Summary
- Weeds may be controlled in landscape beds without using herbicides.
- Perennial weeds such as bermudagrass and nutsedge should be controlled before landscape beds are established.
- Solarization, geotextiles, and organic mulch effectively control most annual and some perennial weeds.
- Several devices are being sold to control weeds without the use of herbicides, such as flamers, hot water steamers, and robotic weeders.
- These may be effective on small annual weeds but usually do not control perennial weeds.
Yellow nutsedge (Cyperus esculentus) is an invasive weed that is difficult to control in a landscape bed.
Ted Whitwell, ©2023, Clemson Extension
Weed Problems
Major weed problems associated with landscapes include many of the same species found in turf areas, plus woody perennial vines and tree seedlings that are very difficult to control. Greenbriar, honeysuckle, wisteria, and seedling trees often sprout and become established, making it difficult to remove by hand weeding. These types of weeds have deep roots in the mulch and are not easily controlled by herbicides.
Annual weed seeds and perennial vegetative parts are often introduced into landscape beds by mowing, weedy mulch, or topsoil. Mulch from municipalities often consists of ground-up yard waste, usually containing weed seed, tree seed, and vegetative parts of weeds. This type of mulch should only be used where beds can be surveyed frequently to avoid introducing new weed problems.
Weedy topsoil will introduce weed problems into the landscape.
Weedy topsoil will introduce weed problems into the landscape.
Weedy species may indicate soil or environmental problems in the landscape, such as low soil fertility, soil compaction, high or low soil water availability, poor drainage, and high or low soil pH. The challenges of developing and implementing an effective landscape weed management program include accommodating a wide diversity of landscape plant species and sites, growth habits, and growth rates.
After the landscape installation and during the first years after planting, annual weeds are normally the most common problem. Tillage, cultivation, and mowing are not routinely practiced in landscape beds, which allows for the development of invasive woody species, such as green briar, tree seedlings, wisteria, and turf species.
The type of plant material in the landscape largely determines the availability of weed management options. Landscaped areas should be surveyed in the spring to determine weed problems before developing the beds. Existing annual and perennial weeds should be controlled during the summer before installing the landscape plants in the fall or spring. Soil samples should be taken several months before planting.
Hand Removal: When hand removed from landscape beds, weeds should not be allowed to remain near the site. Some weeds could complete seed development after being removed from the soil, and the seeds may germinate and continue to be a problem. Common weed seed sources come from contaminated topsoil, mulch, and equipment.
Solarization: This is when the soil is heated by using plastic sheets to retain radiation from the sun to kill soil-borne pathogens, weed seedlings, and some underground perennial plant parts. Soil should be tilled and irrigated prior to applying the clear plastic cover. The plastic cover should remain on the bed area for 4 to six weeks to allow the soil temps to reach sufficient levels to control the pests. Summer is the preferred time to solarize beds. The ends of the plastic cover should be covered with soil to keep the plastic in place. This method works well before desirable plants are installed.
Tillage: Tilling the soil when establishing landscape beds is another method that can be used to control perennial weeds. It should be timed to bring perennial root systems to the soil surface during adverse growing conditions, such as drought or cold temperatures.
Landscape irrigation practices often promote weed emergence and establishment by too little or too much water. Landscape beds should be well-drained to prevent standing water from developing saturated soils. Poorly drained soils will foster weed emergence and growth and inhibit the growth of desirable plants.
Geotextiles (Weed barriers): Geotextiles are usually placed on the prepared beds, and the landscape plants are planted through the porous fabric with mulch placed on top. The advantage of geotextiles over plastics is that they permit the exchange of water and air between the soil (roots) and the atmosphere. However, geotextiles do not completely control all the weeds. Weed growth may become a problem in the mulch when geotextiles are topped with mulch. Mulch shifting and exposure of the geotextiles also can be a problem. Geotextile fabrics are not very useful in annual flower beds because of the frequent replanting, but they may be beneficial in some perennial beds.
The ends of the plastic should be covered with soil so the wind will not remove it.
Ted Whitwell, ©2023, Clemson Extension
Poorly drained soils will foster weed emergence and growth and inhibit the growth of desirable plants.
Ted Whitwell, ©2023, Clemson Extension
Unsightly plastic in landscape beds will prevent the proper exchange of water and air.
Ted Whitwell, ©2023, Clemson Extension
Mulch: When using organic mulches, such as ground bark or pine straw, a 2- to 4-inch layer will help prevent weed emergence and growth. The depth of the mulch will depend on the particle size of the mulch, mulch type, and weed pressure. Organic mulches also reduce and buffer soil temperature, decreasing the maximum temperatures at the soil surface.
Mechanical Control: Several devices are being sold to control weeds without the use of herbicides. These include flamers, electrocution devices, ultraviolet light, robotic tillage devices, and hot water steamers. Most of these will control small annual weeds, but care must be taken not to damage landscape plants or the operator.
This is an excellent example of an annual flower bed with good weed control.
Ted Whitwell, ©2023, Clemson Extension
References:
- Horticultural Research Institute – www.hri.org
- Leslie, A. R. (Editor). 1994. Handbook of Integrated Pest Management for Turf and Ornamentals. CRC Press, Boca Raton, FL.
- Price, R. P. 1986. Nursery and Landscape Weed Control Manual, Thompson Publications, Fresno, CA.
