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Trees to Reconsider Before Planting

All tree species have positive and negative traits. There are some species of trees that may be the only species that will grow under certain conditions. Some of the trees described below are listed as acceptable trees, but they do have some traits that can make them a nuisance in certain situations. There are some species of trees that have many negative traits that make them a poor selection for any site. These tree species will be discussed so that you might be better informed before you plant.

Aspen — Quaking and Swedish

Populus tremulus and Populus tremuloides

There are few things more beautiful than an aspen grove, especially in autumn. Aspen are a fabulous species in Utah above 6000 feet in elevation and on north facing slopes. However, aspen will not thrive in residential applications in the valleys.

Natively, aspens grow in large groves. These groves are one very large plant that has an enormous root system and many stems. Aspen are genetically programmed to grow this way. Aspen in the valley will try to grow this way also; they will not survive as a single stem tree. Aspen have a very long list of insects, bacteria, and fungi that constantly attack the trees. This is why they produce so many stems. The same elements will attack aspen trees in the valley.

If aspen trees are planted in the valley, they will produce shoots from their roots wherever the roots may grow, they will be attacked by many pests, they will be covered by aphids in the spring, the leaves will turn yellow and brown in the summer, the bark will weep, and they will die while young. Swedish Aspen are prone to the same situations that Quaking Aspen are and will react in the same manner. Aspen should be enjoyed in the mountains and not attempted in the valleys.

Box Elder

Acer negundo

Box Elder is one of Utah’s native tree species. They are most often found in the mountains and foothills, but they can also be found in valley locations where there is adequate water. Box Elder trees are inherently weak trees and are prone to rot. Box Elder trees are prone to profuse succor growth. The seeds of Box Elder trees are the main food source of Box Elder Bugs, which can be a profound nuisance. Box Elder trees are very susceptible to Verticillium Wilt, a tree fungus that is common in most Utah soils. If you plant a Box Elder tree, you can expect it to be short lived; it will tend to lose branches in strong wind storms, have plenty of succors and erratic growth, and, if affected by Verticillium Wilt, die suddenly. There are many other Maple species that are better choices for any landscape.

Colorado Spruce

Picea pungens

Colorado Spruce is one of the most popular evergreen trees in Utah landscapes. Colorado Spruce will grow in most areas of Utah, and in most soil conditions. Colorado Spruce can have color that ranges from dark green to bright blue. A Colorado Spruce can obtain heights of over 60 feet and widths of 30 feet or more.

There are some issues with Colorado Spruce that should be considered before planting. Colorado Spruce need plenty of room to grow, so most residential landscapes may not be large enough to accommodate this species. Colorado Spruce, along with all other spruces, produces chemicals that will kill any other vegetation that tries to grow under the canopy of the tree. Most importantly, Colorado Spruce has a very dense crown that tends to catch the wind like the sail of a ship. In high winds, especially microburst type winds, Colorado Spruce are very prone to blow over. Colorado Spruce can produce a high risk situation if it is planted near a home or other structure.

Flowering Pear

Pyrus calleryana

Flowering pears produce large amounts of white blossoms in the spring that put on quite a show. They also have a fantastic deep red fall color. Flowering pear can be easy to find in most nurseries and can adapt to many growing situations. This species has become quite popular over the past couple of decades and can be found in most urban landscapes.

The main consideration with flowering pear is their growth habit. Flowering pear branches attach at a very narrow angle from the trunk. As the branch and trunk increase in diameter, they push against each other. Eventually, flowering pears push themselves apart.

Flowering pears naturally hold on to their leaves as late as December. When the snow falls on the branches that still have their leaves, the branches are torn from the trees. Flowering pear are very prone to fire blight, a fungus disease that can quickly kill the tree. Because of these issues, many arborists discourage the planting of flowering pear. If they are planted, they tend to not live more than 10 to 15 years.

Flowering Plum

Prunus cerasifera

Flowering plum in the spring produce one of the more spectacular flower shows. The bright pink and burgundy blossoms can be stunning. Flowering plums have purple leaves that remain through the summer. The species can be adaptable to most growing conditions and do not need high amounts of water. These traits have made flowering plum a popular species of ornamental trees.

There are a couple of traits of flowering plum that should be considered before they are selected. Flowering plums have a great tendency to produce succor sprouts all through the canopy of the tree which will require higher levels of maintenance to keep the tree with a healthy growing habit. Flowering plums are not large growing trees and tend to be lower branched. The low branches can be cumbersome to mow around and makes them unacceptable as street trees. Flowering plums tend to have weak branch attachments and can push themselves apart as they grow.

Green Ash

Fraxinus pennsylvanica

Green Ash was a very popular species in Utah for a long time. Green Ash will grow in many Utah locations. The problem with Green Ash is overpopulation. The result of having so many Green Ash trees in our urban forests is that most mature specimens have become infected with borers. The borers slowly consume the growing tissues of the trees, and eventually kill them. While this process takes place, the stems and branches of the trees tend to become brittle and fall out of the tree. Treatment for borers can be expensive and must be maintained over a period of many years. There are other species of Ash that are less susceptible to borer problems (White Ash, Blue Ash, Raywood Ash, and Flowering Ash) that should be considered before Green Ash.


