Boulders In Modern Landscape Design

90703thumbIt is hard to say why boulders and sculptural stone are sometimes incorporated into American landscapes. A long time ago, boulders were only left in landscapes if they were to big and heavy to move out of the way or break apart. Early American landscapes were designed to express dominance over nature by replacing as much of it as possible with unnaturally organized landscapes.

Slowly through history, less refined and more relaxed landscapes became more tolerable, and then became popular as an expression of rebellion to earlier formality. Nowadays, most landscapes are inevitably informal, partly because so many believe that informality is more natural, and partly because few landscape designers will design anything else. Simplicity and symmetry are passe.

This informality allowed for the incorporation of various elements from various styles of landscaping, regardless of how incompatible some of such elements were with each other. Boulders and sculptural stone that had been traditional with many Asian styles of landscape design were added to American landscapes in rather nontraditional fashion. It has been a slow process of evolution.

Boulders are obviously nothing like viable and dynamic plant material, although they do contribute form, texture and color to a landscape. Designers might say that bigger and sculptural boulders add drama without even trying. In some situations, boulders are as functional as they are aesthetically appealing. They can obstruct unwanted traffic or hold back soil that is at a higher elevation.

If they need not conform to any of the various Asian landscape design traditions, there are not many rules for the use of boulders and sculptural stone. Exotic stone that might be incompatible to big open landscapes where exposed endemic stone is visible nearby, might be just fine in enclosed gardens where there is no reference for what is natural.

The standard rule of burying as much as two thirds of a boulder to make it seem as a natural outcropping is only valid if it is intended to look like a natural outcropping.

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Rain On The Shade Parade

60622thumbModern urban lifestyles are becoming less conducive to gardening all the time. Bigger and taller homes cast larger shadows over smaller garden spaces. The taller fences between these homes do not help. The densely evergreen trees employed to obscure the views of other larger and taller homes also obscure sunlight. Not much sunlight reaches the ground where shorter plants need it.

While all this is going on, we are supposed to be gardening with more sustainable plants that demand less water. Smaller, shadier and more sheltered gardens should naturally use less water than larger and more exposed gardens need. Yet, the plants that do not mind the shade naturally want more water than plants that want more sunlight. There are not many that are drought tolerant.

Drought tolerant plants are naturally endemic to dry climates. Many are from chaparral regions. Some are from deserts. In such ecosystems where water is too scarce to sustain much foliage, there is not much competition for sunlight. Shade tolerant plants are just the opposite. They are from forested ecosystems with taller and shadier trees. Such ecosystems are sustained by rainfall.

There are quite a few plants that do not mind a bit of shade. Heavenly bamboo, flowering maple, hydrangea, camellia, azalea, rhododendron, holly, daphne and andromeda (Pieris spp.) are some of the more familiar shade tolerant shrubbery; but alas, none are drought tolerant. Nor are the various ferns. Even small shade tolerant trees like dogwood want to be watered regularly.

Most of the plants that tolerate shade but are not too terribly thirsty are groundcover plants or perennials. They are not exactly drought tolerant, but can survive with minimal watering because they do not dry out so much in the shade. Once established in a cool shady environment, plumbago, lily turf, periwinkle Saint John’s wort and coral bells (Heuchera spp.) only need to be watered occasionally through summery weather, although they are thirstier in sunny spots. Both English and Algerian ivy need nothing in the shade.

Summer Turns Up The Heat

90626thumbDoes the heat seem to have come on suddenly this year? There was all that rain through winter, then a quick but delightful spring, and now it is suddenly over a hundred degrees in some places! What happened?! There is certainly nothing abnormal about such warmth in the middle of June. It just comes as a surprise when it arrives so suddenly after such pleasantly mild spring weather.

At least warm weather here is not as dreadful as it is in other climates. It cools down a bit overnight. Humidity is typically (although not always) low. There is typically at least a bit of breeze by late afternoon, just after the worst of the warmth. We need not contend with the sort of dankly humid heat, that lasts all day and into the night without even a slight breeze, that so much of America gets.

