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Photograph by Shari Kaplan
Midas Touch: Although named for its yellow flowers, the goldenrain tree is also known for its fruit capsules that resemble miniature paper lanterns.
Choosing a good street tree requires some care
By Tony Tomeo
Before I begin discussing another new topic, I feel obligated to conclude the discussion of street trees from two weeks ago. Most of my favorite street trees I wanted to list earlier exhibit most of the qualities I described as essential to such trees. Of course, no tree is perfect. Most will eventually cause some problems.
For example, the Norway maples so commonly planted at tract homes in the mid 1950s have a reputation of breaking sidewalks with their voracious roots. Oner should realize, however, that these trees are nearly half a century old. They were good street trees much longer than is possible for the London plane trees and Chinese pistaches that are now commonly recommended. Both these species could be causing similar problems in half that time.
Red oak, Quercus rubra, is one of my all-time favorite street trees. Although I do not know of a complete street collection, several can be seen at El Camino Hospital in Mountain View as well as a few on El Camino Real, also in Mountain View. Unfortunately, the red oak is the only oak I like as a street tree. Other oaks are either too messy or not suited to the environment. Holly oak is actually one of my least favorite trees because it is always infested with scale or aphids and is dripping with honeydew.
One of my other favorites is the red maple, Acer rubrum, and its cultivars. Contemporary hybrids and cultivars of Norway maple are also very useful. Although some of the older cultivars of Norway maple do produce voracious roots, most of these are not commonly available in nurseries. Red maples are green during the summer and should not be confused with some of the cultivars of Japanese maples that exhibit red foliage in the summer but are not suitable street trees.
The goldenrain tree, Koelreuteria paniculata, drops messy seed pods in winter, but is otherwise very well-behaved and agreeable to concrete pavement. I actually planted one in my own garden and two next door. Flowering pear, Pyrus calleriana, and its cultivars is also well-behaved and produces autumn color comparable to that of the maples and red oak.
My colleague Brent Green once wanted evergreen trees for his block of Sierra Bonita Avenue and selected the carrotwood tree, Cupaniopsis anacardioides, to replace messy old carob trees. It has been very satisfactory and much cleaner than most evergreens.
Many species of palm trees are useful as street trees, but removal of old fronds may be expensive as they grow beyond reach. Palms are also not appropriate to every style of landscape or neighborhood.
Communication with neighbors is helpful when selecting street trees. If uniformity on the street is preferred, residents may select a species suitable to all landscapes affected. Some neighborhoods may prefer to select more than one option.
Of course, there are far too many suitable street trees for me to list, but these are a few of my favorites. Other species that are less than ideal may also be considered if one is willing to contend with the associated problems. In fact, Brent and I once planted a station wagon full of manna gum eucalyptus in the median of a Los Angeles boulevard because it was what suited the surrounding neighborhood.
Tree of the Week: Goldenrain tree
Many garden enthusiasts find the distended papery fruit to be more intriguing than the loose clusters of very small yellow flowers that appeared earlier in summer. The capsules are very fragile when dry, but are often used in floral design. They hang on trees after defoliation in autumn and can be a slight mess as they deteriorate through winter.
Although the goldenrain tree, Koelreuteria paniculata, is more broad than tall at maturity, it prefers to spread its canopy above the height of truck traffic. The structure, in conjunction with the well-behaved root system, justifies its recent popularity as a street tree. Trees grow at a moderate rate to 20 to 30 feet tall and can eventually grow to 40 feet wide, but are easily contained.
The open canopy provides good shade that is not too dark for other species in the landscape below it. Foot-long leaves are composed of about a dozen two- or three-inch long lobed leaflets. Goldenrain trees tolerate adverse conditions and dense soil, but prefer irrigation when young. Because they are increasing in popularity, they may be obtained at many nurseries and garden centers.
Horticulturist Tony Tomeo can be contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.
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Campbell, California
