Trees are nearly always selected for their flowers, foliage, or form.
Yet, at this time of year, there is an often overlooked arboreal feature that may achieve sudden prominence in the garden. In winter, when most flowering ceases and deciduous trees shed their leaves, the stuff that covers branches and tree trunks, otherwise known as bark, may take the biggest bite out of our botanical observations.
Crape myrtle is probably the most popular flowering tree in Los Angeles. There are at least 50 crape myrtle varieties available in the nursery trade. Unfortunately, the varieties with stunning bark, the so-called cinnamon siblings, are seldom seen. I often wonder what our parkways would look like in winter if the crape myrtles planted there possessed colorful bark. It appears that these cinnamon cultivars are more expensive than their more common kin.
Monrovia Nursery, which supplies crape myrtles to local retail nurseries and others, carries several cinnamon bark varieties, including the heavy blooming, white-flowered `Natchez,’ lavender-pink `Muskogee,’ and true pink `Pecos,’ an excellent selection for small spaces that grows to only 8 feet tall and 6 feet wide. These varieties are all mildew-resistant `Fauriei’ hybrids with leaves that turn brilliant orange or red in the fall.
The Catalina ironwood (Lyonothamnus floribundus), whose name describes the color of its bark, is a California native evergreen with a columnar growth habit and highly unusual fern-like foliage. Incense cedar (Calocedrus decurrens) is distinctive and never requires pruning as it develops a perfectly symmetrical pyramidal shape with reddish bronze bark.
The deciduous red or river birch (Betula occidentalis) has smooth coppery bark highlighted with white lenticels or slits which facilitate gas exchange between the trunk’s interior cells and the outside air. Red birch grows slowly to around 40 feet and, although a California native, requires regular moisture because of its riparian habitat, which means that it grows naturally on the banks of rivers or streams. And, of course, there are plenty of European white birch (Betula papyrifera) planted in Southern California, although their lifespan in our dry environment, which is antithetical to their habitat, is usually around 15-20 years.
The last cinnamon bark tree that must be mentioned is big berry manzanita (Arctostphylos glauca). It grows slowly to a height of 20 feet with an equal spread. Two trees with green trunks deserve mention. One is palo verde (Parkinsonian spp.), which means “green stick” in Spanish and references its green photosynthesizing bark. The other is the thorny kapok or floss silk tree (Chorisia/Ceiba speciosa) with spongy green bark. It is the last tree to bloom in the fall with large silky, five-petaled flowers in deep pink with yellow centers. This species may grow up to 60 feet tall but Pink Princess is a dwarf variety that reaches only 12 feet in height.
I cannot say enough words of praise for our deciduous, California native white alder (Alnus rhombifolia). Its whitish to ash gray bark is marked with captivating eye-shaped scars, indications of where branches were once attached. When given ample space, this tree is highly symmetrical and requires little pruning even after it reaches its mature height of 50 feet. Its shimmering green foliage always looks like it has just been washed in the rain. California sycamore (Platanus racemosa) is another deciduous native. Its exfoliating bark reveals a mottled trunk whose sight may leave you lost in contemplation of its artistic design. Both of these trees, although drought tolerant, are riparian and are not bothered by regular irrigation. White alder, in fact, will look much better when soil is kept slightly moist.
No discussion of beautiful-barked trees would be complete without mention of the lemon-scented gum (Eucalyptus citriodora). The alabaster bark of this beauty gives it a unique presence. A Mindanao gum or rainbow eucalyptus (Eucalyptus deglupta) grows famously on the edge of the UCLA Botanical Garden in Westwood, with peeling bark that is painted in pink, lavender and yellow-green. This tree is tropical and cold-sensitive so that it should be given ample summer water and frost protection until it is robust enough, after a few years in the ground, to fend for itself.
Last but not least, the cork oak (Quercus suber) is noteworthy due to its spongy, hydrophobic bark. To appreciate this evergreen tree, observe a row of them growing along the west side of the Van Nuys courthouse. The corks you popped on New Year’s Eve came from this tree, which is grown primarily in Portugal and Spain, but also in France, Italy, Morocco, Algeria and Tunisia. Harvesting the cork, or outer bark of these trees, is a special skill done entirely by hand. Improper harvesting procedures can kill a tree.
Normally, a cork oak is allowed to grow for 25 years before the virgin layer of cork is harvested. When harvesting is done correctly, the tree is not damaged and will regenerate another layer of cork in about 10 years. There are approximately 10 cork harvests during a tree’s productive life of 150 years, while a tree’s life span stretches to 250 years.
Cork oak forests are in danger of disappearing, but not due to overharvesting or mismanagement. The problem is that corks made of plastic and silicone are less expensive than real cork and these stoppers are gaining wider acceptance, resulting in less demand for cork and subsequent neglect of cork oak forests. Still, the lion’s share of premium wines continue to be stoppered with cork.
Cork oak itself is a fine drought-tolerant shade tree and may be grown in all of California’s deserts. It may be planted from the Antelope Valley to Palm Springs, the only caveat being that foliage may yellow in highly alkaline soil. To mitigate alkalinity, apply gypsum to the soil around the tree on a regular basis, at least once a year.
California native of the week: American or wild licorice (Glycyrrhiza lepidota) is indigenous to North America and may be found growing from California to Virginia. Its flavor is on par with that of the commercial licorice plant mentioned above that is native to the Mediterranean and West Asia. Our native licorice has attractive white flower spikes that bloom in the spring and will remind you of those you see on lupines, indicating their shared kinship as members of the legume family of plants. Wild licorice is a riparian species, meaning that it needs to be grown near a river or stream or where soil moisture is constant, and they will even accept clay soil. Like most other California natives, however, wild licorice prefers well-drained soil on the sandy side. Due to its rhizomes, it forms attractive clumps and its flowers are magnets to bumblebees and butterflies. If anyone knows of a source for wild licorice seeds or plants, please advise.
Are there any trees with memorable bark that you would like more people to know about? If so, tell me about them at joshua@perfectplants.com. Your questions, comments, gardening challenges, conundrums, and successes are always welcome.