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Shade Trees

Trees are the most substantial components of a landscape.

Shady characters inhabit some of the best gardens. Actually, most of the best gardens have some sort of shade tree. There are so many to choose from for every sort of garden. Some stay small and compact enough to provide only a minimal shadow for a small atrium. Others are large enough to shade large areas of lawn.

Like every other plant in the garden, shade trees should be selected according to their appropriateness to particular applications. Favorite trees are of course welcome, but should be placed in appropriate locations where they will be less likely to cause problems later. For example, those of us who like silver maples should only plant them where they will not crowd other trees, and if there is sufficient area to accommodate them when mature. Southern magnolias are bold shade trees, but create too much mess for infrequently raked lawns, and create too much shade for many other plants around them.

Shade trees near to the home should be deciduous if possible. This means that they will drop their leaves to be not so shady when it would be good to get more sunlight through winter. Honey locust, red oak, Raywood ash, tulip tree and many varieties of maple (except Japanese maple) are some of the best. Silver maple gets a bit too large for small gardens, but is an elegant shade tree for large lawns. Japanese maple and smoke tree are small trees that fit nicely into an atrium or a small enclosed garden.

Evergreen trees also make good shade trees, but should be kept farther from the home if possible, in order to avoid shading too much through winter. Besides, most evergreen trees are messier than deciduous trees so are not so desirable over lawns, patios or roofs. Camphor tree and several of the well behaved eucalypti are delightful shade trees where their litter will not bother anyone. Mayten tree is a smaller tree for more confined areas. Strategically placed evergreen shade trees can also function to obscure unwanted views.

Every shade tree creates a specific flavor of shade. Honey locust makes just enough shade for summer weather without making the garden too dark for other plants and lawn grass. Silver maple is a bit shadier. The shade of redwood and Southern magnolia (when mature) though, is so dark that not many other plants want to get close to them.

Remember that appropriate shade trees may be in the garden for decades or even centuries. It is best to select them accordingly so there will be fewer problems in the future.

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Douglas Fir

Douglas fir is rare within landscapes.

Within home gardens, Douglas fir, Pseudotsuga menziesii is very rare. So is the bigcone Douglas fir, Pseudotsuga macrocarpa of Southern California. However, they are not rare in the wild. Sometimes, suburban or rural home gardens develop around them. They can be awkward to accommodate. They are magnificent trees, but simply grow much too big.

Contrary to its rarity among home gardens, Douglas fir is actually common within homes. after all, most houses are constructed mostly of Douglas fir lumber. Most Christmas trees here are plantation grown Douglas fir. It is a major lumber plantation commodity in Chile, Argentina, New Zealand and Europe. Douglas fir is the Official State Tree of Oregon too.

Douglas fir is a grand tree in the wild. Old trees can grow more than two hundred feet tall with trunks eight feet wide! Their limbs may extend more than thirty feet from their trunks. It is obviously disproportionate for home gardens. Its soft evergreen foliage is delightfully aromatic, though. Its flattened, two-ranked needles are less than an inch and a half long. The female cones exhibit uniquely lacy scales.

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Spontaneous Limb Failure Among Trees

Willows commonly exhibit spontaneous limb failure.

Soil saturation is detrimental to trees for a few reasons. Excessive irrigation is almost as problematic, even without saturation. Chronic excessive moisture compromises stability by inhibiting deep root dispersion. Instead, it promotes shallower root buttressing. It may compromise structural integrity, too. It is generally the cause of spontaneous limb failure.

Spontaneous limb failure is exactly what it implies. Its spontaneity is what makes it more hazardous than limb failure caused by wind. It happens while the weather is calm, warm and perhaps humid, when least expected. Limbs might sag and produce cracking noises immediately prior to falling. However, they quite often fall suddenly and without warning.

Spontaneous limb failure is associated more with gravity than wind. It occurs as vigorous stems literally grow faster than they can support. Warm weather accelerates foliar growth that increases weight. A lack of wind and perhaps enhanced humidity inhibit evaporation from foliar surfaces. Inhibition of evapotranspiration limits weight loss during weight gain.

Deciduous trees are generally more susceptible to spontaneous limb failure. Sweetgum, willows, poplars and elms are particularly vulnerable. A few evergreen trees are likewise susceptible, though. They include coast live oak, Monterey cypress and a few eucalypti. Fruit trees exhibit spontaneous limb failure if they can not support the weight of their fruit.

The potential for spontaneous limb failure is rarely obvious. Limbs of some types of trees may visually appear to be too heavy or floppy. Limbs of Monterey pine, for example, may lean to one side if they sag prior to failure. However, valley oak, carob and sycamore are notorious for concealing their weaknesses. Even arborists can not predict all limb failure.

Wild trees within new landscapes are particularly vulnerable to spontaneous limb failure. They are not accustomed to irrigation through otherwise arid summers. Some can adapt as landscapes with irrigation develop around them. Others overindulge and become too heavy for their own trunks or limbs to support. New trees adapt to irrigation as they grow.

