Once a popular street tree, the American elm has been largely wiped off the map by Dutch elm disease.
The American elm (Ulmus americana), with its large size and outstanding arching umbrella habit, was long considered the ideal street tree. Hardy and tolerant of urban conditions, it was planted by millions across North America and the “tree-lined street” many of us have in our imagination are of those endless rows of American elms. Unfortunately, its role as America’s favorite street tree came to a crashing halt with the arrival of Dutch elm disease (Ophiostoma spp.), a fungal disease carried from tree to tree by elm bark beetles. Once established in a tree, the fungus can then spread to neighboring trees through their roots when they touch.
Dutch elm disease probably originated in Asia, but went largely unnoticed there, as Asiatic elm species have good developed genetic resistance to it over thousands of years. It was first noticed in Europe in 1910, but was only identified in 1921 in the Netherlands (hence the name Dutch elm disease). It first arrived in North America in 1928 when elm wood from the Netherlands containing bark beetles was shipped to New York, then transported to Ohio, starting two separate outbreaks. Since then, it has spread widely and newer, more virulent strains of DED (Dutch elm disease) have only increased the problem.
The disease now occurs throughout Europe and much of the United States and Canada, although its spread westward has been partly checked by the Rocky Mountains. It’s presently absent from Alberta and British Columbia while elms in Quebec City and Winnipeg are “holding their own”, helped by their colder climates (the beetles that carry the disease don’t overwinter in the north, but can fly there from the South during the summer). More than 77 million elms have died of DED in North America so far. Today, in many areas, any mature elms that are left only survive because their owners are willing to pay for expensive preventative treatments that have to be repeated every 2 or 3 years.
Hybridization and Selection
Fortunately many researchers have been working on solutions since the 1940s and have come up with some interesting solutions.
Street planting of a naturally disease-resistant American elm, ‘Princeton’. Photo: Mr. Matté, Wikimedia Commons
For example, healthy, mature American elms have been found in areas otherwise devastated by the disease. Cuttings from these survivors have been tested and many were found to be resistant to DED, even when inoculated with the spores of the disease. They aren’t entirely immune to the DED: they may catch it if they are raised under stressful growing conditions, such as repeated droughts. Even so, some of these varieties that have been successfully used in landscapes for over 40 years and are still thriving.
Another possibility is using naturally disease-resistant Asiatic species as substitutes, notably the Japanese elm (U. davidiana japonica), which is remarkably similar in appearance to the American elm, although of a smaller size.
Finally, there is considerable hybridizing going on, notably between desirable North American and European species and disease-resistant Asiatic ones, and several very interesting hybrid elms, all with good DED resistance, are available in many nurseries.
Pick Own-root Elms
If you intend to buy a DED-resistant American elm (U. americana), make sure to get one growing on its own roots. To save production time, some growers have been grafting resistant varieties onto elms grown from seed, but this can allow the disease to enter the tree through its roots. It’s therefore best to choose trees identified as non-grafted or growing on their own roots.
Elms Resistant to Dutch Elm Disease
Accolade™ Morton’ elm is a hybrid that is now widely available on the market. Photo: Chicagoland Grows
What follows is a list of varieties of elm that offer both the majesty of the American elm and a good resistance to Dutch elm disease. Most nurseries will carry at least one of these varieties, so pick your favorite and help bring back the majestic American elm to its status as a beloved street tree.
U. x Accolade™ ‘Morton’ zone 4
U. americana ‘Brandon’ zone 3
U. americana ‘Delaware’ zone 3
U. americana ‘Independence’ zone 3
U. americana ‘Jefferson’ zone 4
U. americana ‘New Harmony’ zone 4
U. americana Prairie Expedition™ ‘Lewis and Clark’ zone 3
U. americana ‘Princeton’ zone 4
U. americana ‘St. Croix’ zone 4
U. americana ‘Valley Forge’ zone 4
U. americana ‘Washington’ zone 3
U. x ‘Arno’*, zone 6
U. x ‘Cathedral’, zone 4
U. x Commendation™ ‘Morton Stalwart’, zone 4
U. x Danada Charm™ ‘Morton Red Tip’, zone 4
U. davidiana japonica ‘Jacan’ zone 3
U. davidiana japonica ‘Discovery’ zone 3
U. davidiana japonica ‘Freedom’ zone 3
U. davidiana japonica (formerly U. wilsoniana) ‘Prospector’ zone 4b
U. x ‘Fiorente’*, zone 6
U. x ‘Frontier’ zone 5
U. x ‘Homestead’ zone 4
U. x ‘New Horizon’ zone 4
U. x ‘Patriot’ zone 4b
U. x ‘Pioneer’ zone 4b
U. x ‘Plinio’*, zone 6
U. x ‘Rebona’ zone 4
U. x ‘Regal’ zone 5
U. x Resista® ‘Sapporo Autumn Gold’ zone 4
U. x ‘San Zanobi’*, zone 6
U. x Triumph™ ‘Morton Glossy’ zone 4
U. x Vanguard™ ‘Morton Plainsman’, zone 4
*Varieties developed for growing in warmer climates (zones 6 to 9) than the usual American elm.
