What Does a String Trimmer Do? | Beyond the Lawn Mower’s Reach

Every lawn has them: the awkward strip between the sidewalk and the curb, the tufts hugging the fence post, the grass creeping up around the mailbox. A mower either can’t fit or risks nicking the obstacle. A string trimmer handles these edges and tight corners by spinning a monofilament nylon line at high speed, slicing through grass and light weeds on contact. It is the finishing tool that makes a mowed yard look professionally edged.

The Core Job: Trimming Where a Mower Can’t Go

A string trimmer is a handheld tool built for precision cleanup. Instead of a rigid metal blade, it uses a flexible piece of line that whips around fast enough to cut vegetation. This design lets you work right up against hard surfaces—fence lines, tree trunks, walkways, and foundation walls—without damaging the trimmer or the obstacle itself.

The typical layout is a long shaft with a rotating head at the bottom and a gas engine or electric motor near the top or base. You guide the head with a sweeping motion, letting the line do the cutting. It excels at three jobs:

• Edging: creating a clean border between your lawn and sidewalks, driveways, or garden beds.
• Cleanup: clipping grass and weeds around obstacles like fence posts, trees, and utility boxes.
• Tough spots: reaching into tight corners, along steep slopes, and under bushes where a mower deck won’t fit.

The line wears down with use, and most trimmers have a way to feed out more—either by tapping the head on the ground or by manually advancing it.

String Trimmer vs. Edger: What’s the Difference?

A string trimmer is the more versatile tool of the two. It can both trim and edge, making it the better first purchase for most homeowners. A dedicated edger, however, is a specialized machine designed for one task: cutting a crisp, defined groove between the lawn and a hard surface like a sidewalk.

Edgers typically use a rigid metal blade spinning perpendicular to the ground, which cuts a deeper, cleaner line than a trimmer can. If you are particular about having a sharp, trench-like border along your driveway, an edger does it better. But for all-around yard maintenance, a string trimmer covers more ground.

Battery, Gas, or Corded: Pick the Power Source

Your choice of power source shapes how and where you can use the trimmer. Consumer Reports’ string trimmer buying guide breaks down the trade-offs among the main types.

• Corded electric: Lightweight, instant start, and unlimited runtime, but limited by the length of your extension cord. Best for small to mid-sized yards close to an outlet. If you want a top pick for this type, our roundup of the best corded electric string trimmers covers tested models.
• Battery-powered: Cord-free convenience with no gas or pull-start hassle. Runtime is limited by battery charge, so consider a spare battery for larger lawns.
• Gas-powered: Maximum power and runtime, ideal for large properties and thick growth. Heavier, noisier, and requires more maintenance like fuel mixing and air filter cleaning.

Match the power source to the size of your property and your tolerance for maintenance.

Using a Trimmer Safely

A string trimmer spins fast enough to fling debris like small stones and bits of grass at high velocity. Safety guidance from the North Carolina Department of Transportation’s workplace procedures for string trimmers and brush cutters stresses eye protection as non-negotiable. Wear safety glasses with a face shield or screen, along with gloves and hearing protection, whenever you start and operate the tool.

Dress for the job in long pants and sturdy shoes, and check the area for rocks, wire, or other debris before you begin. Also know the tool’s limits. A string trimmer handles grass and light brush well, but pushing it into dense, woody growth overworks the machine and risks damaging it—heavy brush calls for a dedicated brush cutter or a trimmer with a blade attachment.