How to Recut a Natural Bed Edge with a Bed Edger

Why this matters

A natural bed edge (a cut trench between turf and a mulched bed, no plastic, steel or stone) is the cheapest edging a customer can have and the one that disappears fastest. Turf rhizomes and stolons creep across it, mulch slumps into it, and by midsummer the bed line has wandered into a soft, lumpy border that makes a fresh mow look careless. Recut properly once or twice a season with a powered bed edger, the edge holds a crisp shadow line for months. Recut badly, with a sloped turf wall or the wrong depth, it is back to a blur in weeks and the crew is redoing the same feet every visit. Weekly walk and drive edging with a stick edger or trimmer belongs to Edging and Trimming Best Practices; this card is the trench itself.

The shape you are cutting

The edge works because of its geometry. The turf side is a vertical wall, so grass roots that grow outward meet air and stop, and a trimmer or stick edger has a clean face to follow on weekly visits. The bed side slopes back to the mulch, so mulch does not slump into the trench and the soil face does not collapse. The trench bottom gives the shadow line that reads as a crisp edge from the street.

 CROSS SECTION OF A SPADE-CUT NATURAL BED EDGE

   TURF SIDE                         BED SIDE
   grass
   ||||||||||
   ----------+                         mulch, held
             |                    ____ about 1 in
   vertical  |  3 in             /     below the
   turf wall |  deep        ___/       turf line
             |         ___/
             +_______/  bed side sloped back
              trench    about 45 degrees
              bottom

Depth is a shop setting: 3 in on the turf wall is a common default that is deep enough to stop most creeping turf for a season and shallow enough that a mower wheel dropping into it does not jar or tip the machine. Deeper than about 4 in starts cutting into feeder roots of shrubs planted near the edge and leaves a trip hazard on a lawn people walk across.

Start state: before the blade goes in

• Utilities. A bed edger cuts 3 to 4 in into soil, which is where low-voltage lighting wire, drip irrigation tubing, invisible pet-fence wire and shallow irrigation laterals live. Those are private lines and the one-call (811) locate service does not mark them, so ask the customer, look for fixture and valve locations, and flag them before you cut. Whether a state's one-call law requires notice before shallow mechanized digging, or exempts it, varies by state; on any new bed line, or any edge deeper than the existing one, check your state's law and call before you dig if it applies. If the blade hits a wire or a pipe, stop the engine, let the blade stop, and look before pulling it free.
• The machine. Blade sharp and secure, guard in place, depth stop and blade tilt set. Fuel it on the trailer or the hardscape with the engine off and cool, not on the lawn, and wipe spills.
• PPE and bystanders. Safety glasses (a bed edger throws soil and stones hard and low), hearing protection, boots with toe protection, long pants. People and pets kept well clear of the discharge side, at least the distance the maker's manual states.
• The line is agreed. On an existing bed, the old line is the line unless the customer asks for a change. On a new curve, the customer approves a hose or string layout first.

The steps

1. Lay out new curves with a hose or string, then paint it. A garden hose lies in a natural curve; walk the customer to the spot they look from (usually the front walk or a window) and move it until they like it, then mark the line with turf paint and pull the hose. Reason: a curve that looks smooth from where you stand can look kinked from the house, and you cannot uncut a trench.
2. Set the depth on a test cut. Set the depth stop to the shop setting, cut 2 ft somewhere inconspicuous, and measure the turf wall with a rule from the turf soil surface to the trench bottom. Adjust and re-cut until it reads the target. Reason: depth stops are marked loosely, soil firmness changes how deep the blade rides, and the first 2 ft is the cheapest place to find out.
3. Set the blade tilt so the turf side is the vertical side. Most bed edgers tilt the blade or cut a beveled trench; run the machine so the vertical face falls on the turf side and the bevel falls on the bed side. Check with a square against the turf wall on the test cut. Reason: a turf wall that leans back toward the lawn becomes a ramp for stolons and a mower wheel; a vertical one holds for months.
4. Cut with the machine, not against it. Walk slowly and let the blade work at a steady depth. On curves, take tight radii in short, overlapping bites instead of forcing the machine around. Keep both hands on the controls. If the blade catches a root or a rock and the machine kicks or climbs, release the drive, let it settle, and lift and reset past the obstruction. Tree roots over about an inch thick are cut cleanly by hand with loppers or a pruning saw, or the line is moved to miss them; a tree's structural roots are not something a bed edger tears through.
5. Clear the spoil the same day. The turf chunks and soil the blade throws go out, not into the bed. Rake them into a wheelbarrow and haul them off or to the customer's compost. Reason: turf chunks tossed into the bed root and become the next weed problem, and loose soil in the trench softens the shadow line immediately.
6. Clean the turf wall and trench by hand. A flat spade or half-moon edger trues up any stretch where the machine wandered, squares the wall, and pulls out runners the blade cut but did not remove.
7. Top the bed back to the line. Pull mulch back from the trench so it sits about 1 in below the turf surface along the slope, not heaped against the turf wall. Add mulch where the bed was thin. Reason: mulch piled level with the turf fills the trench in one rain and invites the turf to grow straight into it.
8. Blow off and walk it. Blow soil off walks and drives back into the bed, not into the street or a storm drain. Walk the full length and fix any stretch that fails the finish checks below.

