The cost of routine mowing along North Carolina's approximate 300,000 acres of roadside turf amounts to the considerable sum of $16 million per year. Unfortunately, mowing is an unavoidable part of vegetation management. However, roadside vegetation manag
Today's grounds manager can choose from among many woody and herbaceous ornamentals to use within the landscape. Arboreta, botanical gardens, plant propagators and breeders constantly bring new and improved plants to the industry. This has created a huge number of available selections and choices for all geographical areas within the United States.
Recently, choosing plants based on site analysis--"the right plant for the right place"--has received much emphasis. Horticulturists, designers and architects use factors such as plant size, resistance to prevalent insects and diseases, and tolerance to climatic factors (wind, snow and ice, temperature) in addition to ornamental characteristics to select plant material. With such an array of material from which to select, this shouldn't impose any serious limitations. You can omit species with serious drawbacks without sacrificing diversity or aesthetics in your design.
However, just because some plants have serious drawbacks does not mean they are no longer available or planted.
* People tend to stick with plants with which they are familiar, so they still plant some species in spite of their known flaws. Designers may include such species to appease clients that request them.
* Some plants may seem to be "the right plant for the right place" because they are tolerant of site factors. However, you soon find they actually are too successful, aggressively invading surrounding areas or dominating adjacent plants.
* Plants may be ideal in most respects but suffer chronically from a particular pest or disease that, if not life-threatening, simply renders the plant unattractive, forcing you to choose between constant treatments or unattractive plants.
In the following discussion, I list some ornamentals that exhibit problems serious enough to warrant deleting them from your selection list. In some cases, problems that are somewhat serious but not severe still may justify avoiding the species due to the fact that it has been overused and that aesthetically equivalent but less-demanding substitutions exist. In most instances, certain regional exceptions to a plant's susceptibility to pests, diseases or environmental conditions exist. Therefore, this (and every other plant list) cannot apply universally--you must use your experience, common sense and knowledge of local conditions. Further, it is far from complete. But it will give you an idea of the kinds of plant qualities that can cause maintenance headaches.
Deciduous trees * Acer platanoides--Norway maple. Introduced from Europe, this species has been widely planted as a street tree and in open lawns in residences, parks and commercial sites throughout the country. As a street tree, it often is unable to withstand urban stresses and thus declines, requiring drastic corrective pruning. Plus, its roots are shallow, causing difficulty for herbaceous ground covers growing beneath its canopy. With the introduction of so many other fine maples--Acer truncatum (Shantung maple), Acer triflorum (three-flowered maple) and Acer ginnala (Amur maple), to name a few--you should avoid the Norway maple.
* Acer saccharinum--silver maple. Silver maples, also widely used, turn into potential liabilities with age as their brittle limbs become prone to breakage during storms. This species also is susceptible to a host of diseases and pests, such as anthracnose, verticillium wilt, cankers and aphids. Nurseries continue to offer silver maple because of its fast growth and easy culture, but with all the problems this species poses, you're best to steer clear.
* Platanus occidentalis--American sycamore. This native hardwood grows in low-lying, wet areas with a natural range that covers most of the eastern half of the United States. Where I live in New Jersey, and in many other regions, it is a common street tree. Unfortunately, it is highly susceptible to anthracnose. Thus, by mid-September, in many parts of the United States, sycamore leaves cover streets and sidewalks. Plus, as it matures, the bark begins to peel and can become quite a nuisance as it litters the ground. Due to these problems and the fact that it has been overplanted in many locations to the point of reaching monoculture status, you should make other selections and introduce some diversity into the landscape.
* Ginkgo biloba--maidenhair tree. The many improved cultivars of this species are excellent selections for use in cities and public parks. One important characteristic of the better selections is that they are males (Ginko biloba is dioecious--it has separate male and female plants). However, nurseries sometimes offer the "straight" species, which can be female. It is important to avoid planting females because the fleshy covering of the seed (borne only on the females) is messy and has a powerful, foul odor. I first encountered this several years ago when walking an old estate. I cameacross an unpleasant smell and, after looking down and then up, I realized I had walked under a female Ginkgo tree.
* Betula populifolia--gray birch. Naturalized throughout New England as far south as the Mid-Atlantic states, this tree has no place in a landscape setting because of its susceptibility to leaf miners, cankers and bronze birch borers. Leaf miners cause early leaf defoliation with trees becoming completely bare by June in New Jersey. Borers arrive when the tree undergoes any environmental stress, making this a short-lived and unwelcome ornamental tree.
The same warning applies to several other birches, including the popular European birch (Betula pendula). Pests, especially borers, rapidly disfigure or kill these trees without ongoing control measures. Before using a birch, learn about pests or diseases that occur in your region and then select a species that is resistant to them. River birch (Betula nigra) is one popular species with relatively few problems.
Conifers * Picea pungens--Colorado spruce. Native to the Southwestern United States, this conifer thrives on limited rainfall and calcareous soils. Because of its blue needles--unmatched by any other conifer--it is used extensively east of the Mississippi River, where rainfall is abundant and the soils are acidic. Unfortunately, these conditions cause it to be a short-lived tree in the East, prone to problems such as Cytospora canker, spruce-gall adelgid and spruce budworm. When looking for alternatives, consider Serbian spruce (Picea omorika) and white fir (Abies concolor), which have softer blue needles and are underused in the landscape.