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Apricot

Some late apricots are still ripening.

Apricot trees, which are mostly of the species Prunus armeniaca, have history here. Vast apricot orchards formerly inhabited the Santa Clara Valley. Many remain as a significant industry of the San Joaquin Valley. Apricot trees are both famously reliable and famously productive here. If they can not inhabit orchards, they can be as happy in home gardens.

Home garden apricot trees are not quite the same as orchard trees. Most are grafted onto dwarfing rootstock to stay more compact than orchard trees. More cultivars are popular in home gardens than in orchards. Regardless, even relatively compact home garden trees need dormant pruning in winter. Otherwise, they provide more fruit than they can support.

Apricot trees change with the seasons. They are strikingly bare while dormant for winter. Their profuse white bloom is spectacular for early spring. Their rich green foliage mostly obscures their fruit as it ripens through early summer. It then turns cheery yellow before it defoliates in autumn. Home garden trees should be about ten feet tall with good pruning. Fruit is difficult to reach in overgrown trees.

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Catalpa

Catalpa bloom may be too high to see.

Those who know trees mostly agree that the more traditional catalpa, Catalpa speciosa, from the Midwest is the best catalpa, with soft leaves between half and a full foot long. In late spring or early summer, impressive upright trusses suspend an abundance of bright white, tubular flowers with yellow or tan stripes and spots at their centers. Individual flowers are as wide as two inches. Mature trees can be taller than forty feet and nearly as broad.

From the Southeast, Catalpa bignonioides, is a bit more proportionate to urban gardens though, since it only gets about seventy five percent as large, with leaves that are not much more than half as long. The flowers are also smaller, and not quite as bright white, but are more abundant than those of Catalpa speciosa are. The stripes and spots at their centers are slightly more colorful purplish brown and darker yellow.

Both catalpas can be messy as their flowers fall after bloom.  Fortunately, the big leaves are easy to rake when they fall in autumn. Long seed capsules that look like big beans linger on bare trees through winter.

Catalpa speciosa is almost never seen in modern landscapes, and not exactly common even in older Victorian landscapes around downtown San Jose. A few remarkable specimens remain as street trees in older neighborhoods of Oakland, Burlingame and Palo Alto. Most young trees were not planted, but instead grew from seed from older trees that are now gone.

Catalpa bignonioides is actually quite rare locally. A few old but healthy specimens can be seen around downtown Felton, with a few younger trees that grew from seed around the edges of town. Trees in Golden Gate Park in San Francisco are not as happy because of cool and breezy summers and mild winters.

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Tree of Hippocrates

Platanus, or sycamore, supposedly derives its botanical name from the Greek word “platys”, which means “broad”, and describes its wide leaves. However, some believe that its name was derived from “Plato”, who lectured about philosophy within the shade of a sycamore grove, rather than an olive orchard, outside of Athens. The Tree of Hippocrates, is an individual Platanus orientalis that was planted centuries ago, supposedly where Hippocrates lectured about medicine under a much older tree of the same species. Trees grown from cuttings and seed from the Tree of Hippocrates have been shared with medical institutions, schools and libraries all over the World. One seedling was planted at Dominican Hospital in Santa Cruz in 1968. Until only the last few years, it had been pollarded in an exemplary manner, which left no twigs for me to get cuttings from during winter. Only last summer, a gardener left me a few twigs, which I plugged as early cuttings. Of course, most succumbed to summer warmth. Some of the survivors did not root through winter. Now, though, there are four surviving rooted cuttings! So, we have four copies of a seedling of the second Tree of Hippocrates! Does that count for anything?

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Boinkification

Dwarf Alberta spruce needs to know its place.

Many dwarf plants are very practical. The many different dwarf cultivars (cultivated varieties) of false cypress that are grown for their interesting forms, textures and foliar colors are much more proportionate to home gardens than similar specie in the wild, which are big enough to get harvested for timber. Oranges are easier to reach on dwarf trees than on standard trees, which get as big as shade trees.

However, not all plants should be bred to be dwarfs. Dwarf Southern magnolias certainly have their appeal for tight spots, but do not make as much shade as larger trees do. Compact cultivars of crape myrtles (although not actually dwarfs) take too much time to grow above truck traffic to be practical as street trees.

Many classic annuals and perennials are likewise bred to be too compact to be as practical as they were in the past. Annie of Annie’s Annuals in Richmond refers to this all too common practice as ‘boinkification’. It makes many blooming plants more marketable and resilient to shipping and installation, but deprives them of their natural form and elegance.

Short annuals and perennials certainly have their place. Lobelia, sweet alyssum, dwarf marigolds and petunias are fine along walkways and in pots with other larger plants. They also work well as bedding plants for a profusion of color. Yet, there is all too often too much of a good thing. Some flower beds are simply so big and plain, that it would be just as colorful to paint an area orange instead of planting so many marigolds.

