Managing weeds in the landscape can be accomplished by using a range of tools, management practices and chemical control options as part of an integrated pest management (IPM) program. Using a string trimmer is one of the more common practices used to address weeds in landscape settings. While the trademarked name Weed Eater has become the commonplace reference for the tool, it is also known as a string trimmer or weed whacker. These tools provide more precision in cutting vegetation in tight areas where mowers cannot fit, managing weeds around sensitive areas and features, or as a first step in recovering an overgrown area. Mowers are used for the vast majority of a lawn; however, the edges of the lawn are commonly manicured using string trimmers, particularly along fence lines, slopes and difficult-to-drive areas. Narrow, grassy locations, such as parking lot islands, may be difficult to drive over, rendering trimming a more effective management practice. Utility boxes and cleanouts, light poles, mailboxes and other outdoor features are commonly managed using string trimmers under or around the object as well. While trimming provides ease and accessibility for maintaining parts of the landscape, caution must be exercised to ensure desirable plants are protected and undesirable weeds do not proliferate. Bearing that in mind, consider the following options for tools, management practices and what weeds are present on-site.

Trimmer Options

Power source: Options abound when selecting what string trimmer works best for a site, situation or user. A variety of power options are available, including various gas-powered and electric-powered engines. In general, gas-powered engines provide more power, which may be necessary to address extremely overgrown areas. They also are heavier and more commonly used in commercial applications as they do not need to be recharged and are simply refueled. Pay attention to what type of gas engine you have. A two-stroke engine will require a gasoline-oil mix for fuel, whereas a four-stroke engine utilizes just gasoline. Electric-powered trimmers are often lighter and more convenient for nonprofessional users; however, the need to recharge can create limitations when maintaining large or multiple sites. While electric engines may sacrifice some power, general residential lawn care can be accomplished quite easily with electric string trimmers. Electric-powered trimmers are generally quieter than their gas counterparts, which can be of benefit when maintaining residential sites or working early or late in the day. Furthermore, electric trimmers may be easier for novices to start as they do not have rip cords and instead usually just have a switch. Advancements in electric tool technology may continue to close the gaps between the two technologies.

String vs. blade: The cutting tool of a trimmer is commonly a nylon string, hence the name string trimmer. The nylon string is thin — typically 0.065-0.095 inches in diameter — and may be individually affixed to the trimmer head (attaching two or more small sections into the head) or the entire spool may be placed within the head, allowing easy extension of the string as it breaks off. The soft nature of the nylon strings, as compared to larger plastic or metal blades, makes this material easier to use in sensitive areas, such as around fences or utility boxes, where the risk of scarring the object is reduced. Nylon string longevity may depend on material type (i.e., homeowner or contractor grade), level of use and operator practices. For thicker, dense vegetation, it may be useful to use more durable materials such solid plastic or metal blades. These blades are thicker (0.5-1 inch) and better suited for heavy-duty trimming. However, their durability may pose an issue with regards to damaging desirable features, such as hardscapes or fences, and their economic efficiency in that it’s cheap and easy to replace nylon strings.

Bearing these things in mind, select the right trimmer engine and cutting implement to fit your needs.

Management Around Ornamental Plants

Trimming around ornamental plants can cause more harm than help, particularly if the cutting mechanisms or strings get too close to tree trunks, shrubs or herbaceous plant material. Tree trunks may be injured by trimmer, where damage to the cambium layer — the ring just inside of the bark where the plant vascular system (xylem and phloem) is — can disrupt the flow of water and nutrients throughout the plant. Commonly, this damage leads to suckering where woody plants initiate new shoots as a stress response to injury. Shrubs, particularly those with low-growing foliage, may be visibly damaged but recoverable, whereas herbaceous plant materials can be permanently damaged or killed if impacted by trimmers. In all cases, trimming too close to ornamental plant materials should be avoided. Using smaller, more precise tools to perform close-quarter cuts provides one alternative; however, cultural practices such as mulching may provide longer-lasting, more sustainable weed management around trees. Taking a defensive approach to protecting trees can be accomplished by installing a plastic tree guard around the trunk. While the tree guard offers some protection from trimmer damage, caution must still be exercised when working around trees. When trimming near sensitive plants, slowly move the cutting tool from the outside in, allowing the cutting action to creep closer to the weed without overextending into the plant. (Image 1).

Safety and Suggestions

Always wear appropriate personal protective equipment when using a trimmer. Eye protection can prevent thrown objects, such as gravel, from harming yourself or others. Long pants and sleeves can help prevent yard debris or abrasive objects from causing harm to exposed skin. Be cognizant of pedestrians, windows and vehicles in the immediate vicinity of where you are working. Be mindful of irrigation lines, wires or other sensitive objects nearby. It is best to avoid trimming in difficult locations where people, trees, utilities or objects may be at risk (Image 2). Instead, use more precise tools, such as hand trimmers or hand removal, or herbicides to address weed issues in difficult to manage locations.

Weeds to Avoid

Using a trimmer is not an effective management practice for all weed species. Some weed species can spread by fragmentation, in which a fragment of the weed can root and grow into a full weed itself. Examples of common weeds which spread by fragmentation in Louisiana include alligatorweed (Alternanthera philoxeroides; Image 3), Virginia buttonweed (Diodia virginiana) and common purslane (Portulaca oleracea). Using a trimmer on these weeds can actually result in their spread by breaking the weeds into pieces and spreading them around the area and is not recommended. For management of these weeds, chemical control and hand removal are more reliable options. Grass and sedge weeds may not be effectively controlled by trimming alone and can often tolerate mowing/trimming. Trimming of these species may result in short-term control, but regrowth is likely. Hand weeding or herbicides may be a more effective long-term option for control of grass and sedge weeds in landscape plantings. Identification of weeds is critical to ensure that a management strategy will be appropriate and effective on the species present.

Another case in which using a string trimmer can be detrimental is with weeds that have produced seed. If weeds are allowed to mature and reproduce then trimming can actually spread the seed in the vicinity, resulting in a more severe infestation in future seasons. Remove weeds before they mature and reproduce. Weed management strategies are usually most effective when weeds are small. If weeds have produced seed, a useful strategy can be to place a bag over the reproductive parts of the plants and then remove the plants by hand. Preventing weed seed from entering the seedbank is a crucial component of weed management and will save money and effort in the future.

Image 1. Cutting a dogfennel weed by working from the outside in to avoid damaging desirable plants. Photo by Colton Blankenship

Image 2. Avoid using a string trimmer near tree trunks, irrigation lines or loose gravel. Photo by Colton Blankenship

Image 3. An alligatorweed stem fragment has begun rooting at the nodes. Photo by Colton Blankenship

For more information on trimming practices, please contact your local LSU AgCenter Extension office or visit www.LSUAgCenter.com

Authors

Damon E. Abdi, Assistant Professor and Extension Specialist, Hammond Research Station

Colton D. Blankenship, Assistant Professor and Extension Specialist, Hammond Research Station

P4009

8/22/2025

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