* Pinus nigra--Austrian pine. The widely used Austrian pine commonly succumbs to Diplodia tip blight, which causes severe dieback and sometimes kills the entire tree (see photo, at left). I have seen isolated specimens sited where early morning sun dries the dew that has formed on the needles. This alters the environmental conditions necessary for infection to occur. However, with so many other available pines such as limber pine (P. flexilis), white pine (P. strobus) and lacebark pine (P. bungeana), the Austrian pine is not the best choice.
Flowering trees * Malus--flowering crabapple. Crabapples suffer from three serious diseases: fireblight, cedar-apple rust and apple scab. I am a great admirer of these trees, which people value for their early spring flowering and fall and early winter fruit display. However, you should avoid certain cultivars that are susceptible to these diseases. These include 'Pink Perfection', 'Dorothea', 'Henry F. Dupont' and 'Van Eseltine'. Fortunately, cultivars with resistance to one or more of these diseases are available, and these will save you a great deal of effort combating these diseases.
Check with your nursery or an extension horticulturist for cultivar recommendations for your area.
* Pyrus calleryana 'Bradford'--Bradford pear. It's amazing to see nurseries still offering this selection of the callery pear, even in areas where it clearly is unsuited. Widely planted as a street tree during the 1970s, problems began to occur as the trees matured. Because of their acute, narrow crotch angles, Bradford pears are highly susceptible to splitting, a common sight after an ice storm or high winds (see photo, page 66). Although this species is virtually free of disease or insect pests, I recommend planting another pear selection such as 'Aristocrat', 'Chanticleer' or 'White-house', which have better branching structure.
* Magnolia x soulangiana--saucer magnolia. When selecting ornamental plants, designers try to make selections that have more than one season of special interest. The saucer magnolia has just one: the emerging spring flowers (which can be spectacular). Nurseries always offer this small specimen tree for early spring sales because of its beautiful bloom. However, if a late spring frost occurs--as it often does--it will destroy the emerging flower buds (see photo, at right). In some parts of the country, frost destroys the spring bloom three out of every four years. Keeping this in mind, you'll derive little value by adding this ornamental to your plant palette unless you are in an area that's usually free of damaging spring frosts.
Ornamental shrubs * Euonymus japonica--Japanese euonymus. This introduction quickly gained popularity because of its versatility as a wall climber, ground cover or shrub, and its cultivars with colorful foliage. However, it is highly susceptible to crown gall, aphids, leaf spots, powdery mildew and, most importantly, scale. Although you can control many of these pests with applications of horticultural oil, this plant requires monitoring and periodic control measures. It's best to avoid this species and choose Euonymus kiautschovica (spreading euonymus) in its place.
* Photinia x fraseri--Fraser photinia. This is the most popular Photinia and widely planted in much of the United States. It is another example of a good thing gone bad. Overplanted as a large hedge for privacy screening, it has developed several pest problems. One is a leaf spot, Entomosporium maculatum, which is a tremendous problem and can completely defoliate plants. Breeders are working to combat the leaf-spot problem with new resistant varieties, but until they are available, you should choose more trouble-free shrubs.
Ground covers * Aegopodium podagraria 'Vari-egatum'--Bishop's goutweed. Unless you have a confined area to restrict spread, you may never get rid of this plant once you've established it. This perennial vigorously spreads by underground rhizomes. In a mixed grouping, it easily can spread over other plants. To make matters worse, when humidity rises in the summer, it is susceptible to a severe leaf blight that can completely defoliate the plant. It won't regenerate until late summer when drier, cooler air returns.
* Juniperus horizontalis 'Bar Harbor'--creeping juniper. This selection was discovered growing in Maine where it inhabits crevices in rocks exposed to drying winds and salt spray, and this is the ideal habitat for this plant. Unfortunately, in a more moist, humid climate or under irrigation, it is susceptible to two diseases. The first is Phomopsis tip blight, which occurs in early spring. The second is Kabatina blight, which occurs in mid-summer. In the proper (xeric) environment, 'Bar Harbor' juniper is an effective plant. Otherwise, select another species of juniper such as J. chinensis, which offers many cultivars resistant to these two diseases.
Herbaceous perennials * Aquilegia flabellata--columbine. This versatile perennial is suitable for full sun to partial shade and blooms in late spring with nodding flowers in a variety of colors. The beautiful compound foliage is blue-green and glaucous and borne on long petioles. Once columbine finishes flowering, its attractive leaves provide continued enjoyment. Unfortunately, columbine is prone to many pests including borers, crown rot and, especially, leaf miner. Leaf miners don't seriously harm the plant, but they disfigure the foliage that is such a large part of the plant's appeal.
* Oenothera speciosa--showy primrose. This, like Bishop's goutweed, is an example of a perennial that you must confine, especially in ideal growing conditions (fertile soil and ample moisture). Native to Mexico and much of the United States, it's a sprawling plant with showy white to pink flowers that blooms in summer. However, it can run rampant and competes aggressively with other plants.
Know your plants
It actually is quite difficult to create a list of plants that are undesirable for the landscape in all circumstances: plants that are prone to certain insects or diseases nevertheless may be excellent choices in regions where such pests are not common; frost-tender plants obviously are acceptable in warm-winter regions that are largely frost-free; and aggressive species have their place too. In other words, exceptions always exist. It's up to you to use your knowledge and judgment to decide what's appropriate.
When choosing plants for the landscape, keep in mind that you have an abundance of options with multiple aesthetic attributes and minimal maintenance problems. Choose these over those that are one-dimensional or that have reputations as being problematic. (Or, at least realize what you are getting into!) You'll find that your designs are not only more trouble-free, but also more diverse and interesting as well.
Bruce C. Neary is owner of BCN Horticultural Consulting Services (Bricktown, N.J.).
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