Leyland Cypress (x Cupressocyparis leylandii)
Zone 6 to 10
This tree has so many negative characteristics, its success is truly a testament to the nursery industry's marketing efforts. Granted, it grows very rapidly, eventually reaching a height of 70 feet or so. However, with a life expectancy of only 25-35 years, it essentially starts to decline just as it's reaching its full height, and it is susceptible to a host of insect and disease problems. Bagworms are a major issue, requiring either hand-picking or spraying with an insecticide-and either hand-picking or spraying a 50-foot tall tree is a major (and expensive!) undertaking.
Diseases affecting Leyland cypress includ seiridium canker, botryosphaeria canker, cercospora needle blight, and a variety of root diseases. And think about it: Does your home landscape really need a hedge the height of a five-story office building? Compounding the problem is the fact that people often plant large numbers of these trees as monoculture screens, which means that whatever affects one plant will likely affect all of them. To add insult to injury, some salespeople cheerfully suggest planting these trees twice as close together as they should be planted, saying, "You can always take out every other tree when they get crowded," and you have a recipe for disaster. This is the source of the largest number of tree problem calls to our Extension Master Gardener Volunteer office Information Line.
Bradford Pear (Pyrus calleryana 'Bradford')
Zone 5 to 9
Bradford bear is the source of the second largest number of problem calls. This is a lovely tree: the spring bloom display is breathtaking, the overall shape is exceptionally symmetrical, and the fall color is glorious. It grows rapidly to 30-50 feet, with a spread of 20-35 feet, and it tolerates a range of soil conditions. Unfortunately, its branching structure leads to large branches or whole sections of the tree simply splitting away from the trunk during winds or ice/snow events. At that point, its highly symmetrical profile is no longer even remotely symmetrical; since they're often planted in matched sets lining a driveway, the beauty of the entire planting is irrevocably damaged. They are also, unfortunately, an invasive plant in many areas of the country. To top things off, Bradford pears have a fifteen-year life expectancy-essentially making them "disposable" trees. Avoid at all costs.
Walnut (Juglans nigra)
Zone 4 to 9
Black walnut is a beautiful tree, reaching a height of 75-100 feet, with a spread to match. It tolerates drought and rabbits, provides edible fruit, and makes a lovely shade tree. Unfortunately, its roots produce chemicals called juglones, which are highly toxic to a wide range of desirable landscape plants (azaleas, rhododendrons, blueberries, peonies. tomatoes, peppers, and potatoes). Additionally, the husks of the nuts can stain clothing and sidewalks, so unless you have a really large landscape that will allow you to give this tree its own space, you'd do well to stay away from black walnut.
White Mulberry and Red Mulberry (Morus alba, Morus rubra)
Zone 4 to 8
Growing to 35-50 feet, with a spread of 35-40 feet, these are attractive, easily grown trees with interesting foliage and edible fruit. Their fruit is very attractive to birds, they tolerate a variety of growing conditions, and they naturalize well (and are, in fact, native to much of the country). However, both of these trees have weak wood and very weedy seedlings; white mulberry is invasive through much of the country, while the fruit of the red mulberry is very messy and will stain clothing and patios. Borers, whiteflies, bacterial blight, coral spot canker, bacterial leaf scorch, powdery mildew, root rot, and witches broom are a few of the other problems that can affect the trees, along with scale, mites, and mealy bugs. All in all, best to give this one a wide berth.
Sycamore (Platanus occidentalis)
Zone 4 to 9
Sycamore can be a magnificent specimen, growing 75-100 feet tall and wide, with a trunk diameter easily reaching 8 feet, characterized by mottled, exfoliating bark. Sadly, it is prey to sycamore anthracnose, a significant disease that can severely damage the tree. Canker, leaf spot, powdery mildew, borers, scale, Japanese beetles, caterpillars, and mites all afflict sycamores. More important to homeowners, though, is the fact that litter from the leaves, twigs, bark, and fruiting balls pose significant problems in terms of maintaining a neat landscape. With so many marvelous trees available that don't have these problems, why invest in this one?
White Pine (Pinus strobus)
Zone 3 to 8
White pine is a moderate-sized tree, reaching a height of 30 to 40 feet and a spread of 7-10 feet. Unfortunately, it is affected by white pine decline, which causes needle discoloration and browning, shriveled bark, oozing sap, and, in some cases, death. It's also vulnerable to injury from salt spray, ice damage, and winter burn, and it's susceptible to ozone damage, an increasing threat in urban/suburban areas. White pine is also much loved by bagworms and yellow-bellied sapsuckers. Again, why plant a tree that you know is prone to this many problems?
