Landscaper corner
Weed Management Strategies for Ornamental Landscape Beds and Ground Covers By James McCurdy, Ph.D., Assistant Professor, Mississippi State University
W
eed control in ornamental landscapes is challenging. The diversity of plant material within these systems and the types of weeds that occur are much different than those in dense monoculture turfgrass. The use of mulches and frequent soil disturbance further compounds the complexity of weed control. Just like in turf systems, cultural practices are the most important underlying reason for a successful, weed-free landscape. But unlike maintained lawns, ornamental landscapes require a larger degree of planning and preparation in order to maximize their success.
Design and preparation
The most crucial step in ornamental bed preparation is planning prior to construction. Planning plant material and making sure that the soil and site characteristics accommodate those plants are fundamental to successful landscapes. For instance, not all plants necessitate soil renovation; many can 10 • Mississippi Turfgrass • Spring 2017
readily handle wet, poorly drained soils or, alternatively, dry and un-irrigated conditions. Weed suppression depends upon healthy plants that compete with weeds for resources, such as nutrients, sunlight and water. Water management is an important part of successful landscapes. An important function of any landscape is to mitigate stormwater runoff. The key to this function is that water infiltrates slowly through the natural soil rather than being forced to run off quickly into sewers and streams. Too often, however, landscape designers treat ornamental beds as water confluence features where water is meant to flow and channel rather than slowly infiltrate. This mistake leads to increased disturbance of mulch and havens for weeds. Creative hardscapes can help ease these issues and also facilitate non-selective weed-control options (Photo 1). These hardscapes are semi-pervious and accommodate excess runoff without soil erosion.
Dense plant canopies and year-round cover provide more weed suppression than even the best herbicide program. Achieving this density often requires multi-tiered plantings of upper canopy plants supported by underlying ground covers. Ground covers not only suppress weed growth, but they also enable easy preemergence herbicide selection, as they are usually perennials (Photo 2).
Mulch is part of the solution and part of the problem
Mulch quality and thickness are critical to successful ornamental landscapes. Mulch is meant to cover the weed-seed bank and prevent seedling establishment. If the mulch is too thick, however, it compromises preemergence herbicide control — these herbicides become bound to organic matter rather than penetrating to the site of seedling germination. If mulch is too thin, weed seeds emerge with ease. Mulch is rarely weed free. When