Shrub Functions

31 March 2008

Virginia Cooperative Extension, Charlottesville/Albemarle County Office
460 Stagecoach Road, Charlottesville, Virginia 22902
phone: 434.872.4580   fax: 434.872.4578

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What is a shrub? A shrub is generally considered a multi-stem woody plant that is less than 15 feet tall. Of course, this and other plant size categories are definitions contrived by humans to categorize nature. What is the difference between a large shrub and a small tree? In many cases, there is none. A shrub does not become a tree just because it grows higher than 15 feet. Classifying plants into ground cover, shrub, and tree designations are aids to allow us to conveniently classify and describe plants, albeit with a significant amount of ambiguity.

A root-bound shrub.

Shrubs are often placed at the base of a home to hide the foundation. Historically, early houses were built without deep footers, basements, or crawl spaces. Thus, the base of the house appeared unkempt and plants were used to cover the unsightly area. In some modern-day houses, the foundation is not covered by facade materials (e.g., brick, siding) as the rest of the house. Thus, foundation plants cover the non-facade areas. In some cases the facade covers the entire lower portion of the house. Regardless of the house construction, foundation plants are used to impart a solid feeling to the structure and visually link the house to the surrounding landscape. Foundation plants also break up the stark right angle junction of house and ground. Evergreen shrubs, either broadleaf shrubs (e.g., boxwood, rhododendron, Japanese holly) or conifers (e.g., junipers, dwarf pines) are used so that the structure is covered the entire year. You can select species so that you have some showy seasonal attractiveness in the planting such as flowers, brightly colored foliage, or red fruit. You must take into account the mature size and growth rate of the selected species to minimize the need for frequent pruning and other maintenance tasks (e.g., removing leaf litter, spraying). This is especially true for shrubs placed near windows and doors.

Adjacent houses, sections of landscapes, or private portions of a home landscape are often separated or enclosed by a shrub border, often called a hedge. There are many shrubs that can effectively serve as hedges. There are also several tree species such as hornbeams (Carpinus betulus and C. caroliniana), beeches (Fagus grandifolia and F. sylvatica), and hedge maple (Acer campestre) that can be pruned into hedges. Shrub borders generally are more aesthetically pleasing and less expensive than the cost of installing a fence. However, a shrub border usually requires more maintenance than a fence. You should consider the mature size and growth rate of the shrub species to minimize the need for frequent pruning and other maintenance tasks. Hedges do not necessarily need to be tall. The classic French and English parterre gardens have planting beds that are edged with tightly clipped low hedges. Hedges may be composed of evergreen or deciduous species.

Accent plants are those placed next to a prominent landscape feature to frame or add emphasis to that feature. Examples of accent plants are 1) shrubs placed on either side of a doorway or entry path, 2) a vine covering an arbor or espaliered around a doorway, and 3) shrubs placed to the side or beneath a sign, boulder, or sculpture.

In some cases, a woody plant will have significantly showy attributes that warrant featuring it as a specimen plant. Such a plant is usually strategically placed in the landscape where a view is focused, and hence becomes a focal point. Trees usually serve as specimen plants, but some very showy large shrubs such as crape myrtle, rhododendron, or dwarf conifers can have attributes which confer specimen plant status such as having more than one season of attractiveness, handsome foliage, interesting form, and showy bark. You can draw attention to a particularly handsome plant when other shrubs, usually similar in size, shape, color, or texture, are used to frame, surround, or serve as a background for the specimen plant.

As mentioned, shrubs can be grouped in a landscape to serve a dividing function. However, in the case of a mass planting, shrubs in an island bed serve more of a landscape statement than a screening function. As such, they add dimension and drama to the landscape. Mass plantings are used in large landscapes that can accommodate this use of shrubs.

Ground-cover shrubs are low-growing shrubs (around 3 feet or lower) and often have a spreading habit. Ground covers are commonly used to cover large portions of planting beds or landscapes. Relative to landscape design principles, ground covers and mass plantings serve the repetition principle in which plants of a particular size, shape, color, and texture are repeated to easily lead the eye through a landscape and connect portions of the landscape. Ground covers also reduce the amount of turf that has to be mowed, give the landscape a three-dimensional appeal, and serve as wildlife habitats. Examples of ground covers are shore, creeping, and Japanese garden juniper, pachysandra, and vinca. Ground covers, especially those that are low in stature and drought tolerant, are good candidates for areas with shallow, rocky soils.

Most shrubs are sold as container-grown plants and a small percent of shrubs are sold as ball and burlap (B&B) plants. When purchasing a container-grown plant, make sure that the plant is not root-bound (a condition when the plant has stayed in the container too long and the soil ball is composed of a solid mass of roots that often encircle the root-ball. You can plant a container-grown plant most of the year but the best time to plant is in the spring and fall.

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For more information about this and other landscape topics contact your local Virginia Cooperative Extension office. The local Virginia Cooperative Extension office numbers are Albemarle 872-4580, Fluvanna 591-1950, Greene 985-5236, Louisa 540-967-3422, and Nelson 263-4035.