To edge a lawn with a string trimmer, flip the tool so the head is vertical at a 90° angle, keep the deflector shield facing you, and walk opposite the line’s spin to toss debris onto the lawn.
Most people use a string trimmer for grass along fences, but with one change in orientation it can produce a crisp edge along sidewalks and driveways. The key is flipping the cutting head from horizontal to vertical and moving in the correct direction. Below is the exact method and common mistakes.
How to Position the Trimmer for Edging
Set the cutting head at a strict 90° vertical angle so the tip of the string slices through the grass-soil interface. If your trimmer has a rotating head mechanism, twist it upright. If not, manually rotate the shaft until vertical. With the head vertical, the deflector shield should face your body to direct debris onto the lawn. Flip your grip: hold so the trigger is accessible by thumb, gripping the side of the shaft for steadier control.
Which Direction Should You Walk?
Move opposite the rotation of the trimmer line. Most trimmers spin clockwise, so edge from left to right. This pushes soil and clippings onto the lawn rather than into the fresh cut. If your trimmer spins counterclockwise, edge from right to left. Walking the wrong direction forces debris into the cut path, creating a messy result.
Technique for a Clean, Even Edge
Start the motor to full speed before the line touches the ground. Use only the last inch of the string to slice vertically where grass meets the sidewalk, driveway, or flower bed. Lower the head until the line grazes the surface; pushing deep digs trenches and scalps grass. Look ahead at where you are walking rather than staring at the cutting head, which causes a wavy edge. Maintain a steady, brisk pace with relaxed arms. For tall or dense grass, take small bites and overlap passes.
Preparation Steps That Prevent Problems
- Mow the lawn first to set grass height and define the edge line. Edging over tall, uncut grass can scalp areas and create bare patches.
- Check the trimmer line before starting. It should extend 3 to 4 inches from the head and not be frayed, knotted, or brittle.
- Clear rocks, toys, hoses, and branches from the edging path. Spinning string can fling these as dangerous projectiles.
- Wear long pants, closed-toed shoes, and safety goggles. Keep pets and bystanders at least 50 feet from the operating area.
This technique works on gas, corded electric, and cordless battery string trimmers. See our tested recommendations for best grass edge trimmers with rotating head functionality.
| Common Mistake | Result | Fix |
|---|---|---|
| Angle not 90° vertical | Uneven cut or digging into soil | Check head position; line must move up and down, not side to side |
| Walking same direction as spin | Debris pushed into cut path | Edge left to right (clockwise trimmer) or right to left (counterclockwise) |
| Pushing head deep into soil | Messy trench and scalped grass | Use only tip of string; lower lightly until it grazes surface |
| Looking at head while walking | Crooked, wavy edge line | Look ahead at your path; maintain steady pace |
| Edging wet soil after rain | Deep ruts and muddy edge | Wait one day for soil to firm up |
Post-Edge Cleanup and Storage
After edging, use a stiff brush to remove clippings and dirt from the trimmer head and guard. Wet clippings left to dry can harden and damage the cutting mechanism. Let the tool cool before storing in a dry place. For gas models, run the engine dry if unused for more than a month to prevent fuel varnish from clogging the carburetor.
FAQs
Can any string trimmer edge a lawn?
Yes, virtually all string trimmers can edge by rotating the head or twisting the shaft to vertical. The technique relies on mechanical action, not a specific model. Trimmers with a dedicated rotating head switch are easier, but manual twisting works as well.
Why does my edge look uneven and wavy?
This is almost always caused by looking at the cutting head while walking instead of ahead. Your body drifts when staring down, producing a wavy line. Focus on a point 10 to 15 feet ahead and maintain a steady, brisk pace.
Should I edge before or after mowing?
Always mow first. Mowing sets grass to uniform height and makes the edge line visible. Edging over tall, uncut grass hides the boundary and can scalp grass, creating bare patches that take weeks to recover.
References & Sources
- ScottsMiracle-Gro. “How to Edge a Lawn.” Covers basic edging techniques and preparation steps.
- Troy-Bilt. “String Trimmer Tips and Techniques.” Details on trimmer orientation, movement direction, and safety.
- The Home Depot. “How to Use a String Trimmer.” General operation and edge-specific guidance.