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Reports from from Past Activities

Urban Trees Kevin Conrad

Choosing trees for the city and suburbs

"We garden in interesting times" said Kevin Conrad, speaking on February 20 to the Takoma Horticultural Club about choosing trees for urban settings. "Imagine you were a maple with fluctuating temperatures, 40 degrees one day, 60 the next, derechos, hurricanes . . ."

He then discussed and illustrated a number of attractive trees that are suitable for urban planting and streets and in gardens. A qualification is that they not grow to more than 30 feet in height, so they do not reach overhead wires and attract Pepco’s ungentle attention. On the other hand, "we force trees to do things that they don’t really want to. A catalpa that should be 75 - 100 feet is forced into a small umbrella shape." ‘Right plant, right spot‘ should be the guideline.

Examples of ‘right trees‘ for some urban spots included new or overlooked maples such as Acer buergerianum, which has exfoliating bark and good fall color, and will stay in the 25-foot range for 30 years. A. truncatum and A. campestre are other choices. Triflorum, related to the paperbark maple, can be seen in the Asian valley at the Arboretum, and A. miyabei “State Street“, from Morton Arboretum in Chicago, is a "Power Tree", recommended for planting under power lines.

Crape myrtle hybrid “Natchez“ is a work horse, beautiful in all seasons, particularly the purple leaf forms, said Kevin. (There are several other variable-sized crape myrtles that do not need pollarding to regulate growth.) For tulip poplar, choose a compact type with an open canopy such as Liriodendron “Ardis“ or “Little Volunteer“. The circumference of ‘Little Volunteer’ is 20-25feet, and you can garden under it. It has a smaller flower and a much smaller leaf than the species. Tennessee nurseries are ramping up production of this.

The dogwood ‘Venus’ is a hybrid between Cornus nuttallii and C. kousa with wide white bracts. It is disease- resistant and durable, with good fall color.

Variegated C. officinalis is hardy, has early bloom with a yellow flower, and is starting to bloom RIGHT NOW. It reaches 20 feet, with quarter-size fruit (from which you can make liqueur!!) and four season interest.

Kevin said that crabapples need no longer be messy, and there are many disease-resistant varieties such as Malus ‘Adirondack’ and ‘Red Jewel’. Chamaecyparis ‘Filifera Aurea’, with golden foliage, is a slow grower and can take 30 years to reach 30 feet. It displays one or more beautiful colors in fall. Native American Smokebush (Cotinus obovatus, found in Tennessee, Kentucky, North Carolina) is very hardy. It’s not for a courtyard setting, needs to be seen from a distance to be appreciated.

Pistacia chinensis is drought tolerant, with dark, corky bark and excellent fall color. A Japanese apricot ‘Peggy Clark’ is the equal of the Yoshino cherry, Kevin said, with a double, deep rose flower and a red calyx. Thuja ‘Green Giant’, a hybrid of Japanese and western thuja, can be substituted for Leyland cypress as a screening plant. Also check out the cherry Prunus campanulata ’First Lady’, which will be planted at the USDA complex in Beltsville, on the left side going north on Route 1.

It was pointed out that most of the trees on the list were sun-lovers. For shade, Kevin suggested that you look in a given genus for an understory species. For maples, an example would be the striped bark maple, A. pensylvanicum. Zelkova is overused, Kevin said. "There is a wealth of diversity" coming from nurseries today that can be reflected in our urban plantings.

Kevin Conrad is Curator of Woody Plants at the National Arboretum.

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