Of course, that is no consolation now. By our standards, it is hot. Gardening is no fun, and some of it gets neglected. We become more aware of where shade trees should have been planted. We might also notice wilted or pallid plants that are not getting enough water. Pruning that was delayed while new spring growth matured may need to be delayed a bit longer, until the weather cools.

Unfortunately, the minimal humidity and occasional breezes that make the weather more comfortable for us make it more uncomfortable for the plants in the garden. Plants can realistically tolerate more heat than we can, but prefer it to be in conjunction with humidity. Otherwise, they can lose too much moisture to evapotransipiration (evaporation from foliar surfaces), and wilt or desiccate.

Automated irrigation obviously needs to be adjusted accordingly. Potted plants need more of an increase than those in the ground. Those that are overgrown, in hanging pots, or exposed to the typical evening breezes will be the most consumptive. It is not always easy to know how much they need, but one can be certain that if they are wilting, they need more than they have been getting.

Pots exposed to sunlight can get uncomfortably warm. If cascading or bushy growth does not shade the south sides, smaller potted plants can.

Foliar Color Long Before Autumn

51104The 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.

Vines For Better Or Worse

90619thumbVines in the wild are downright exploitative. They do not support their own weight, so instead climb or sprawl over shrubbery and trees. Some are satisfied staying down below the canopy of the hosts who support them, as if aware that a healthy host will support them for a good long time. Many vines climb aggressively to the top and overwhelm their hosts, even if it eventually kills them.

There is nothing civil about the technique of the strangler figs, which incidentally includes two popular houseplants, fiddle-leaf fig (Ficus lyrata) and creeping fig (Ficus pumila). They wrap their hosts in networks of stems and roots that strangle the hosts as both the hosts and the clinging vines grow and expand. As the hosts die and rot, the vines develops into self supporting tree trunks.

That is how fiddle-leaf fig, as it is known as a houseplant, grows as a free standing tree rather than as a creeping vine. It is grown from cuttings from the self supporting adult growth rather than the creeping juvenile growth. Conversely, creeping fig is grown from juvenile vines, which find a support to cling to, and ultimately develop shrubby adult growth when they get to the top of the support.

English and Algerian ivies are not quite as aggressive, since they do not intend to kill their hosts. They are not often intentionally grown as vines, and are almost never planted anymore, but their juvenile growth still works as ground cover in many mature landscapes. One of the main problems with ivy is that it is constantly trying to climb walls and trees so that it can bloom and toss seed.

That is not such a problem on concrete walls, but ruins wooden and painted surfaces, and makes a mess of trees. Boston ivy (which is not really an ivy) lacks a juvenile ‘ground cover’ phase, but if kept off of painted and wooden surfaces, happens to work better on concrete infrastructures. It is important to know how a particular vine will behave before selecting it for a particular application.

Carolina jessamine, mandevilla, lilac vine and star jasmine are a few complaisant vines.

The Wrong Time For Pruning

80801thumbNot many plants are sensitive to mere heat alone. Actually, many plants prefer warm weather. The difficulty that some plants have with heat locally is that it typically accompanies aridity, and often accompanies afternoon breezes. As appealing as breezes and minimal humidity are to us while the weather is warm, they promote and accelerate desiccation of exposed sensitive foliage.

Pruning, which obviously becomes necessary while warm weather promotes growth, can make plants more sensitive to damage caused by warm, sunny, arid and perhaps breezy weather. It exposes formerly sheltered stems and inner foliage, which are more sensitive than outer foliage is, to more sunlight and drying breezes. Exposed foliage can either desiccate or roast, or both!

A bit of unsightly but relatively minor foliar damage on the extremities of the outer canopy might be only superficial, but major damage can be dangerous. Superficial damage often gets replaced by fresh new growth before it deteriorates enough to expose more foliage and stems below. However, recovery from major damage can be delayed by the distress associated with the damage.

Japanese maple, aralia, philodendron, rhododendron and all sorts of ferns can easily get damaged by increased exposure. Low ferns are not likely to become too exposed by any loss of their own foliage, but often become more exposed by the pruning of plants above them. Like frost damage, foliar scorch might need to be left to shelter remaining foliage until new growth develops.

