Cutting and keeping a lawn edge
Cut the line once, then trim to it. The two jobs need different tools and mixing them up is what moves the edge.
Cutting an edge and trimming an edge
Cutting a new edge means slicing vertically down through the turf to define where the lawn stops. That is done once or twice a year with a half moon iron, and it removes a strip of turf.
Trimming means cutting the grass that has grown out horizontally over that line. That is done every few weeks with shears held vertically, and it removes only leaf. Doing the first job when the second was needed is why a border is 100mm wider than it was three years ago.
- Cut once or twice a year
- A half moon iron, slicing vertically. It defines the line and removes turf.
- Trim every few weeks
- Edging shears held vertically. It removes overhanging leaf and nothing else.
- Never recut monthly
- Each cut moves the line a few millimetres inward, and after three years the bed is much wider.
- Spring for the cut
- Once growth starts, so the edge knits back rather than sitting raw all winter.
Getting the line right
For a straight edge, work against a plank or a taut string line. A half moon iron follows whatever it is placed against, and freehand over five metres wanders visibly even when each individual cut looks fine.
For a curve, lay a hosepipe on the grass and adjust it until the shape looks right from the house rather than from where you are standing. Then cut along it. A gentle continuous curve reads as deliberate; a series of shallow arcs reads as a mistake.
- Plank or string for straight
- The iron follows what it is against. Freehand over five metres always wanders.
- Hosepipe for curves
- Adjust the shape on the ground until it looks right, then cut to it.
- Judge it from the house
- Not from where you are kneeling. That is the view the shape will be seen from.
- Fewer, longer curves
- One sweeping curve beats four shallow ones, and it is much easier to mow around.
The cut has to be vertical
An edge cut at an angle undercuts the turf, so the overhang dries out, dies back and crumbles within a season. Then the line has to be recut, which is how the border creeps.
Keep the blade vertical and step down on it with your full weight rather than pushing with your arms. The depth wants to be around 75mm to 100mm, enough to cut through the root mat and into the soil below it.
- Vertical, not angled
- An undercut edge dries out and crumbles, and then it needs recutting. That is the creep.
- 75 to 100mm deep
- Through the root mat and into the soil. Shallower and the grass roots straight back over.
- Step, do not push
- Your body weight does the work. Pushing with your arms gives a shallow angled cut.
- Remove the strip
- Lift the cut turf out rather than leaving it. Left in place it re-roots and the edge closes up.
Gutter edges and hard edges
A cut edge with a small trench behind it, sometimes called a gutter edge, keeps grass from creeping into the bed and gives a shadow line that reads crisply from a distance. It needs recutting annually and it looks like professional work.
A hard edge, meaning a brick, timber or metal strip set flush with the lawn, removes the job almost entirely. It costs more to install and then a mower runs straight over it and no edging is needed at all. On a lawn you intend to keep for years it is the cheapest option overall.
- Gutter edge for looks
- A shallow trench behind the cut gives a shadow line, and it needs recutting annually.
- Hard edge to remove the job
- Metal, timber or brick flush with the turf. The mower runs over it and nothing needs trimming.
- Set it flush, not proud
- A proud edging strip scalps the mower blade and shows as a bald line along the lawn.
- Cheapest over time
- A hard edge costs more once and saves the annual cut and the fortnightly trim thereafter.
A sharp iron does the job in half the time
A half moon iron is a cutting tool and almost nobody sharpens one. A blunt one tears through turf and needs real force; a sharp one slices with your weight alone and leaves a clean face that knits back quickly.
The same is true of edging shears. They cut grass, which is soft and springy and therefore unforgiving of a dull edge, so a blunt pair pushes the grass over rather than cutting it and it springs back up uncut.
- File the iron
- A few strokes along the leading edge. It halves the effort, and hardly anyone does it.
- Clean off the sap and soil
- Both hold moisture against the steel, and a pitted blade drags in every cut afterwards.
- Shears need a tight pivot too
- A loose pivot lets the blades part, and no amount of sharpening fixes that.
- Brown tips mean blunt
- If cut grass browns at the tip within a day or two it was torn rather than cut.
Frequently asked questions
- What tools do I need to edge a lawn?
- A half moon edging iron for cutting the line, and a pair of long handled edging shears for trimming the overhang between cuts. That is genuinely all most lawns need. Add a plank or string line for straight runs and a hosepipe for setting out curves.
- What is a half moon edging iron?
- A crescent shaped blade on a shaft, pushed vertically down through turf with your foot to cut a clean line. The curve lets you rock it along the line, which is what gives a continuous edge rather than the scalloped one a straight spade blade leaves.
- How often should I edge a lawn?
- Cut the line once or twice a year, usually in spring. Trim the grass that grows out over it every few weeks through the growing season. Cutting a fresh line every month is the reason borders end up considerably wider than they were originally.
- How deep should a lawn edge be cut?
- Around 75mm to 100mm, deep enough to go through the root mat and into the soil beneath. Any shallower and the grass simply roots back across the line within a few weeks, so the work does not last.
- Why does my lawn edge keep crumbling?
- Almost certainly because the cut was angled rather than vertical, which undercuts the turf. The unsupported overhang then dries out, dies back and crumbles away. Keep the blade vertical and step down on it with your weight rather than pushing with your arms.
- How do I cut a curved lawn edge?
- Lay a hosepipe on the grass and adjust it until the shape looks right viewed from the house rather than from where you are standing, then cut along it. One long sweeping curve looks deliberate and mows easily; several shallow arcs look like a mistake.
- Are rotary lawn edgers any good?
- On a long straight run, yes, and they are quicker than shears. A star wheel rolled along the edge slices and lifts the overhang in one pass. They will not follow a tight curve, and they do not cut a new line, so a half moon iron is still needed for that.
- Is it worth installing a hard lawn edge?
- On a lawn you intend to keep for years, yes. A metal, timber or brick strip set flush with the turf lets the mower run straight over it, which removes both the annual cut and the fortnightly trim. It costs more once and less over time. Set it flush, never proud.