Birch (Betula spp.)
Zone 4 to 9
Several varieties of birch are lovely landscape plants; a few sport dramatic exfoliating bark. In addition, many thrive in wet environments; avoid planting in a hot, dry location, and aim for afternoon shade. Generally reaching 40-50 feet, occasionally available as a clumping tree with 3-5 stems, birches, particularly river birch (Betula nigra), are popular landscape plants. Many birch varieties are susceptible, though, to the bronze birch borer, a tree killer, and they have a very shallow root system that can be easily damaged by soil disturbance. Birch leaf miner is another significant problem, and control requires spraying, which is time-consuming and costly. Not a tree to be avoided at all costs, but think carefully before planting.
Lombardy poplar (Populus nigra)
Zone 3 to 9
Avoid this tree at all costs. Characterized by a very tight columnar shape, the Lombardy Poplar can exceed 100 feet in height within 20 to 30 years. However, at that point, it's also reached the end of its life expectancy, so it's another "disposable" tree as opposed to a permanent landscape addition. Lombardy poplars have structurally weak branches that break easily when stressed by wind, snow, or ice. Leaves and branches shed, causing sanitation issues in a home landscape. Roots can invade sidewalks and damaged sewer lines. There are few redeeming characteristics other than its rapid growth rate. Save your money and invest elsewhere.
Norway Maple (Acer platanoides)
Zone 3 to 7
An easily grown tree, Norway maple will reach 40 to 50 feet in height with an almost equal spread, and it tolerates air pollution and drought quite nicely. It has a few problems (verticillium wilt, which can be fatal, as well as sunscald and cracking of the bark), but the a more significant issue is its thick leaf canopy and shallow root system that severely limit what can be planted within the tree's drip line. Combine that with the fact that Norway maple is considered invasive in ever-widening areas of the country, and it adds up to another tree to avoid.
Empress Tree (Paulownia tomentosa)
Zone 3 to 8
Native to Central and Western China, the "royal empress tree" (it's marketed under a variety of names) bears strikingly large leaves and showy, fragrant flowers on a frame that grows 30-40 feet tall and wide. Unfortunately, its wood is weak and subject to breaking, and the tree, marketed as "easily propagated," is so easily propagated that it's become invasive in much of the eastern half of the country. We don't need more of these planted; they're spreading quite nicely on their own without our assistance.
Mountain Ash (Sorbus americana)
Zone 3 to 7
A lovely tree that will grow to around 30 feet, with a spread of perhaps 15 feet, the mountain ash is a good food source for a variety of wildlife. That's all good, but the list of potential problems includes borers, aphids, sawflies, scale, mites, fire blight, rust, and scab. Cankers, crown gall, and powdery mildew may also attack. Seriously now: do you want a tree with this many potential problems in your landscape?
Mimosa Tree (Albizia julibrissin)
Zone 6 to 9
Native to Iran and Japan, the mimosa tree is a lovely, delicate-looking tree with fern-like foliage and showy, powder-puff-like pink blooms. It tolerates high temperatures and a wide range of soils, including high alkalinity. It grows rapidly to 20-40 feet, with a striking vase shape that makes it a lovely accent tree for a home landscape. Those are all strong positive attributes, but the Mimosa is susceptible to a serious wilt problem, as well as mimosa web worm. More significant to homeowners, though, is the fact that it is a prolific self-seeder, so you rarely have "just one" Mimosa. The wood is weak, and is often damaged in storms. To top it all off, most folks plant it near the house so they can enjoy its lovely flowers from a patio, and as the blooms fall, they (and the leaves and seed pods) drop onto the patio, where they become a significant housekeeping issue. Best to enjoy this plant in someone else's landscape.
Austree (hybrid between Hankow willow [Salix matsudana] and white willow [Salix alba])
Zone 2 to 9
If you're looking for a temporary windbreak or an erosion control solution, this could be your tree. It will never be a suitable shade tree, thought, and experts recommend planting it-if at all-along with more "permanent" trees if you're using it in a windbreak or screening application. The hybrid Austree will, indeed, grow up to 10 feet annually in moist sites, reaching a height of 35-45 feet and up to 30 feet in width. "Live fast, die young," though, applies to the Austree. Like most fast-growing trees, it has extremely weak wood that is very susceptible to storm damage, and it drops leaves and small branches non-stop. Add to that its susceptibility to disease and insect problems, and you have a tree with very limited application and desirability.
