Underutilized Trees for Urban Use: American Smoketree

A young specimen and adjacent mature one can be found on the Hofstra University campus on Long Island. Photo by Michelle Sutton
A young single-stem specimen and adjacent mature multi-stem one can be found on the Hofstra University campus on Long Island. Photo by Michelle Sutton

During her 2014 New York ReLeaf Conference plenary talk, Urban Horticulture Institute Director Nina Bassuk lifted up some underutilized trees for urban use. One of them, American smoketree (Cotinus obovatus) was growing just outside the conference room doors on the Hofstra University campus, where a mature specimen stood protectively behind a newly planted youngster. American smoketree is native to the U.S. South and Midwest.

Naturally and by training, American smoketree has a more tree-like habit than European smoketree (C. coggygria), and it matures up to 30 feet (9 m) tall and 20-30 feet (6 to 9 m) wide—twice as big as C. coggygria. It is hardy to zone 4 or 5, depending on which reference you consult. It is deer resistant and tolerant of drought and poor soils but doesn’t like to have wet feet for prolonged periods. Missouri Botanical Garden voted it one of its “Tried and Trouble-Free” tree species.

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Underutilized Trees for Urban Use: Maclura ‘White Shield’

As part of her plenary talk at the 2014 ReLeaf Conference at Hofstra, Urban Horticulture Institute Director Nina Bassuk held up some underutilized trees that have worked well for her in Ithaca’s urban environs. Among them was ‘White Shield’ Osage orange (Maclura pomifera). In future posts we’ll cover others she recommended, like American smoketree (Cotinus obovatus).

'White Shield' foliage by Nina Bassuk
‘White Shield’ foliage by Nina Bassuk

‘White Shield’ Osage Orange 
‘White Shield’ is the most readily available cultivar of Osage orange (Maclura pomifera) on the market. Although Osage orange is native to Oklahoma, Arkansas, and Texas, it grows readily beyond its native range. Because of the thorny nature of its juvenile (non-fruiting) stems, it was used as a natural fence for keeping in livestock. By hedging the tree, the juvenile, thorny form is perpetuated. In Ithaca, there is a remnant of such a hedge right in the middle of a residential neighborhood.

Maclura fruit
Osage orange fruit is gorgeous, but impractical for urban use. Fortunately, ‘White Shield’ is fruitless. Photo Courtesy Cornell Woody Plants Database

Osage orange is dioecious, meaning that male and female flowers form on separate trees. This is important because the fruits on female trees are enormous, about 6 inches (15 cm) in diameter. They are a conglomerate of beautiful green seeds and fruit that hangs on the tree until ripe in early fall. They then fall to the ground and could cause injuries and property damage, not to mention the mess. I’ve heard it reported that the fruits repel cockroaches and were sold in urban greenmarkets as a natural insecticide.

Luckily, male (fruitless) cultivars like ‘White Shield’ are readily available. ‘White Shield’ is an exceptionally fast-growing form once established. Branches are distinctly upright with glossy green leaves. Another especially beautiful cultivar is ‘Wichita’, selected by the late John Pair. Both of these selections originate from Oklahoma.

The habit of a young ‘White Shield’ Osage orange in Ithaca by Nina Bassuk
The habit of a young ‘White Shield’ Osage orange in Ithaca by Nina Bassuk

Osage orange has a lot going for it as a tough urban tree. Once established, it tolerates very droughty, windy, and hot sites. It can handle a wide range of pH, including highly alkaline soils, and is purported to be tolerant of wet conditions as well. It can also tolerate salt spray. It has no serious pests, and transplants easily. It matures at 20 to 40 feet (6 to 12 m) tall and similar spread.

It is considered hardy to Zone 4a; however, we have occasionally noticed some twig dieback perhaps due to failure to harden off sufficiently before winter in our zone 5. It readily grows out of the dieback during the following summer. Fruitless cultivars of Maclura pomifera like ‘White Shield’ are definitely worth a look. —Nina Bassuk, Director of the Cornell Urban Horticulture Institute