The bark of many plants, although not susceptible to desiccation, is very sensitive to sun-scald if too exposed. Young and smooth bark is the most sensitive, particularly if it had always been shaded. Scald kills bark and the vascular tissue below. As it decays, it exposes interior wood to more decay that is likely to compromise the structural integrity of the affected stems and trunks.

Pruning during relatively cool weather and while there are a few relatively cool days in the forecast allows foliage a bit of time to adapt to a new exposure before the weather gets dangerous. Through summer, pruning should not be so aggressive that too much sensitive foliage or bark are exposed, even if it is necessary to leave a bit of unwanted sloppy growth to partly shade bark. Aggressive pruning of exposed and sensitive plants should be delayed until autumn, when sunlight is not so intense, and weather is cooler and wetter.

Deadheading Promotes And Prolongs Bloom

90612thumbApril showers bring May flowers. May flowers make a mess. Well, some of them do. Most simply disintegrate and fall from the trees, shrubs and vines that produced them, and decompose into the soil below. Some might have needed to be swept off of pavement and decks. Regardless, most of us do not notice the very minor consequences for the majority of spectacular spring bloom.

However, there are some flowers that demand a bit more attention after they finish blooming. They linger after the show is over, and can look shabby as they deteriorate. Small ones can simply be plucked. Larger blooms might need to be pruned out. The process of removing deteriorating blooms is known as ‘deadheading’, and it is done for more reasons than just to keep plants groomed.

Plants bloom to produce seed, and the production of seed takes resources. Removal of seed structures not only diverts resources to more useful functions, but for many plants, it also stimulates subsequent bloom in response to interrupted seed production. They literally keep trying until they are able to produce viable seed, even if they must continue all season until late autumn dormancy.

Most plants that benefit from deadheading are perennials. Shasta daisy, black-eyed Susan, blanket flower, cone flower, yarrow, lavender and beard tongue (penstemon) bloom more abundantly and for a longer time with regular deadheading. The various lavenders, as well as other perennials that are comparably shrubby, are easily deadheaded by shearing after profuse bloom phases.

For bulbs and bulb like perennials that bloom only once annually, deadheading will not promote subsequent bloom during the same year, but conserves resources for the following year. Daffodil, lily, clivia, various iris and, during summer, gladiolus and dahlia, all appreciate diligent deadheading.

Petunia and marigold are two annuals that happen to bloom better with regularly deadheading. They bloom so profusely that deadheading can be quite a chore. Plants that can be invasive, such as salsify, should be deadheaded before dispersing seed.

Ferns Are Shady But Cool

P90309+++++It could be either an asset or a liability. With few exceptions, ferns do not want to be too exposed to direct sunlight or wind, especially during warm and dry weather. However, as long as they get just enough filtered light, they can be quite happy in sheltered spots that are a bit too shady for other plants. Most like to be watered regularly, and perhaps lightly fertilized in spring and summer.

They provide neither floral color nor fragrance. They lack interesting branch structure and bark. Since they reproduce by spores, they do not even produce any fruit, either edible or ornamental. For those who do not know them any better, they might seem to be rather boring. Yet, those of us who grow them know how handsome their lush, finely textured and uniquely patterned foliage is.

Of the popularly grown ferns, only two develop ‘trunks’, (which are actually just clustered wiry roots growing downward through rotting stems). Two others are ‘epiphytes’ that naturally cling to trees or exposed stone, but in home gardens, are more popularly grown on wooden plaques. Most other ferns are terrestrial understory perennials that naturally live in the partial shade of larger plants.

Although mostly confined to the ground, some ferns can get quite large. Individual leaves, which are known as ‘fronds’, can get several feet long. Even before it develops a trunk, Australian tree fern produces huge fronds that can shade an atrium. Other ferns with smaller leaves can spread very efficiently, and can even become invasive. Fortunately, most ferns are relatively complaisant.

The two popular epiphytic stag-horn ferns have weirdly lobed but otherwise undivided fronds. Leaves of the odd bird’s-nest fern is neither divided nor lobed. Otherwise, fern fronds are intricately divided into small leaflets known as ‘pinnae’. These pinnae are neatly arranged on opposite sides of leafstalks known as ‘rachi’. Some ferns have silvery variegation, but most are rich dark green.

