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HOW-TO GUIDEWhy Your Lawn Mower Leaves Strips of Uncut Grass
Stripes of standing grass left behind after a pass almost always come down to one of three things: a blade that is no longer cutting cleanly, a deck that cannot move air properly, or the way you are walking the mower. Nine times out of ten it is a blunt blade or passes that overlap too little, and both are fixable in an afternoon.
Flymo Lawn Mower Review
If your mower struggles on longer or damp grass however you set it up, our Flymo breakdown covers cutting width, deck design and where these machines run out of puff.
See Our Top Pick →Start with the blade
A mower blade does not slice grass the way a knife does. It relies on speed and a sharp leading edge to shear each stem off cleanly. Once that edge rounds off, the blade pushes grass over instead of cutting it, and anything that lies flat pops back up behind you as a strip.
Tip the mower on its side (fuel cap upward on a petrol machine, battery or plug removed first) and run a gloved finger along the cutting edge. Rounded, nicked or dented by stones, and that is your answer. A blade that has met a buried root can also bend slightly, dropping one end lower than the other and producing a repeating uncut band.
Sharpening is straightforward with a file or a bench grinder, but the blade must stay balanced. Take the same amount off each end, then check by hanging the blade on a nail through the centre hole. If one side dips, take a little more off it. An unbalanced blade vibrates, and vibration wrecks spindle bearings over a season.
You are cutting too much off at once
The old advice about never removing more than a third of the grass height still holds. When the lawn has run away from you, the mower is cutting and lifting a huge volume of clippings at once. The deck fills, airflow dies, and grass that never got pulled upright is simply flattened and missed. Raise the deck a couple of notches, cut once high, leave it a day or two, then drop back to your usual height.
Your walking speed is beating the blade
The blade only gets so many rotations per metre of travel. Push faster and each patch of grass sees fewer passes of the cutting edge, so anything springy or lying at an angle gets missed. This catches out self-propelled mowers in particular, where the drive is set brisk and the operator just holds on. Slow down by a third on thick or damp grass, and treat a dropping motor note as a sign you are already overloading it.
Quick Tip
Overlap each pass by about a quarter of the cutting width, not just an inch or two. Most mowers cut slightly narrower than the deck suggests, and wheel tracks push grass down just outside that line. A generous overlap covers both.
The deck is clogged underneath
Cut grass, especially damp grass, cakes onto the underside of the deck in a thick mat that kills the airflow the mower depends on. A rotary blade creates a vacuum that lifts grass upright before cutting it, so once the deck is packed, the lift disappears and lying stems survive the pass untouched.
Disconnect the power or spark plug lead, tip the mower and scrape the deck out with a plastic scraper. Do this every few cuts rather than waiting for the buildup to become obvious. It also holds off the corrosion that eventually eats through a steel deck.
A packed grass box does the same thing from the other end. Once the box is full, clippings recirculate inside the deck instead of leaving it, and you get streaks of dropped clippings alongside patches that were never cut properly. Empty it earlier than feels necessary on the first cut of spring.
Wet grass simply will not stand up
Damp grass sticks together and lies flat under the mower's own airflow. Raising the height and slowing down helps, but only so far. If a lawn is genuinely wet the honest answer is to wait: mowing it loads the motor, clogs the deck faster and leaves clumps that smother the grass underneath.
Uneven deck height
On mowers with individual wheel adjusters it is easy to knock one wheel to a different setting without noticing, leaving the deck at an angle: cutting properly on one side, riding high on the other. Check every adjuster reads the same number, and on single-lever machines check for unevenly worn wheels or a missing spacer.
Blade speed has dropped
If the mechanical checks come up clean, the blade may not be spinning fast enough. On petrol mowers that usually means the engine is not reaching full revs, often from a dirty air filter or stale fuel. On cordless mowers a tired battery sags under load and the motor throttles back. On belt-driven machines a stretched or glazed belt slips the moment the blade meets resistance. All three show the same symptom: fine on thin grass, strips the second the lawn gets thick.
Work through it in order
- Inspect and sharpen the blade, checking for bends and balance.
- Scrape the underside of the deck clean.
- Confirm all wheels or the height lever are set evenly.
- Raise the cutting height one notch and slow your walking pace.
- Overlap passes by a quarter of the deck width.
- If strips remain, look at battery condition, air filter, fuel or drive belt.
Most lawns come right at step one or two. The later steps matter when a mower that used to cut fine has slowly got worse over a couple of seasons.
Why does my mower only leave strips in one part of the lawn?
That usually points at the lawn rather than the mower. Shaded or damp areas grow softer, floppier grass that lies down instead of standing up, and a dip in the ground lets the deck ride over the top. Mow that section higher and in a different direction.
Can a new blade still leave uncut strips?
Yes. A blade fitted upside down barely cuts, and it happens more often than people admit. The wings or lifted edges should face up toward the deck, not down toward the grass.
Does mowing in a different direction each time help?
It does. Mowing the same way every week trains grass to lean in one direction, and grass leaning away from the blade is much harder to cut cleanly. Alternating between cuts keeps it upright and gives a more even finish.