Long grass is the job that clogs more brush cutter heads than brambles, nettles, or anything woody. The fix is almost never a stronger machine — it’s cutting it in the right order, at the right speed, in the right shape of pass.
Why long grass clogs the head
Grass over roughly 30-40 cm bends under its own weight instead of standing upright to meet the line or blade, so a rotation through it does far more cutting work than the same length of short, upright grass would need. Cut stems from tall grass are also longer and more tangled, so instead of being flung clear they catch on the spool, gearbox housing, or guard edge and start wrapping. Once a few strands catch, every following rotation adds more, and a clean-spinning head can pack solid within seconds.
Two things make this worse: cutting the full height in a single pass, and letting revs drop as the load increases. Both are fixable with technique, not equipment.
The two-pass method: top then base
This is the single biggest fix for clogging in long grass, and it costs you almost no extra time overall because a clogged head costs far more in stopping, clearing, and restarting.
- First pass — top the growth. Run the head or blade through the upper third to half of the grass height only, without trying to reach ground level. This removes the bulk of the material — seed heads and top growth — that would otherwise overload the head on a single deep pass.
- Let cut material fall clear. Give the topped grass a second to drop before running back through the same line; long clippings settle slower than short ones.
- Second pass — cut to finish height. With most of the bulk gone, take the remaining stubble down to your target height (commonly 5-10 cm for general clearance). The load on the attachment is now a fraction of what a single full-height pass would demand.
- Repeat per strip, not per field. Top and finish one strip before moving to the next — grass topped and left standing can spring back up over an hour or two.
Don’t push a blade or line harder into grass that’s bogging it down. If the attachment visibly slows and the engine note drops, ease off, back out, and let the head clear before going back in — a blade that suddenly breaks free from a jam under load can kick back hard.
Keep the revs high
Long grass punishes low engine speed more than almost any other cutting condition, and this is where most clogging actually starts.
- Cut at or near full throttle. A line or blade needs enough rotational speed to fling cut grass clear by centrifugal force before the next stem arrives; drop below that and clippings simply accumulate.
- On a typical 25-35 cc petrol brush cutter, idle sits around 2,800-3,200 rpm and working speed is several thousand rpm above that — if you hear the note dropping toward idle as the head meets grass, back out rather than holding position and waiting for it to cut through.
- On a battery machine, use the higher of the available power settings for long grass. The reduced torque on an eco or low setting is exactly what lets long, heavy grass overpower the head.
- Resist the instinct to throttle back “to be gentler.” An engine built to run at working speed isn’t protected by idling through resistance — it’s doing the same cutting work with less energy behind it, which is what causes bogging.
Cut in strips, not random passes
Working method matters as much as throttle. Move across the area in overlapping strips, always advancing into grass that’s full height on only one side rather than both.
- Choose a starting edge and cut a strip roughly one head-width wide, moving in a steady sweeping arc.
- Overlap the next strip by a few centimetres into the stubble already cut.
- Keep advancing in the same direction rather than jumping between untouched patches — random passes mean cutting full-height grass on both sides of the head, doubling the load compared with a strip that’s already half-cleared.
- On sloped ground, cut strips across the contour where footing allows, rather than up and down, so you’re not fighting the slope and full-height grass at once.
Clearing build-up under the guard
Even with good technique, cut grass builds up under the guard and around the head over a working session. Left unchecked, it adds drag, unbalances the head, and eventually stops it cutting at all.
- Stop the engine, or release the trigger and remove the battery on electric machines.
- Wait for the line or blade to come to a complete stop before touching anywhere near it.
- Use a stick, scraper, or gloved hand to pull packed grass out from under the guard and off the gearbox housing.
- Check the spool base or blade hub itself, not just the visible guard — grass wound tightly around the bolt is easy to miss and adds real imbalance.
- In heavy long grass, clear it every 10-15 minutes rather than waiting until cut quality visibly drops.
Always fully stop the cutting attachment and disconnect the power source before reaching near the guard. Packed grass can hide a blade edge, and a head restarting unexpectedly while your hand is near it is a serious injury risk.
Line or blade: which clogs less in long grass
| Attachment | Behaviour in long grass | Best for |
|---|---|---|
| Bump-feed line, 2.0-2.4 mm | Whips through light growth well but wraps quickly once grass is tall or dense; needs frequent clearing | Light long grass, finish trimming after topping |
| Bump-feed line, 3.0 mm+ | Sheds slightly better than thinner line due to added mass and stiffness, but still wraps under sustained load | Medium long grass where a blade isn’t fitted |
| 3-tooth or 4-tooth blade | Slices stems on contact rather than relying on whip speed; sheds long grass far better than line and rarely wraps | Long, dense, or matted grass generally |
| 8-tooth or brush blade | More aggressive cut, copes with woody stems mixed into the grass | Long grass with brambles or scrub mixed in |
If clogging is a recurring problem, fitting a 3-tooth or 4-tooth blade over a line head solves most of it outright — a replacement blade is typically a €15-30 part and pays for itself in avoided stoppages within a single session on rough ground.
Avoid wet grass where you can
Wet grass — from rain, dew, or shade holding overnight moisture — clogs faster than the same grass dry, because cut stems stick to each other and to the head instead of separating and flying clear. If the job can wait an hour for dew to burn off, or a day for rain to dry out, you’ll cut faster and clog less than pushing through it wet. Where it can’t wait, clear the guard more often — every 5-10 minutes rather than 10-15 — since wet build-up packs tighter and faster than dry.
Quick checklist
- Top tall growth first, then cut to finish height in a second pass — never take full-height long grass down in one go.
- Keep revs at or near full throttle throughout; back out of bogging grass rather than pushing through it.
- Work in overlapping strips in one direction, not random passes across the area.
- Stop the engine and clear packed grass from under the guard every 10-15 minutes in heavy growth.
- Fit a 3-tooth or 4-tooth blade if clogging is a recurring problem with a line head.
- Cut dry where the schedule allows it; wet grass clogs faster than dry grass every time.
When to call a dealer
None of the above is a workshop job — it’s technique and routine clearing that any operator can manage. Get a small-engine mechanic or dealer to look at the machine if the head keeps clogging or the engine keeps bogging at full throttle with a blade fitted and no build-up under the guard, since that pattern often points to a carburettor that’s no longer set correctly for load rather than anything about the grass itself. A gearbox that’s noticeably hotter than usual after clearing sessions, or a head that won’t spin freely once cleared, is also worth having checked rather than worked around.