Morus alba and Morus rubra

Mulberry is very popular in some areas because of their adaptability to difficult sites and their rapid growth rate. Mulberry comes in weeping and contorted forms that many people find attractive. Most Mulberry come as fruitless varieties. Mulberry have very interesting shaped leaves that will stay on the tree until one day in the fall when the entire tree will drop all of its leaves. In several respects, Mulberry can be a good selection.

The points to reconsider about Mulberry are pollen, surface roots, succor growth, and fruit. Fruitless Mulberry is a male form of the species. Although these trees do not produce fruit, they do produce an amazing amount of pollen. Mulberry has been determined to be one of the worst pollen producers and can be nearly hazardous to those that have allergies. Mulberry tends to have large roots that grow near to or above the surface of the ground which can be detrimental or hazardous in some landscapes. Mulberry also produces many succor sprouts in their canopy which can require higher levels of maintenance. Mulberry fruit is very dark in color and capable of staining any surface that it lands on. For these reasons, Mulberry may not be the best choice for a landscape.

Norway Maple

Acer platanoides

Norway Maples are one of the most popular trees in Utah landscapes. Norway Maple is very adaptable to most growing conditions and locations. Because of its adaptability and availability, Norway Maple has become one of the most overplanted species of trees. In Springville, Norway Maple makes up more than 60% of our urban forest. This overplanting can create many disease problems that could devastate our urban forest. For these reasons, it is suggested that we don’t plant more Norway Maples.

Poplar/Cottonwood Trees

Populus spp.

Poplar and Cottonwood trees are fast growing trees that love to be near water. Many Poplar trees can grow 5 feet or more per year. Many people choose to plant poplar trees so that they can have quick shade in their new landscapes. However, it is this rapid growth rate that contributes to the negative points of poplar trees.

Poplar and cottonwood trees are very short lived trees that have weak wood and poor structures. Most poplar trees, even cottonless forms, also can produce pollen and catkins that can be quite messy in the spring. Poplars, because of their love of water, tend to grow roots near or above the soil surface. Poplars will send up shoots from their roots profusely, especially in well irrigated landscapes. Because of their weak wood, poplars are prone to fall apart in storm events. Poplars may have use and windbreaks in rural areas or on farms. However, Poplars should not be included in a residential landscape.

Russian Olive

Elaeagnus augustifolia

Russian Olives were imported to Utah decades ago because they can grow in almost any situation. This tree has proven that it can grow in even the worst circumstances. It is a very hearty tree that is very hard to kill once established. Russian Olive is also very successful at quickly populating any area where it might be growing.

Most people dislike Russian Olive because of its profuse and long thorns, its very numerous fruit, its pungent odor as it flowers in the spring, and its ability to quickly overtake any area where it may grow. One established, Russian Olive can be very hard to eradicate because of its ability to sprout from roots as well as seeds that can last in the soil for several years. In some areas, Russian Olives are considered a noxious weed.

Siberian Elm

Ulmus pumila

Siberian Elm is the weed of the elm family. While most elm species are good hearty trees, Siberian Elm is a problem in the urban forest. Siberian Elm are prone to having weak wood, slime flow from bacteria, poorly attached branches, and producing amazing amounts of seeds. In many areas, Siberian Elm has become an invasive species and a noxious weed. Most people do not plant Siberian Elm; they are very talented at planting themselves. Even on the poorest sites, there are better selections than Siberian Elm.

Siberian Elm is not the same species as Chinese Elm or Lacebark Elm. Chinese Elm or Lacebark Elm is a very hearty species of elm that is highly recommended for many Utah sites. The bark and growth habit of Chinese Elm is very different from Siberian Elm and should not be confused as the same tree species.

Silver Maple

Acer saccharinum

Even in their native habitat in the Midwest, Silver Maple is considered to be a less desirable tree. In Utah, Silver Maple tend to be chlorotic (have very bright green or yellow leaves), short lived, and weak. Most Silver Maples don’t live very long in Utah soils. A Silver Maple that does survive tends to lose its leaves early, drop branches and twigs consistently, and fall apart in storms. Silver Maple is not a very good selection. There are many other maple species to choose from.

Tree of Heaven

Ailanthus altissima

Invasive Species

Tree of Heaven, sometimes referred to as Sumac Tree, is considered a noxious weed and/or an invasive species in many areas. Tree of Heaven is a very rapid growing tree that can grow in almost any location. Tree of Heaven will produce thousands of seeds that will spread very quickly to many locations. There are many areas of the USA where Tree of Heaven are taking over native forests. Tree of Heaven tend to have weak wood, weak branches, and roots that grow near the surface. If you have a Tree of Heaven, you should remove it immediately and plant an acceptable species.

Willow Trees

Salix spp.

All species of willow trees share the same negative traits. Most notable of these traits are very weak wood, rapid decay of the trunk and branches, and the habit of constantly dropping branches and stems. Willow trees are short lived trees that want to be very near water. People tend to choose willow trees because of their rapid growth rate. However, as with poplar and cottonwood, rapid growth results in some inherent problems. Willow trees have their uses, but residential and commercial landscapes should not be one of them.

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