Shrub Selection for Utah Landscapes
April 2010 | Horticulture/Landscapes/2010-01pr
Urban and suburban landscapes present special challenges concerning shrub selection in Utah. Due to our distinctive climate, shrubs must be able to withstand intense sunlight, low relative humidity, drying winds, and limited seasonal precipitation. Additionally, landscapes may also have shady locations and areas of high moisture that create unique situations. This means that ideally before purchasing shrubs, a person should research suitable species adapted to the specific location where they will be planted.
Even with the unique conditions that challenge shrub species, many still perform well and should be used more often in the landscape. They soften architectural structures, provide screens for privacy, and add unique variety to the landscape with their various forms, colors and textures.
Shrubs and Site Selection
Shrubs live longer than many other landscape species and are a greater investment of time and money. One of the most effective ways to protect these investments is to plant them in the right place the first time. This means surveying the yard and assessing the different factors that could ultimately affect the long-term survivability of the plants. It is much easier to choose the right shrub for specific conditions than it is to try to modify those conditions for the shrub.
Factors to consider include mature shrub size and form, soil conditions, available moisture, temperature, sun exposure, wind exposure, and overall intended use or purpose of the plants.
The most important, and often most overlooked, attribute of shrubs is their size at maturity (height and width). Shrubs planted near a house or building, particularly beneath windows or awnings, should be a smaller size at maturity so as to not to block views or cause damage to property.
For example, Rhus typhina (staghorn sumac) is a shrub used for a wide variety of urban
conditions, but its size potential (15 to 25 feet) makes it a poor choice for placement
near the house. A similar species, Rhus aromatica ‘Gro-Lo’ (Gro-Lo fragrant sumac),
would be an acceptable alternative
because its mature height is only 2 to 4 feet.
When selecting shrubs, it is important to consider the vicinity of streets or sidewalks so as not to invade their space. This sometimes happens with Cornus sericea (red twig dogwood). This shrub can reach 12 feet in width; and, when used in narrow sites, it must be pruned excessively, which is detrimental to its health and ornamental quality. Other shrubs, such as Pryacantha coccinea (Firethorn), grow as large as Cornus sericea and have spines, creating another landscape problem.
Check local ordinances before planting shrubs in parking strips as there may be restrictions
for those public areas.
Depending on the situation, some shrubs that may be suitable to a parking strip include Physocarpusopulifolius ‘Nana’ (dwarf common ninebark) or Lonicera xylosteum ‘Claveyi’ (Clavey’s dwarf honeysuckle). Many others exist as well.
Healthy soil allows roots to grow sufficiently so the shrub can obtain adequate amounts of water and nutrients. Urban and suburban soils frequently provide a challenge. They have often been modified by construction and grading practices and can be quite variable.
While Utah soils tend to be alkaline (high pH) and low in organic matter, soil conditions in individual locations may vary from one area to another. Prior to planting, it is a good idea to have soil tested for pH, salinity, texture, and nutrient levels. Utah State University provides soil testing services for a minimal charge. Contact your county USU Cooperative Extension office for details on how to submit a soil sample or see the “Soil Testing Guide for Home Gardeners” which gives detailed instructions.
A basic understanding of soil properties helps avoid possible problems associated
with improper plant selection.
Solutions to Soil Problems I: High Salinity (soluble salts)
Solutions to Soil Problems II: High pH (alkaline soil)
Solutions to Soil Problems III: Drainage
Solutions to Soil Problems IV: Soil Structure
Solutions to Soil Problems V: Low Organic Matter
Improper irrigation, especially overwatering, is a primary way that shrubs are killed or damaged within the first year of being planted. The soil around the rootzone of most shrubs and landscape plants should be allowed to dry out between irrigations. However, do not allow the soil to dry so much that new plants begin to wilt. Keep in mind that there is not an exact system to indicate how much to water at any given time.
Many variables, such as daily temperatures, natural precipitation, soil type and sun exposure, influence the need for watering. For example, conditions such as dry, hot weather and sandy soil would mean that shrubs should be watered more frequently. Conversely, cool weather and clay soil would mean that shrubs would need to be irrigated less frequently.
Other aspects of irrigation that can often negatively affect plant health include broken sprinkler heads and leaking pipes that can cause shrubs to receive inappropriate amounts of water, causing stress. Sprinkling systems should be checked regularly to avoid possible problems. Newly installed plants usually require more frequent irrigation for two years after being planted.
Another way to avoid improper watering is to use a principle called hydro-zoning.
This is a method of placing plants of similar water needs in the same irrigation zone.
The sprinkler controller can then be adjusted so that these plants receive an appropriate
amount of water. When this principle is used, landscape plant health is increased
and fewer plants die, thus reducing overall costs to homeowners.