Worked example: a 140 ft bed perimeter with one new curve

A front bed has 140 ft of natural edge, grown in about 2 in at its worst. The customer wants a 30 ft stretch along the walk reshaped into a wider curve. Low-voltage lighting runs along the house side of the bed.

Layout. Hose laid, customer approves the curve from the front door, line painted. The lighting wire is traced from the transformer to the fixtures and flagged; it runs well inside the bed, clear of both the old and new lines. The new curve is a new bed line, so the shop checks the state one-call rule and files a locate ticket before the visit, as the state requires for this work.

Test cut. Stop set to "3". The first 2 ft measures 2.5 in on the turf wall; firm, dry clay is riding the blade up. Stop lowered one notch, re-cut, 3.0 in. Square against the wall: vertical.

Spoil estimate. Treat the trench as a right triangle in section (the real cut has a narrow flat bottom, so this runs slightly low): 3 in deep on the turf wall and 3 in wide at the top where the 45 degree slope meets the bed. Area is half of 3 times 3, 4.5 sq in, which is 4.5 divided by 144, about 0.031 sq ft. Over 140 ft that is 140 times 0.031, about 4.4 cu ft of soil, before the cut turf from the 2 in of creep. That is most of a 6 cu ft wheelbarrow, so the crew brings the barrow and a tarp rather than planning to scatter it. Check from the other direction: 4.5 sq in times 12 in is 54 cu in per foot; 54 times 140 is 7,560 cu in, divided by 1,728 cu in per cu ft, 4.4 cu ft. The two agree.

Cutting. The old line is followed at a slow walk for 110 ft; the new 30 ft curve is cut along the paint in short bites at the tight end. One 1.5 in root from a nearby maple crosses the new line; the edger is lifted past it and the root cut cleanly by hand with a saw rather than torn.

Finish. Turf wall measured every 10 ft along the 140 ft: 14 readings from 2.75 to 3.25 in, all within 1/4 in of the target. Mulch pulled back about 1 in below the turf line. Hardscape blown back into the bed.

How to verify the edge

• Depth: 3 in, plus or minus 1/4 in, measured at the turf wall every 10 ft.
• Wall: vertical against a square on the turf side, no lean back toward the lawn.
• Line: smooth when sighted from the customer's viewing spot; no flats on curves, no kinks where a bite started.
• Clean: no turf chunks in the trench or the bed, no soil on hardscape, mulch below the turf line.

What changes the method

Bed meets hardscape, or the bed has a steel or plastic border. That is not a natural edge; do not run a bed edger along steel edging, which can catch and throw it. See related: Hardscape Edging Installation.

Wet or saturated soil smears instead of cutting, leaves a rounded wall, and the edger's wheels rut the lawn. Reschedule rather than cut a wall that will slump.

Sandy soil will not hold a vertical wall as long. Expect to recut more often and consider a slightly shallower trench so the wall stands.

A heavily overgrown edge, more than a few inches of creep, takes two passes: one to cut the new line and a second with the depth reset to clean the strip of turf between the old and new lines, then a hand pass to lift the sod.

References

• See related: Edging and Trimming Best Practices, for weekly walk and drive edging.
• See related: Hardscape Edging Installation; Spring Mulch Refresh.
• Your state's one-call (811) law, for when notice is required before mechanized digging and what it does not mark (private lines).
• Manufacturer operator's manual for the bed edger, for depth and tilt adjustment, bystander distance and safe operation.