Ferns innately do well in pots. Boston, maidenhair, rabbit’s foot, holly and bird’s-nest ferns are actually excellent houseplants. However, Australian tree fern and a few others shed irritating fuzz that would be a problem in the home. Most of the popular ferns are evergreen. Many consume their own deteriorating foliage by covering it with new foliage. Some ferns need occasional grooming.

Spontaneous Limb Failure Is Real

90605thumbIt sounds like science fiction, but it is not. Every spring and during particular summer weather, limbs can fall from trees without warning, and seemingly for no reason at all. It happens when least expected, while the weather is warm and perhaps humid, but notably without wind. The lack of wind is what makes it so unexpected. It is a phenomenon known simply as spontaneous limb failure.

Those who witness it might think that the arborists they call to clean up the mess will not believe their descriptions of what happened. Yet, arborists are familiar with it. Quite a few species of trees are notorious for it, especially in urban landscapes where they get watered regularly. Most of such trees are either chaparral trees that do not expect much water, or riparian trees that do expect it.

Spontaneous limb failure occurs as warmth accelerates vascular activity, but humidity inhibits evapotranspiration, which is evaporation from the foliage. Accelerated vascular activity increases the weight of the foliage. Inhibition of evapotranspiration limits the ability of the foliage to eliminate some of the excess weight. Limbs break if unable to support the increasing weight of the foliage.

Spontaneous limb failure is not as easy to predict as the more familiar sort of limb failure that is caused by wind. Limbs that get blown down typically exhibit some sort of structural deficiency or disfigurement prior to failure. Some limbs that succumb to spontaneous limb failure do so as well, but most do not. They just happen to be the healthiest and most densely foliated parts of a tree.

Native coast live oak and valley oak are the two most familiar of the chaparral trees that are notorious for spontaneous limb failure. Native cottonwood, willow, box elder and sycamore are riparian trees that are perhaps even more susceptible to spontaneous limb failure. Sweetgum, carob, stone pine and various eucalypti are some of the exotic trees that might drop limbs spontaneously.

In summer, spontaneous limb failure is less likely as growth slows and limbs strengthen.

Try Some Unconventional Cut Flowers

P81214There is nothing like growing our own; whether vegetables, fruit or cut flowers. Most fruit and vegetables are grown to be eaten, so are not missed too much when harvested. Even colorful citrus fruit is better harvested than left out in the garden. No one wants to waste it. Flowers are not so simple. They are so colorful and fragrant in the garden, that it is tempting to leave them all out there.

Cosmos and many kinds of daisies are so abundant that there are plenty for both the home and garden. Gladiolus are not so fortunate. They bloom only once. Cutting the flowers to bring into the home deprives the garden of their color. What is worse is that cut gladiolus, although excellent cut flowers, do not last quite as long as they would in the garden. Roses at least continue to bloom.

Daylily can be a good cut flower, but individual flowers last only a day (obviously). This is not a problem in the garden because new flowers bloom daily to replace those that that have finished. Cutting stems not only takes flowers in bloom, but also takes the flower buds behind them that are waiting for their turn to bloom. However, not many, if any, of the unbloomed buds bloom once cut.

Many types of iris, except for Dutch iris, have the same problem. Attentive garden enthusiasts might leave iris to bloom in the garden, and might even groom fading blooms from fresh blooms on the same stems, and then cut stems to bring into the home when the last bud on each stem is just beginning to bloom. The last flowers are not as excellent as the first, but it is a fair compromise.

Cannas are not so functional. They are great in the garden for both flowers and foliage, but fade too soon in the home. Bougainvillea and crape myrtle stems likewise start to wilt and drop flowers immediately after getting cut, but for those who do not mind cleaning up after them, there are plenty of papery flowers to last a few days. The wilted tips of bougainvillea stems can be pruned out.

There are no rules to cut flowers. Lily-of-the-nile might seem like a silly choice, but works quite nicely for those who dare to try it. New Zealand flax flowers are not very colorful, but provide striking form. Zonal geranium and nasturtium work well with or without foliage attached. Lemon bottlebrush, photinia, New Zealand tea tree, bugle lily, various hebes, and all sorts of salvias are worth a try.