Efficient Irrigation of Trees and Shrubs
Fluctuations and extremes in temperature are common in Utah. Before choosing a shrub
for any location, it is
important to know the average coldest temperature expected (hardiness zone) and choose plants accordingly. USDA hardiness zone maps are published online and in many gardening books.
Another useful reference is this USU Forestry fact sheet that shows USDA zones and other temperature information for several areas in Utah. Shrubs at the extremes of their hardiness range may need to be planted in protected areas, behind walls or windbreaks.
Most yards have landscape zones that vary from being mostly shaded to very sunny.
Intense sunlight can scorch
above-ground parts of sensitive species and cause leaf dehydration or even death. Even shrubs that normally tolerate full sun conditions may suffer if temperatures become excessively high or if they receive excessive reflected light from being planted on the south or west sides of structures.
Choose shrubs for their tolerance to sun or shade. Pay particular attention during the hottest part of the day. Winter sun can also be damaging to broadleaf evergreens and some needled evergreens such as Taxus (yews). Place these plants in areas where they will receive afternoon shade in all seasons. One thing to be especially cautious of is that plant description tags often list plants as needing full sun. In the Intermountain West, this does not hold true for some species, especially broadleaved evergreens.
Wind in Utah landscapes should always be considered. Non-native broadleaf evergreens such as Prunus laurocerasus (European cherry laurel or English laurel), Photinia x fraseri (red tip photinia) and Euonymus japonica (Japanese euonymus) are especially susceptible as leaves and buds dry out due to wind.
Drying winds during all times of the year can cause certain plants to not be able to draw enough water from the soil (even when the soil has a sufficient water supply), which eventually leads to drought symptoms (scorch within leaf margins and leaf drop). Wind tunnels can be created in urban areas wherein wind is channeled by buildings or other structures, which can also increase water stress to plants.
List of Landscape Shrubs
The list that follows contains many species commonly grown in Utah landscapes. However,
this does not mean
that they will grow in every landscape situation in Utah or that Utah State University officially endorses their use. Some are listed for their prevalence in Utah landscapes even though better adapted or less invasive shrubs potentially could be used in their place.
Common and botanical names
Both the common and botanical names are listed for ease of use. Whenever possible,
using the botanical name is
preferable, especially when dealing with those in the green industry, so that an exact plant can be correctly identified. In many situations, plants have common names that differ by region.
One example is Photinia x fraseri. In the southeastern United States, this species is frequently referred to as “red tip.” Locally, though, it is better known as “Fraser’s photinia” or simply photinia.
Some other examples include Hibiscus syriacus, known locally both as althea and rose of Sharon, and Potentilla fruticosa, referred to as both shrubby cinquefoil and potentilla.
Plant sizes listed are approximate. Environmental conditions often influence eventual size and how fast a plant will grow.
United States Department of Agriculture hardiness zones are used in this publication. However, they should not be the only factor used in determining if a specific plant will grow in a specific area. Other factors determining plant survival include micro-climates, soil type and sun exposure.
Water use requirements
Water use requirements are listed as very low, low, medium and high. Plants in the “very low” category will usually survive with no additional moisture than what they receive from natural precipitation. Shrubs listed in the “low” category will survive with deep watering as little as once a month during the growing season. Plants in the “medium” category need deep watering every two to four weeks. Plants in the “high” category need at least weekly irrigation during the growing season. These recommendations are for established plants. When plants are first installed, they usually need supplemental irrigation for up to 2 years.
Brenzel, K. 2005. Western Garden Book. Sunset Publishing Corporation. Menlo Park, CA.
Dirr, M. 1997. Dirr’s Hardy Trees and Shrubs. TimberPress. Portland, OR.
Dirr, M. 1998. Manual of Woody Landscape Plants. Stipes Publishing LLC. Champaign, IL.
Mee, M., Barnes, J., Kjelgren, R., Sutton, R., Cerny, T., and Johnson, C. 2003. Water Wise Native Plants
for the Intermountain West. Utah State University Press. Logan, UT.
Missouri Botanical Garden. 2009. Kemper Center Plant Finder. St. Louis, Missouri. 10 Jauary 2009.
Oregon State University. 2009. Oregon State University Landscape Plants: Images, Identification, Uses. Corvallis, OR. 10 Jan 2009.
United States Department of Agriculture. 2009. USDA Plant Database. Washington D.C. 10 January 2009.
University of Connecticut. 2009. Uconn Plant Database. Storrs, CT. 10 Jan 2009.
For a comprehensive list of Landscape Shrubs scroll to the end of this publication (p.4).
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