoretically work nicely, but generally are neither permanent nor abundant where shaded. Golden foliage, like that of golden elderberries, golden arborvitaes and golden junipers, is greener in the shade.
Variegated foliage is different. Even if the green parts of the foliage are greener where well exposed than where shaded, the variegated parts are always variegated. Some plants are variegated with white. A few are variegated with yellow. Those that tolerate shade can brighten shaded spots nicely, or at least add a bit of contrast to dark green.
Even if the big pastel flowers of variegated angel’s trumpets and variegated hydrangeas do not stand out as well as they would against deeper green foliage, the foliage provides its own contrast. A concern with hydrangeas, as well as variegated dogwoods, is that they are deciduous, so lack foliage through winter.
Variegated Pittosporum tobira and variegated euonymus have smaller evergreen leaves. Variegated ivies are nice ground covers. On a smaller scale, so is dead nettle. Euonymus, pittosporums and ivies will sometimes need to have more vigorous unvariegated stems pruned out before they overwhelm and replace variegated growth.
The deeply colored foliage of black mondo grass, Ophiopogon planiscapus ‘Nigrescens’, is about as convincingly ‘black’ as foliage can get. It is darker than bronze New Zealand flax, purple leaf plum or bronze coral bells. Only purple beech or chocolate coleus are comparable. The foliage is dark enough to contrast very well against lightly colored planters or gray concrete, so works well in urns or mixed perennials, and bordering walkways. If it gets enough sunlight, black mondo grass makes a nice small scale ground cover under Japanese maples.
Mature plants stand only about half a foot tall, and spread slowly. The happiest plants can get nearly twice as tall. The softly cascading leaves are only about a quarter inch wide. Small spikes of tiny pink flowers that sometimes bloom in summer would contrast nicely against the dark foliage, but are rarely seen above the foliage. Black mondo grass prefers rather rich soil and somewhat regular watering. However, as they disperse roots, older plants do not seem to mind too much if they briefly get a bit dry.
It is easy to mistake various cultivars of Dyckia for diminutive relatives of Agave or Yucca. They form stout rosettes of rigid leaves with wickedly sharp terminal spines. Their comparably nasty but incurved marginal teeth resemble those of most species of Agave, but are generally more abundant. Surprisingly though, Dyckia are instead related to bromeliads. They just happen to be xeric.
Dyckia do not bloom much, but when they do, the tall and arching floral stalks really are more typical of bromeliads. As they bloom late in spring or in summer, the many small individual flowers on each stalk are collectively colorful enough to be delightfully popular with hummingbirds, butterflies and bees. Bloom is most commonly rich reddish orange, but some cultivars bloom red or yellow.
No one seems to mind that Dyckia does not often bloom. The foliage is remarkably striking alone. Many cultivars form dense mounding colonies of pups that, although unpleasant to handle, can be divided for propagation. A few toothless cultivars, armed only with terminal spines, are easier to handle. Individual rosettes can be as tall and broad as a foot. Dyckia do not need much water.
These are two pictures that did not make the grade for my ‘Six on Saturday‘ post this morning. That post featured bronze and gold foliage. Actually, of the six, only two were bronze, and only one was truly gold. One that I passed off as bronze was more purplish. Two that I thought were gold were just variegated with yellowish green and white.
I am none too keen on bronze or gold foliage anyway. The only exception that I can think of is the old fashioned bronzed ‘Schwedleri’ Norway maple. It was planted as a street trees on a few streets in the Santa Clara Valley in the 1950s.
Bronzed cultivars are less vigorous than their greener counterpart.
Gold cultivars are even less vigorous, and susceptible to scorch.
The best quality about bronze and gold is that they make silver look so good.
Olympic medal designations really should be reconsidered.
I only featured bronze and gold foliage earlier because I liked the contrasts between two different cultivars of each of the three species that were featured. Ironically, none of the three pairs compared bronze to gold directly. One compared purple to gold. The other two compared bronze to variegation that was barely yellow. Oh well.
There are neither bronze nor gold cultivars to compare to the silver foliage of the two species shown here.
I do not know what species of agave this is. There are not many distinguishable features visible in the picture above. The color and texture of the foliar surface might be identifiable to an expert. The little snail does not seem to be at all concerned.
The Eucalyptus cinerea in the picture below was pruned aggressively last autumn, both to contain the disfigured canopy, and also to stimulate more vigorous new juvenile growth. It is now strikingly silver.
In California, it is hard to imagine that hinoki cypress, Chamaecyparis obtusa, gets big enough to be harvested for lumber in Japan. Almost all of the local garden varieties stay quite short. The largest rarely get up to second story eaves. The most compact types that are grown for bonsai, do not get much more than a few inches tall. Most are somewhere in between, to about ten feet tall.
The ruffled sprays of evergreen foliage are surprisingly dense relative to the soft texture and often irregularly loose branch structure. Mature trees often shed branches to reveal sculptural reddish trunks and limbs within, while maintaining the distinct density of their foliar tufts. The minute leaf scales have rounded tips. (Other specie have pointed leaves.) Tiny round cones are rarely seen.
Because of slow growth and irregular form, hinoki cypress is an excellent specimen ‘trophy’ tree, but not so useful as hedging shrubbery. It prefers a bit of shade, and will tolerate considerable shade. However, varieties with yellow new growth are more colorful with good (but not harsh) exposure. It does not take much pruning and grooming to enhance form and expose branch structure.
The best and brightest color in the garden is obviously still provided by flowers. Autumn color can be spectacular, but only amongst relatively few deciduous trees, shrubs and vines that turn color reliably in mild climates, and only if the weather is conducive to coloration. The next best option for color beyond green is the sort of colored foliage that does not wait for autumn to materialize.
Foliage can be shaded with varying degrees of yellow, red, pink, purple, bronze, grayish blue or gray, or variegated with white, yellow or silvery gray. Plants that display such colorful foliage can be as small as flowering annuals, or as substantial as shade trees. Many are deciduous plants that also turn color in autumn. Most of the best are actually evergreen, so hold their color through winter.
Color tends to be richest as new foliage emerges in spring, and fades more or less through summer. Gold junipers only start out gold, but then fade to green within only a few months. The purplish foliage of ‘Forest Pansy’ redbud fades to coffee stained green. Yet, bronze New Zealand flax is always bronze. Dusty miller is always gray. Some plants are more reliably colorful than others are.
Exposure is important too. Most blue or gray foliage, whether juniper, agave, spruce, eucalyptus, olive or silver Mediterranean fan palm foliage, will be significantly greener if shaded. However, white variegation of English holly, hydrangea, ivy, hosta and pittosporum have better contrast if partly shaded. Colorful Japanese maples color better with good exposure, but roast if too exposed.
Many plants with colorful foliage are notorious for developing greener mutant growth known as ‘sports’. Because sports have more chlorophyll, they grow more vigorously than more colorful growth does, and can overwhelm and replace the more desirable colorful foliage if not pruned out. Many types of white or yellow variegated euonymus, as well as the more intricately variegated New Zealand flax, can revert to monochromatic green within only a few years.