Weed eaters, also known as line trimmers and weed whackers, are well suited for edging flower beds, as long as you observe a few precautions. One is to avoid using a model that's too powerful for the job, or you can end up scalping the edge instead of trimming it. Battery-powered and plug-in models are usually your best bet for lawn trimming. The other precaution is to wear protective clothing, including shoes and glasses. Flower bed edges are full of small rocks, twigs and other potential projectiles, and weed eaters -- even small ones -- are deceptively powerful machines.
Clear debris from the edges of the flower beds so the weed whacker doesn't do it for you. Beside shooting out in unpredictable directions, leaves, twigs and rocks will prematurely shorten the trimmer string.
Plug in the machine or, if it is a battery-powered model, insert a fresh battery. If you're using a gas-powered model, turn on the choke, pull the starting cord and turn off the choke as soon as the engine starts running.
Position the handle in a comfortable position on the shaft and tighten the nut to secure it. Support the trimmer by holding the handle with one hand while you operate the trigger with the other hand.
Tap the trimmer head against the ground to advance the string it before you start edging. The weed whacker will automatically trim the string to its optimal length when you begin.
Hold the trimmer at waist height with the string head over the edge of the garden. You should be standing on the grass, not in the garden. Pull the trigger and lower the head at an angle of about 60 degrees with respect to the ground while you let the ends of the strings do the cutting.
Sweep the trimmer head back and forth while you gradually reduce the angle of the head to bevel the edge of the lawn. Move around the perimeter of the bed, using the same motion, until you return to your starting point.
Turn the trimmer off, and unplug it or remove the battery when you're finished.