How to Trim a Hedge Straight (Without a String Line)
You walk past hedges every day in Aussie suburbs that look like a brick — flat top, flat sides, sharp corners, string-line straight. Technically straight, sure, but hedges are plants not bricks and a brick-shaped hedge looks weird in an Aussie garden. The good ones — the ones at high-end Cottesloe or Toorak houses — are gently undulating, slightly tapered, and look natural even though they’re carefully shaped. That look comes from the eye, not from a string line. The trick is what I call the “step-back-every-3-metres” method. You trim a section, walk back, look at it from five metres, adjust, move on. Takes longer than running a string and slashing through it, but the result looks like a designer hedge not a fence. Worth doing once, worth doing right.
The other thing nobody tells you in Australia is that when you trim matters more than how. Lillypilly — the most popular hedge in Aussie gardens — has a psyllid season. Get the timing wrong and you spread those leaf bumps across all the new growth. I’ve seen $2,000 hedges ruined by a March trim done at the wrong moment.
What you’ll need
- Battery hedge trimmer — Ozito 18V or Ryobi One+ are fine for a home hedge; Stihl HSA 60 if you’ve got 30+ metres
- Sharp secateurs — Felco 2 or Felco 6 (the genuine ones, not the Bunnings copies — copies go blunt in a season)
- A drop sheet or old tarp to catch trimmings
- Step ladder — NOT an A-frame on grass. Use a tripod orchard ladder if you have one, or work off something solid. AS/NZS 1892 rules apply.
- Safety glasses and ear protection — non-negotiable
- Garden gloves
- Yates Confidor (psyllid spray) if your lillypilly is already bumpy
Step 1: Identify your hedge species
Different hedges, different rules:
- Lillypilly (Syzygium): trim in October and again in late March, AFTER psyllid activity drops
- Murraya: trim after each flush of flowers (May, September, January) — they bounce back fast
- Photinia (Red Robin): trim early spring and again in summer to keep the red tips coming
- Buxus (English box): two trims a year, May and October — slow grower, light hand
- Westringia (native rosemary): never cut into bare wood — it wont shoot back. Light tip-prune only.
Step 2: Time it around psyllid (lillypilly only)
Here’s the Aussie gotcha. Lillypilly psyllids cause those hard pimple-like bumps on the leaves. They lay eggs on NEW growth. If you trim during peak psyllid activity (typically February and August in most of Australia), all the fresh new shoots get hit and your hedge becomes one big bumpy mess. Trim AFTER psyllid season — late March and late September are the safe windows in most parts of the country. If your hedge is already bumpy, spray with Yates Confidor four weeks before trimming to break the cycle.
Step 3: Set the height with a single anchor point
Don’t string-line. Pick the lowest acceptable height somewhere along the hedge — usually the lowest point of an existing top, or a level you’ve decided on. Mark it with a stake. That’s your anchor. Every other height decision references that one point with the eye, not with string. Eye-level vision works better than string for one simple reason: the eye corrects for slight ground rise and fall the way a string line cant.
Step 4: Trim the top first, in 2-metre sections
Hedge trimmers cut best when held flat and swept in long arcs. Start at one end. Trim a 2-metre section to the height of your anchor stake. Stop. Walk back five metres. Look at it square-on and from each side. Adjust if it’s not right. THEN move to the next 2-metre section. This is the bit weekend-warriors skip and its why their hedge looks like a saw-tooth. The eye picks up height variations of 20mm at distance that you cannot see from arm’s length.
Step 5: Taper the sides — wider at the bottom
This is the second secret to a good-looking hedge. The sides should taper IN slightly toward the top — say 50mm narrower at the top than the bottom over a 1.5m hedge. This lets light reach the bottom of the hedge so the lower leaves don’t go thin and woody. Brick-shaped hedges (parallel sides) inevitably go bald at the bottom within three years because the top shades the bottom. Tapered hedges keep their full foliage right to the ground.
Step 6: Cut sides in vertical sweeps
Hold the trimmer vertically — blade pointing down, then up alternating — and work bottom-to-top in sweeps. Don’t try to cut top-to-bottom in one go. Gravity drags the trimmer in and you cut a divot. Bottom-up gives you control of the line. The trick my old man showed me on his Murraya hedge in Mandurah years ago was to imagine the blade is buoyant — it wants to rise, so let it. Press in too hard and you’ll dig in.