An important element of residential landscaping seems to be going the way of the dodo in modern cities. Tall trees — the big, majestic ones that gave the landscape its character — are increasingly being left out in favor of smaller trees or even shrubs grafted on short trunks.
This is a fairly recent trend. If you look suburban developments over 60 years old, tall tree species dominate. Big maples and huge majestic oaks are everywhere. They helped create an atmosphere of tranquility and well-being. Take a walk in a neighborhood 40 years old or less, though, and you mostly see green lawns and shrubs, maybe a flower bed or two, and a few smaller trees you couldn’t even fit a lawn chair under, but not many larger ones. True enough, a somewhat sparse landscape can be still attractive, but it tends be so in a cold and impersonal way. Such neighborhoods aren’t really inviting. It’s as if the residents planned all along to leave their dreary home landscape on weekends for a break at the cottage … surrounded by tall trees, of course!
Just Don’t Think About It, Plant Them!
Why do larger trees deserve a place in suburban and urban lots?
First, for the shade they offer. Gardeners may complain you can’t grow anything under big trees (actually, you most certainly can: I’ve written an entire book about shade gardening, so I know it’s far from impossible!), but the fact is we’re attracted by shade. During the dog days of summer, a neighborhood well decorated with broad, shade-producing trees is livable; one denuded of any tall vegetation simply is not.
Also, human beings, by their very nature, seem to need trees in their surroundings. Is this a reminder of the long distant past when our ancestors took refuge in trees when they were attacked by predators? No one knows. Still, the feeling of peace and security that emerges from a big tree seems very real. In fact, it can be seen in different cultures all over the world: when people are given a choice of where they would like to live, they inevitably prefer not a forest, but a landscape dotted with mature, tall trees.
Of course, maybe you do feel you have trees on your property. But can you really call a small weeping tree barely 10 feet (3 m) high a tree? Or a flowering crabapple or a Japanese lilac or one of the many other “small trees” so heavily planted these days? They may be trees by definition, but you can’t walk under them without bumping your head, you can’t fit a lawn chair underneath them without your legs sticking out in the hot sun and they don’t create the atmosphere of permanence and security that large trees can provide.
How to Use Trees Wisely
Ideally, to recreate the sense of peace and permanence you want, you’d need at least one large tree per yard. Preferably two, in fact, on in the front and one out back. Obviously, the larger the lot, the more trees it needs.
In addition to the atmosphere they create, big trees offer other advantages:
Reduced cooling costs in the summer;
Reduced heating costs in winter;
Increased land value;
An environment healthier for human physical and mental well-being;
An inviting landscape for our feathered friends;
And much more.
Trees have certain disadvantages, of course, but these are generally easy to overcome.
Planting them, for example, is fairly arduous … but at least you only have to do it once!
The shade they produce will reduce the choice of plants that will grow underneath, but there is still a good choice of shade plants. Where it’s too shady for a dense lawn, for example, there are dozens of equally dense, maintenance-free groundcovers.
Some trees do produce seeds or fruits that can be briefly annoying when they fall, but there are many cultivars that are either sterile or male (male trees produce no seeds).
Finally, there will be leaves to rake up each fall — yes, even so-called evergreens tend to lose leaves at that season —, but fortunately that’s only a once-a-year thing … much less work than maintaining a lawn, which usually requires weekly mowing.
Plant Tall Trees Where They Can Reach Their Full Size
When planning to buy a tree, ask about its maximum height and spread and use that info to find a suitable location. For example, don’t plant it where it can interfere with overhanging wires, too close to the house, or directly in front of a window. Nor should it reach over into a neighbor’s lot, otherwise there is a serious possibility of conflict.
Lots of choice!
What follows are some suggestions of tall trees (over 30 feet/9 m) that can decorate your property. All are low- to no-maintenance trees that will enhance your property’s value.
Note that the trees shown here were chosen for a cold climate region. In areas with more temperate or even warm climate, you’ll have an even greater choice. Measurements are averages reached under normal growing conditions.
