How to Use a String Trimmer Correctly? | Safety Rules That Matter

Guide

Run a string trimmer only with its approved cutting head, line, and deflector fitted, full protective gear on, and bystanders at least 50 feet away.

A string trimmer throws small debris at high speed — a pebble off the head can crack a lens or break skin, and that’s the failure most people don’t see coming. The working method is less about technique and more about the five-minute setup and inspection that comes before the trigger is ever pulled. Get the machine configured correctly and the cutting part takes care of itself.

Everything below follows STIHL’s published safety and owner’s manuals, the same documents the equipment ships with. Confirm the details against your own model’s manual, since heads, line sizes, and starting sequences differ from one trimmer to the next.

What Should You Check Before Starting a String Trimmer?

Inspect the machine before every single use, and never operate it with a damaged or missing deflector. That guard is the part that stops debris from reaching your body, and it is not optional.

Walk through these items while the tool is off and the battery is out or the fuel cap is tight:

  • Throttle trigger and trigger lockout — both should move freely and return on their own.
  • Stop switch — confirm it kills the motor.
  • Cutting attachment and deflector — check for cracks, wear, and correct fit.
  • Line — the right diameter for your head, with no wire or metal-reinforced line (the FSA 120.0 manual prohibits both, along with circular saw blades on that model).
  • Harness, fasteners, and battery or fuel system.

Line specs matter more than people assume. Oversized line strains the motor; the wrong guard combination exposes more of the spinning head.

Next, walk the work area. Pull stones, glass, wire, and toys out of the path — anything the head can fling. Then keep children, pets, and helpers at least 50 feet back, the distance the STIHL Trimmer and Brushcutter Safety Manual specifies.

Protective Gear Standard or Detail Why It Matters
Eye protection Glasses or goggles rated ANSI Z87.1 Stops flung stones and clipped line
Hearing protection Earplugs or muffs Gas models run loud for long stretches
Leg and foot cover Long pants, sturdy closed-toe boots Deflects debris thrown low and back
Face shield Optional add-on over eye protection Extra barrier when clearing brush
Gloves Close-fitting work gloves Grip and vibration comfort
Bystander distance At least 50 feet (15 m) Outside the debris throw zone

How Do You Start and Hold a Trimmer Safely?

Start the trimmer outdoors on firm, open ground, and for a gas model begin at least 10 feet (3 m) from where you fueled it.

Battery models need the unit switched off before the battery goes in, and you should never carry a running trimmer with a finger resting on the trigger. The FSA 120.0, FSA 120.0 R, FSA 80.0 R, and FSA 200 R manuals all bar use in rain, damp, or wet conditions, and they require battery removal during breaks and storage.

Once it’s running, set your stance before you cut. Both hands on the controls where your manual requires it, feet planted, no overreaching. Hold the head near ground level and roughly parallel to the ground, then sweep side to side in slow, even passes. Let the tip of the line do the cutting instead of forcing the head into the grass.

Keep the head off fences, rocks, and tree trunks. Tilting the head perpendicular to the ground exposes more of the spinning attachment and cuts your control. If you’re shopping for a machine built for heavier growth, this roundup of tested professional string trimmers covers models rated for sustained work.

What Should You Do Before Clearing a Jam or Changing Line?

Stop the motor and, on a battery model, pull the battery before you touch the head. Clearing wrapped grass, swapping line, inspecting for damage, taking a break, or setting the tool down all require a dead machine first.

On a gas trimmer, wait until the attachment stops completely before you reach anywhere near it. A head that’s coasting still cuts. Once it’s still, clear the wrapped material by hand — never with the tool running — and check the line length against your attachment’s spec when you refill.

The mistakes that cause most injuries are consistent: running without the deflector, fitting wire or an unapproved blade, loading line thicker than the head allows, cutting in wet weather or after dark, and carrying a live trimmer with a finger on the trigger. One more that surprises people — a string trimmer is not a hedge trimmer, and the safety manual says so outright. Use the right tool for the cut.

Controls, line diameter, deflector, harness, and approved attachments vary by model, so read your exact owner’s manual before the first start. Improper use can cause serious or fatal injury, and the manual is where your machine’s real limits live. STIHL’s trimmer and brushcutter safety manual spells out the full operating rules.

Common Questions

Can I use any brand of line in my trimmer?

Use line that matches your attachment’s specified diameter and type, and avoid wire or metal-reinforced line unless your manual explicitly allows it. Mismatched line can strain the motor or feed poorly.

Is it safe to trim wet grass?

No — battery trimmer manuals prohibit use in rain, damp, or wet locations. Wet conditions raise the risk of slipping, reduce your footing and visibility, and put moisture near electrical components on battery models. Wait for dry conditions and cut when you can see the ground and the head clearly.

How far should other people stay while I trim?

The STIHL Trimmer and Brushcutter Safety Manual puts the minimum at 50 feet (15 m). That distance keeps children, pets, and helpers outside the zone where the spinning head can throw stones, glass, or clipped line. Clear the area of loose objects before you start, too.

Sources