Extension Communications Extension 4-H Youth Building Ames, Iowa 50011-3630 (515) 294-9915

9/13/04

Contacts:
Mark Gleason, Plant Pathology, (515) 294-0579, mgleason@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Garden Column for the week of Sept. 17, 2004

More of My Favorite Trees

By Mark Gleason
Plant Pathologist
Iowa State University Extension

A couple of years ago, I used this column to sing the praises of ten especially tough and beautiful trees for Iowa. My list included white pine, Kentucky coffee tree, Norway spruce, crabapple, Japanese tree lilac, serviceberry, bald cypress, black walnut, catalpa and ginkgo.

I'd like to add a few more favorites to the list. My perspective comes from 20 years of diagnosing tree problems in Iowa, and admiring the trees that evade problems. The three trees I'll mention today are no less worthy than the first ten. I just didn't want to reveal all of my favorites at once.

First on the hit parade this time is arborvitae (Thuja occidentalis), also known as northern white cedar. It's not really a cedar, but never mind that. It's a beautiful evergreen with soft, vibrant green foliage that adapts well to a wide range of Iowa soils and sites.

One of arborvitae's outstanding virtues is its versatility in the landscape. Standard arborvitae can grow to 35 to 40 feet in height, but its cultivated varieties vary in shape and size from small and stubby to tall and columnar. Slow growers that respond well to pruning, arborvitae are among the most commonly used foundation plantings around buildings.

Arborvitae are nearly trouble-free. They almost never fall prey to diseases, and have few insect problems. Their main vulnerabilities are physical. They can suffer some browning of foliage in the winter, especially when planted in dry locations. Heavy, wet snow can bend down the branches, so it's helpful to shake off the snow as soon as you can.

Otherwise, arborvitae are wonderful plants. I think so highly of them that I planted two in my own yard.

My next favorite is honey locust (Gleditsia tricanthos). No, not the native honey locust with the frightening thorns. I'm talking about the thornless variety (G. triacanthos var. inermis) that is commonly planted in our landscapes. Thorns or not, this is a tough tree. It's also fast-growing, and can eventually reach 60 to 80 feet tall.

I've gained more respect for honey locusts as I've watched them cope with the challenges of surviving in tiny tree pits in Ames' Campustown area. Even when the rooting environment consisted mainly of cement chunks and pop cans, honey locusts found a way to succeed. They can make it in dry soil, compacted soil and even dysfunctional tree pit soil.

Another plus for honey locust is its open shade. Its small leaflets make for a pleasant, dappled shade that provides enough light for turfgrass to flourish. As a result, honey locust is more compatible with underlying grass than a heavy-shaded tree such as maple or oak.

Okay, honey locust has a few issues. Some varieties produce long, brown, extravagantly twisted pods that eventually drop to the ground and create a raking chore. But others never produce pods, including the varieties Green Glory and Halka.

Honey locust has acquired a bad reputation in some circles due to overplanting. Mimosa webworm, borers and fungal cankers can beset the tree, especially where dozens of them are planted, colonnade style, along streets. Like most trees, honey locusts are best suited to planting in ones or twos, not in masses. It's advisable to avoid the variety Sunburst, despite it attractive golden-leaves, since it's especially susceptible to fungal cankers. Another pointer: honey locust does best in full sun, so avoid shady sites.

No list of great Iowa landscape trees should leave out black maple (Acer saccharum var. nigrum). A so-called "hard maple" along with its close relative, sugar maple, black maple is a superlative shade tree for a large yard. It is native to Iowa's river valleys, but adapts well to fertile, well-drained urban sites.

For the past 18 years, I've admired the pair of mature black maples that occupy the parking area in front of my house. At a height of 50 feet, they create a pool of peaceful, forest-like shade in our neighborhood. These trees are stately and attractive all year, even in winter. But they are spectacular in the fall, when their leaves turn a vivid golden yellow.

I've seen very few diseased black maples, and their insect problems are minimal. If you're ambitious, you can even make maple syrup from their sap. If I could use only one word to describe black maple, it would be "classy."

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Editors: There are no photos available for this column.

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