Landscape - Weed Breaks in Landscape Beds

This is the time of the year that we see many weed breaks through mulch in landscape beds. The following is some information on this topic.

Common summer annual broadleaf weeds such as lambsquarters, pigweed, and morningglory may be found as weed breaks in landscape beds. Crabgrass is a common problem in landscape beds as seeds coming from nearby lawns can grow on the mulch surface. Perennial weeds such as nutsedge and mugwort can grow through the mulch. It is important to evaluate beds where weed problems are found for the underlying causes. Is mulch too thin or too thick? To be most effective, organic mulches such as bark should be applied at least 2 inches thick to block out the light and inhibit seed germination. However, too deep of mulch can create an environment where weed seeds can germinate and survive entirely in the mulch layer. Mulch needs to be able to dry out quickly and stay dry on the surface to limit germination of seed that is blown in or deposited on the mulch. Keeping mulch wet with irrigation can promote weed seed germination. Weed breaks often occur around new plants that were installed where soil was brought up to the surface along with weed seeds or where weeds came in with the nursery plants. Nutsedge and mugwort commonly are introduced with planting material. Inspect all nursery stock and reject those plants with perennial weed contamination.

To deal with weed breaks, there are a few postemergence products for broadleaf weeds including Sedgehammer (formerly Manage), Basagran, and Lontrel . Check the labels for specific uses and landscape plants that that are tolerant of these broadleaf materials. Acclaim, Fusilade, Ornamec, Vantage and Envoy are all available for grass control over the top of broadleaf ornamentals. Glyphosate products (Roundup, many others), Finale, and Scythe are used for non-selective control of weed breaks in landscape beds as directed, shielded, or wiper applications.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County