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 Home>Lawn & Garden>Home Gardening>Lawns>

Mechanical vs Chemical Trimming

You can trim and edge mechanically with a string trimmer or edger or chemically with a non-selective herbicide. Dr. Dick Parish, an engineer at the LSU AgCenter’s Hammond Research Station, says each method has advantages and disadvantages.

Using hand or power tools to trim and edge turfgrass mechanically gives a very sharp, neat edge; however, it’s more labor intensive than chemical edging.

Many people trim or edge only once every two to four weeks. But for optimum appearance, Parish says trimming and edging should be done whenever you mow your lawn – especially with aggressive Southern turfgrasses.

"Although frequent trimming and edging is the normal practice for commercial lawn care operators, it’s hard, time-consuming work, no matter who does it," Parish says.

Parish says it’s also possible to edge grass by spraying a herbicide. This method is fast, easy and relatively inexpensive if you buy the herbicide in larger quantities from a farm supply store or similar outlet.

If done carefully, you can get a neat, smooth edge. Chemical edging will usually last longer than mechanical edging, so it won’t need to be repeated as often.

Parish warns, however, that chemical edging has several drawbacks. One is that some chemicals may take seven to 10 days to kill the grass, so the results are not instantaneous as with mechanical edging. And even after the grass dies, it’s still there – gradually decomposing over a period of weeks.

Drift is another potential problem with chemicals, Parish says. If any wind is blowing or if you’re not very careful, the spray can drift beyond your target area.

"Perhaps the most insidious problem with chemical edging is that once you kill the turfgrass, something worse is likely to sprout up," Parish says.

Many non-selective herbicides have no residual or preemergence effect.

"When you kill off the grass, coarse grassy weeds and ugly broadleaf weeds will probably germinate," Parish says. "Without the shade and competition from turf, weeds will sprout."

The weeds will be ugly. But worse, the type of weeds that germinate may be less susceptible to herbicides so subsequent sprays may not kill them, he says.

A further problem is a strong tendency for the person spraying to expand the sprayed area each time it’s sprayed.

"A neat, narrow chemically edged band gradually becomes a wide, irregular, weedy swath," the engineer says.

Chemical trimming works best to control weeds in mulched beds or in mulched circles around trees, Parish says.

"You can use a herbicide to kill off existing vegetation, and then apply 2 to 4 inches of mulch," he says. "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," he cautions. "If you do, you’ll kill the turfgrass past the mulch and leave a bare area for weeds to grow."

Parish says mechanical methods are generally superior for edging along grass, while chemical methods can work very well for some trimming tasks.

"You just need to use the right tool – mechanical or chemical – for each task," he says.

For information on more Lawn & Garden topics, contact an extension agent in your parish LSU AgCenter office. In addition, please see the Get It Growing section of the LSU AgCenter Web site.

Last Updated: 12/1/2014 3:41:44 PM
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