Red maple (A. rubrum): Long neglected by arborists, this North American native is becoming more popular, especially in colder climates. Its bark, smooth and pale gray in its youth, becomes rough over time. Its three-lobed leaves turn bright red in autumn. Prefers moist growing conditions. Height: 60 feet (18 m). Spread: 50 feet (15 m). Hardiness zone: 3b. There are also smaller, more symmetrical selections, such as ‘Morgan’ (50 x 50 feet/15 x 15 m) and ‘Red Sunset’ (30 feet x 20 feet/9 x 6 m). ‘Autumn Flame’ (35 x 20 feet/11 x 9 m) is the best choice for colder climates (zone 3).
Freeman Maple (A. x freemanii): This hybrid maple results from a cross between red maple and silver maple (A. saccharinum), but is closer to red maple in overall habit. It’s perhaps even superior to red maple as a city tree and is even a bit hardier: zone 3. There are several cultivars, including Autumn Blaze (‘Jeffersred’), 50 x 30 feet/15 x 9 m), which turns fiery red in the fall.
Sugar maple (Acer saccharum): It used to be that arborists shunned this North American native, considering it unsuited to urban areas, and recommending Norway maple (A. platanoides) instead. Nowadays, attitudes have changed and that there are few situations where a sugar maple wouldn’t be considered a better choice than its Norwegian relative. Planted in isolation, it takes on a beautiful speading, rounded shape quite unlike its fairly scrawny appearance in forested areas. With its excellent orange-red fall color, it’s also much more colorful than Norway maple and less subject to winter damage. Plus its smaller, rapidly decomposing leaves have less tendency to choke out grass. Finally, it isn’t subject to tar spot disease, this disease which turns the leaves of Norway maple into an unsightly mess. Both, however, do have dense and shallow roots: there’s no denying that maintaining a perfect lawn under either maple is a challenge, though. Height: 60 ft (18 m). Spread: 40 feet (12 m). Hardiness zone: Zone 4. There are several horticultural selections, including ‘Green Mountain’ and ‘Legacy’, which offer a more regular habit on a somewhat smaller tree than seed-grown sugar maples.
Common Hackberry (Celtis occidentalis): This North American tree looks a bit like an elm but with a more rounded crown. Corklike bark. Yellow color in autumn. Height: 65 feet (20 m). Spread: 50 feet (15 m). Hardiness zone: 4.
Ginkgo (Ginkgo biloba): Very slow growing, but totally resistant to insects and diseases. Attractive yellow foliage in the fall. Always ask for a male specimen: the females drop messy, stinky fruits. Height: 45 feet (14 m). Spread: up to 40 feet (12 m), but much narrower than wide for the first 60 years or so. Hardiness zone: 4.
Honey Locust (Gleditsia triacanthos inermis): Tree with an open, often irregular crown that lets sun through. Rough bark. The compound leaves are composed of leaflets so small that they decompose quickly: you don’t even have to rake them up in the fall! The extremities of the branches often freeze during the winter in colder climates, but that doesn’t really affect its appearance. Look for the cultivars ‘Moraine’ and ‘Skyline’, as several honey locusts, like ‘Sunburst’, are too small to make good shade trees. Height: 65 feet (20 m). Spread: 35-55 feet/10-17 m. Hardiness zone: 4b. ‘Northern Acclaim’ is an extra-hardy variety: zone 3.
Amur Cork Tree (Phellodendron amurense): Little known, but very attractive and virtually without cultural problems. The bark on mature specimens is very corklike. Height: 40 feet (12 m). Spread: 40 feet (12 m). Hardiness zone: 3.
Siberian Pear (Pyrus ussuriensis): A large tree that dwarfs its smaller fruit tree cousins: apples, plums, cherries, etc. It’s also essentially immune to most of the diseases and insects afflicting fruit trees. It blooms abundantly in spring, covering itself with white blossoms, but its tiny fruits are of no interest to humans, although they do attract birds and small mammals. It will only bear fruit if there are two different clones in the area, since cross-pollination is obligatory for this species. Height: 40 feet (12 m). Spread: 33 feet (10 m). Hardiness zone: 3.
Oaks (Quercus spp.): A large group of trees, most tall and spreading, generally with toothed leaves. They’re considered among the most majestic of trees, but their growth is fairly slow, at least after the first 10 years or so. Height: 65 feet (20 m). Spread: 50 ft (15 m). Hardiness zone: generally, zone 4. Red oaks (Q. rubra) and scarlet oaks (Q. coccinea) are particularly interesting for their massive shape and fall color. Where space is limited, consider columnar English oak (Q. robur ‘Fastigiata’) which reaches the same height as the other oaks but rarely exceeds 13 feet (4 m) in diameter. The best oak for cold climates is bur oak (Q. macrocarpa), hardier than the others: zone 3. Shingle oak (Quercus imbricaria) is unusual among hardy oaks in that it has narrow untoothed leaves.