Step 7: Step back. Step back. Step back.
Every three metres of progress, walk back five metres minimum, ideally eight. Look at the hedge in profile. Look at it from the angle people see it from when they walk up the path. The eye is the only level that matters. Mark any high spots with a peg of bamboo and come back to them after the rough cut. Sounds tedious. Adds maybe ten minutes to the job. Result looks twice as professional.
Step 8: Detail with secateurs
Hedge trimmers leave torn edges on big leaves — lillypilly, murraya, photinia all show ragged cut leaves for weeks. Walk along the hedge with secateurs and cleanly snip every leaf the trimmer ripped, just back of the rip. Tedious work but worth it. The hedge will look immaculate within a week instead of looking shredded for a month. This is what separates a $300 council trim from a $2,000 designer trim — clean leaf edges.
Step 9: Clean up trimmings same day
Lillypilly leaves on a lawn become slippery when wet and rake-resistant once they bond into the grass. Drop sheet under the hedge while you trim, then bag everything immediately. Council green-waste bin if you have one, or a trip to the tip. If you’ve got a chipper or a mulcher, the trimmings make good mulch for garden beds — but lillypilly leaves take a while to break down so dont use them around veg beds.
Step 10: Feed and water after trimming
A heavily trimmed hedge has lost its food-making leaves. Give it a handful of slow-release Osmocote or Searles Robust per metre and a deep water. Two weeks later it’ll throw a vigorous flush of new growth. This is also the moment to apply Confidor if you’re a lillypilly owner with psyllid history — preventing the next round of bumps before the new growth gets hit.
When to call a tradie or pro
If your hedge is over 3.5 metres tall, get an arborist or a specialist hedge contractor. Working off a tall A-frame ladder on uneven ground holding a hedge trimmer is exactly how the AS/NZS 1892 ladder fatalities happen. Ladder safety rules are non-negotiable above 2.5m working height. If your hedge butts up against power lines, that’s licensed work — only level-2 vegetation contractors can trim near live lines (1m clearance rule in most states). Boundary hedges in a dispute with a neighbour are a council/legal matter — don’t go cutting their side without written consent. And if a hedge is dead at the base and you’re hoping a hard prune will revive it, get a horticulturist or an arborist to assess first — some species genuinely don’t come back from bare wood.
Common screw-ups
- Trimming lillypilly during psyllid season: all the new growth gets hit. Trim outside the windows.
- Parallel-sided “brick” hedges: go bald at the bottom in three years. Always taper.
- String-line trimming: the eye is a better level than string for hedges. Walk back.
- A-frame ladder on grass: ladder fatality waiting to happen. AS/NZS 1892 says level firm ground only.
- Hard pruning westringia or buffalo runners: wont shoot from bare wood. Light hand only.
Cost & time
Battery trimmer Ozito or Ryobi $130-200, Stihl HSA 60 $400. Secateurs Felco 2 $90. A 15-metre hedge run is about 90 minutes for the cut plus 30 minutes for secateur detail and cleanup. Pro hedge contractors charge $80-150 an hour in Perth, similar in Sydney and Melbourne, plus disposal.
Battery vs corded vs petrol — what to actually buy
For a home hedge under 30 linear metres, an Ozito 18V or Ryobi One+ battery trimmer is plenty. They’re cheap, they share batteries with your other tools, and they cut beautifully. Above 30 metres or for thicker stems (lillypilly stems over 8mm) you’ll appreciate a Stihl HSA 60 (battery, $400) or HS 56 (petrol, $500). Corded electric trimmers exist but the cord is a pain on a lawn — I havent bought a corded one in eight years and I dont miss it. Sharpen the blades once a season with a Stihl chainsaw file (small round file) drawn along each tooth. Blunt trimmer blades tear leaves rather than cut them — same problem as a blunt mower blade. Curved and shaped hedges need the step-back method even more — string lines simply cant do curves. Mark waypoints with small bamboo stakes at each high and low point of the curve, then trim between them, stepping back constantly to verify the curve flows smoothly.
Step back every three metres. Trim lillypilly outside psyllid windows. Taper the sides slightly. Detail with secateurs after the trimmer. Do those four things and your hedge will look like a pro did it even if you’ve never trimmed one before. String lines are for fences, not for plants. While youre out there with the secateurs, see if your lawn needs attention too, and if you havent serviced the petrol mower recently, knock that out same morning. No dramas.