Taller flowering annuals like nicotiana (flowering tobacco), cosmos and zinnias add depth behind lower growing annuals. Dahlias are perennials that can accomplish the same thing. Some of the older and less common varieties of familiar bedding plants that have not been so boinkified also work well. There are even petunias that can get two feet tall and wide! These taller plants also provide cut flowers; which is something that boinky plants are not so good at.

Boinkification also compromises fragrance and aroma. Bedding dianthus have almost no fragrance at all; unlike the old fashioned dianthus and carnations that had such distinctive spicy fragrance. Modern zonal geraniums are more colorful than classic varieties, but their foliage is not quite as aromatic.

Not only does increased foliar density of boinky plants promote the proliferation of many diseases and pests; but the genetic violations necessary for boinkification interfere with resistance to diseases and pests!

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Silver Mountain Gum

Silver mountain gum needs no irrigation once established.

The bulky trunk and limbs, and shaggy bark of silver mountain gum, Eucalyptus pulverulenta, seem like they should be associated with a more imposing tree. Mature specimens are rarely more than twenty five feet tall. Those that try to get taller often fall over or break apart because they are unable to support their own weight, particularly if watered too generously. Aggressive pruning in spring and summer limits size, and also promotes an abundance of silvery juvenile foliage, which is popular as cut foliage.

Juvenile leaves are round and sessile (without petioles or stalks), and arranged in strict four-ranked formation. (Each pair of opposite leaves alternates with similar but perpendicular pairs.) Adult foliage is almost lanceolate (lance shaped) and not quite as silvery. Small, white, staminate flowers (without obvious petals) bloom between leaves from autumn through winter. Young stems have peeling bark.

Like almost all eucalypti, silver mountain gum gets established most efficiently and grows best if planted while small. They are actually best grown from seed, which can sometimes be obtained online. The next best option, which is actually least common, is #1 (1 gallon) trees. #5 (5 gallon) trees are typically the smallest trees available. Larger trees are likely to have problems dispersing their roots. Once established, silver mountain gum needs no fertilizer or watering.

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Deodar Cedar

Deodar cedar develops casual conical form.

“Cedar” is a common name of a few species of a few genera that are not actually cedars. Western red cedar is an arborvitae. Eastern red cedar is a juniper. Deodar cedar, Cedrus deodara, happens to be one of only three real cedars. Atlas cedar and cedar of Lebanon are the other two. Cultivars of Atlas cedar are uncommon. Cedar of Lebanon is very rare.

Although too big for compact gardens, deodar cedar is one of the more popular conifers. It performs splendidly within local climates and soils, as if it is right at home. Mature trees can survive without irrigation. Roots are generally complaisant, and disperse too deeply to displace pavement. However, deodar cedar can grow fifty feet tall and thirty feet wide.

Deodar cedar mostly develop casually conical form. Some develop multiple trunks or big limbs that eventually curve upward like trunks. Otherwise, limbs tend to droop somewhat at their tips. Glaucous grayish needle leaves are about an inch or two long. Most occur in terminal clusters of short spur stems. Some develop singly on elongated vigorous stems. Foliar debris has an herbicidal effect on the ground below.

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Street Trees Must Be Adaptable

Pavement necessitates trees with complaisant roots.

Trees of substantial size are not as popular as they had been among old home gardens. Modern landscapes of bigger homes on smaller parcels can not accommodate as many. Clearance from various infrastructure is now more of a concern than shade. Within many modern urban gardens, most available space is in front. Such is the realm of street trees.

This is not because of a lack of obstacles, such as infrastructure that requires clearance. It is more because such obstacles are closer to the ground with more open space above. Many street trees must actually be more adaptable to certain constraints than other trees. Selection of such trees, if allowable by their municipalities, necessitates diligent scrutiny.

Street trees are, most simply, trees between curbs and sidewalks. Some inhabit medians while others are adjacent to curbside sidewalks. Many municipalities prescribe particular trees for particular situations. Anyone who is uncertain of such limitations should inquire. Many municipalities permit property owners to install any trees they prefer, or none at all.

For those who can select street trees, such trees must be appropriate to their application. They must grow high enough to not obstruct sidewalks or roadways. Both sidewalks and roadways require minimal clearances. So do street signs, streetlamps and traffic signals. However, street trees should not grow too large for the confined spaces that they inhabit.

This includes their roots. Aggressive roots of willows, poplars and sweetgum are likely to displace pavement. Oaks, although too big for confined situations, are more docile. Their roots are less likely to displace adjacent infrastructures. Crape myrtle has become overly common because it is too small to cause damage. It does not make much shade, though.

Crape myrtle might also get rather messy, which is another consideration for street trees. It drops flowers during summer, and can get infested with scale, which exude honeydew. Magnolias drop flowers that can be a slipping hazard. Whether deciduous or evergreen, street trees should be reasonably tidy. Over roads, they should not need much attention.