The following trees may be useful in some cases … but have problems that can seriously reduce their usefulness under certain circumstances. It’s up to you to decide whether they are worth growing under your conditions!
Horse Chestnuts, Hickories, Walnuts (Aesculus spp,. Carya spp., Juglans spp.): They make beautiful trees, but their large fruits can be an annoyance, especially near roads. In addition, walnut trees are allelopathic (toxic to plants that grow at their base).
Birch (Betula spp.): Most make very nice trees, with attractive bark, but they’re often short-lived (especially silver birch [Betula pendula] and its varieties) and rarely make it to their full size. In addition, they are susceptible to a wide range of diseases and insects and that can mean a lot of spraying … under some circumstances. Ask a local arborist their opinion, as the problems tend to vary greatly, from minor to major, depending on local conditions. One exception is river birch (B. nigra), especially the cultivar Heritage (‘Cully’), with bark that exfoliates gracefully: it’s long-lived and disease- and insect-free under most conditions. Height: 50 feet (15 m). Spread: 35 feet (10 m). Hardiness zone: 3.
Catalpa (Catalpa spp.): Although catalpas survive in cold regions and thus some nurserymen rate them as zone 4 trees, in fact, they tend to suffer severe winter damage in zones 4 and 5, at least periodically, and, as a result, grow very irregularly. With their abundant white to lavender blooms, they make an excellent choice in areas 6 and up, though. Height: 50 feet (15 m). Spread: 30 feet (9 m).
Linden (Tilia spp.): Tree with a strong trunk and heart-shaped leaves, plus highly scented flowers. The little-leaved linden (T. cordata) is very popular and offers many interesting cultivars, however … this genus is not a good choice in regions infested with Japanese beetles, as they literally defoliate the tree every summer. Height: 100 feet (30 m). Spread: 80 feet (25 m). Hardiness zone: 3.
Elm (Ulmus spp.): American elm (U. americana) almost inevitably falls victim to Dutch elm disease, which is difficult and expensive to fight. There are, however, several elms, including hybrid varieties, which share the American elm’s majestic upright spreading habit while showing good resistance to the disease. Before buying an elm, always ask if it’s resistant to Dutch elm disease. The Siberian elm (U. pumila) is resistant to Dutch elm disease, but is a weak-wooded tree with a poor growth habit and susceptibility to other diseases. Plus it self-seeds excessively and is considered an invasive species in many areas.
Trees to Avoid at All Costs
Ash (Fraxinus spp.): The arrival of the emerald ash borer (Agrilus planipennis), a deadly tree-piercing insect, in North America—and even now in Europe—has killed pretty much any interest in this formerly popular street tree. You might want to maintain the ones you have, but it’s probably wise to avoid planting new specimens.
Poplars, Willows, Silver Maple (Populus spp., Salix spp., Acer saccarhinum): The roots of these fast-growing trees are extremely invasive and often cause damage to domestic and municipal water and sewage pipes. They often also sucker extensively or self-sow and so become very invasive. It’s illegal to plant these trees in most municipalities.
There you go: a list of big and beautiful trees you might want to consider growing. And don’t delay, as it will take a few years before you can savor their full effect on your property!
The weeping willow (Salix x sepulcralis ‘Chrysocoma’) may be a good choice for an urban park, but don’t plant it near a house.
I regularly get questions from home owners worried by the presence of a tree near the foundations of their house or near water or sewer pipes. Usually, however, there is no problem unless the tree is so close to the foundation that its trunk or branches actually rub against it.
Pipe clogged with silver maple roots (Acer saccharinum).
However, there are are a few trees that should not be planted near a house or underground pipes. These trees have roots that are long and invasive and are known for their ability to block drainage pipes, invade septic tanks and work their way into the cracks of a foundation and thus damage the house. In many municipalities, it is in fact illegal to plant these trees… which doesn’t stop local garden centers from selling them! Check before planting any of the following trees and If you are allowed to plant these trees, plant them at least 100 ft (30m) from any building, pipe, drainage system or septic tank.
Here is the short list of culprits for temperate climates:
American elm (Ulmusamericana) Zones 3-8
Poplar (Populus spp.) Zones 2-7
Silver maple (Acer saccharinum) Zone 2
Willow (Salix spp.) Zones 1-10
Note that the shrub willows pose no problem; it is the tall tree willows that are harmful.