Mixed Screens

In the landscape, trees and shrubs are often used to create buffers and screens. On occasion, both may be used to frame a desirable view as well. Many plant species used are reliable performers, while others tend to lose popularity as they become unreliable in the landscape due to insect, disease, or cultural problems. The demand for the supply of new plantings perpetuates a constant ebb and flow in the horticultural market.

Leyland Cypress is an example of a plant commonly used as an evergreen screen planting for its uniformity and ability to provide a buffer for privacy, noise control, and as a windbreak. The Leyland Cypress planting model generally consists of using a single type of plant (termed monoculture) where plantings are oriented in one row with close and even spacing.

Leyland Cypress planted as a monoculture screen along a roadway.
LayLa Burgess, © 2017 HGIC, Clemson Extension

Leyland cypress trees are experiencing severe decline in many landscapes. Trees are being lost one by one, or several at a time in more severe cases because of disease or damaging pests in the monoculture planting system. When the choice of plantings are all the same, disease or insects that cause damage can be easily transferred laterally from plant to plant. However, many other potential factors contribute to plant health and decline such as drought and proper planting technique.

When individual plants in a screen die, it can be difficult to match the lost plant to the existing plantings. It should be possible to locate the same plant species or cultivar, but the once uniform and mature screen becomes dotted with smaller plants. This gives the appearance of being less manicured, less uniform, and may no longer function as an efficient screen. In essence, the once uniform screen is not so uniform anymore. One way to avoid this situation is to plant a mixed screen.

Multiple plant species in a mixed screen provide diversity and safeguard against potential insect and disease problems.
LayLa Burgess, © 2017 HGIC, Clemson Extension

A mixed screen moves away from the straight lined, monoculture design and instead uses groupings and layering of different types of plants. Mixed screens still provide all the functional aspects of privacy, noise control, and protection from prevailing winds, but in addition provide biodiversity to the landscape resulting in a number of benefits to plant health and longevity.

Planning for a Mixed Screen Design

Effect: There are different ways to achieve a mixed screen. Plants can be layered, staggered, placed in groupings (sometimes referred to as clusters), or combinations of these methods to achieve the desired effect. A series of layered plantings generally has the tallest plants located towards the back of the site with progressively smaller layers of plantings in the foreground, though there is some room for variation as in Diagram 1.

The staggered effect is achieved by placing trees and shrubs in 2-3 successive rows that are offset from one another. Offsetting the rows from each other fills in the gaps between the plants as in Diagram 2.

Clusters of plantings generally consist of installations planted in odd numbered groups of 3, 5, 7 or higher. The grouping maybe situated to block a view, create a noise barrier, or redirect prevailing winds in a particular location as in Diagram 3.

Evergreen vs. Deciduous: Evergreen plants keep their foliage throughout the year, while deciduous plants lose their leaves in the fall and flush out new growth in the spring. When trying to achieve a cohesive screen planting, most often the goal is to block an undesirable element in the landscape. Such elements may include prevailing winds, an undesirable view, excessive noise, intense lighting, or roadway traffic. Depending on the offending element to be screened, evergreen plants may be needed to provide year-round coverage. In this case, the majority of the screen composition can be evergreen, but deciduous trees and shrubs can be intermingled to provide interest as well as biodiversity. When choosing deciduous trees and shrubs, pay attention to the branch form and structure. This will provide winter interest during periods of limited to no foliage. Choose plants that clearly look different in plant form, foliar texture, flowering, or foliage color to enhance the interest of the screen at a distance.

Plant Selection: Tables 1, 2, and 3 provide a selection of evergreen plants commonly used in mixed screen designs for South Carolina. Choose a minimum of 2 types of evergreen conifers, 2 types of broadleaf evergreens, or 2 types of evergreen shrubs for diversity in the landscape.

Table 1. Evergreen Conifers

Table 2. Broadleaf Evergreens

Table 3. Evergreen Shrubs

Spacing: Regardless of the arrangement of plants in the mixed screen, plant spacing should adhere to individual plant size (i.e. height and width) at maturity. Avoid the temptation to install plants too close together to quickly achieve the desired effect. Plants not given adequate space, will eventually outgrow an area leading to crowding or excessive shading. Proper plant spacing provides good air circulation among plantings and lowers the chances of creating an environment that encourages plant disease or other complications such as, root competition for water and nutrients. Denote proximity to roads, sidewalks, driveways, utility lines, or drainage areas in order to avert potential future problems. For more information on planting trees and shrubs, refer to HGIC 1001, Planting Trees Correctly and HGIC 1052, Planting Shrubs Correctly.

Additional Features: Single specimen plants can be strategically placed to provide focal points throughout the mixed screen. Fences made of block, stone, brick, or wood intermingled within or adjacent to the screen can add interest or fill in space while plant materials mature. The placement of sculptures, birdbaths, birdfeeders, or benches can create an inviting feel to the space. However, keep in mind, less is often more.

Precautions: Once the mixed screen layout is determined and plant selections are considered, it is always a good rule of thumb to get a soil test prior to plant purchase. Soil test results provide information on soil pH adjustment, soil amendment recommendations, and fertilization needs. For more information, see HGIC 1652, Soil Testing.

Another important factor to consider is the availability of a consistent source of irrigation. New plantings require adequate water during the establishment phase. Once trees and shrubs become established, they need approximately an inch of water per week to survive and thrive. If installed properly, a drip irrigation system provides consistent irrigation. Irrigation systems may need to be adjusted as the plants grow larger or in times of higher water demand when temperatures increase. Make sure the emitters are not clogged and are working properly by checking the irrigation system periodically. Ground level irrigation encourages good water penetration into the soil at the root zone promoting proper plant health and successful mixed screens. A light layer of mulch will help the plants retain moisture and suppress weeds that often become competitors for nutrients. For more information on irrigation, refer to HGIC 1056, Watering Shrubs & Trees.

Originally published 08/17