There are two ways to trim and edge turfgrass around sidewalks, flower beds, trees, buildings, etc. You can trim the turfgrass mechanically with a string trimmer and/or an edger, or you can use a non-selective herbicide such as glyphosate (Roundup® and similar chemicals). There are advantages and disadvantages to each method.

Mechanical Edging and Trimming
Using hand or power tools to trim and edge turfgrass gives a very sharp, neat edge; however, it is more labor-intensive than chemical edging. Many people trim or edge only once every two to four weeks, but, for optimum appearance, the trimming and edging should be done whenever the lawn is mowed – especially with aggressive Southern turfgrasses. This frequent trimming and edging is the normal practice for commercial lawn care operators. All of that trimming and edging is hard work and time consuming, whether done by a homeowner or a commercial lawn care service.

Chemical Edging
It is also possible to edge along turfgrass using a herbicide spray. This method is fast, easy and relatively inexpensive if the herbicide is bought in larger quantities from a farm supply store. If done carefully, it is possible to attain a neat, smooth edge. Chemical edging will usually last longer than mechanical edging and will not need to be repeated as often.

There are, however, several negatives to chemical edging. One negative is that a chemical like glyphosate generally takes seven to 10 days to kill the grass on which it is sprayed, so the results are not instantaneous as with mechanical edging. Even after the grass dies, it is still there – gradually decomposing over a period of weeks.
 
Drift is another potential problem with chemical edging. If there is any wind blowing and/or if you are not careful, the spray can drift beyond your target area (Figure 1). Perhaps the most insidious problem with chemical edging is that once you kill the turfgrass, something worse is likely to sprout up. There is no residual or preemergence effect with chemicals such as glyphosate.
 
When you kill off the turfgrass, coarse grassy weeds and ugly broadleaf weeds will probably germinate (Figure 2). Without the shade and competition from turf, weeds will sprout. The weeds will be ugly, but worse, the type of weeds that germinate will be less susceptible to herbicides such as glyphosate so subsequent sprays may not kill them. A further problem is a strong tendency for the person spraying to expand the sprayed area each time it is sprayed, thus a neat, narrow chemically edged band gradually becomes a wide, irregular, weedy swath (Figure 3).

Chemical Trimming Combined with Mulching
The place where chemical trimming excels is control of weeds in mulched beds or in mulched circles around trees. You can use a herbicide to kill off existing vegetation, then apply 2-4 inches of mulch. After that, you can usually control any weeds that break through the mulch with occasional touch-up sprays. Just be careful to resist the temptation to edge around the bed with each spray. If you do, you will kill the turfgrass off past the mulch and leave a bare area for weeds to germinate.

In summary, mechanical methods are generally superior for edging along turfgrass, but chemical methods can work well for some trimming tasks. You just need to use the right tool – mechanical or chemical – for each task.