A dull mower blade doesn't cut grass — it tears it. You end up with ragged, white-tipped edges that turn brown within a day or two, and your lawn looks worse than if you hadn't mowed at all. Sharpening your blades is one of the simplest maintenance jobs you can do, yet most people never bother.
I sharpen mine every 4–5 mows using a flat file — takes about 10 minutes. Once you've done it a couple of times, it becomes second nature.
As a rough guide, sharpen your blades every 20–25 hours of mowing. For most UK gardens, that works out at every 4–6 cuts during the growing season. If you're hitting stones, roots, or scalping bumpy ground regularly, you'll need to do it more often.
Signs your blade needs attention:
You don't need much kit for this job. Here's what I use:
If you prefer power tools, an angle grinder with a flap disc works brilliantly — just go steady. It's easy to remove too much metal if you're heavy-handed.
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Disconnect the spark plug lead (petrol mower) or remove the battery (cordless mower). This isn't optional — blades can rotate if the engine fires accidentally. Tip: I wedge a block of wood between the blade and the deck housing before loosening the bolt, so the blade can't spin.
Tilt the mower on its side (air filter facing UP on petrol models to avoid oil flooding the carburettor). Use a socket wrench to remove the central bolt. Mark the bottom of the blade with a bit of spray paint so you know which way it goes back on — fitting a blade upside down is more common than you'd think.
Scrub off all the caked grass, mud, and rust with a wire brush. You need a clean surface to see the actual condition of the cutting edge. This is also a good time to inspect for cracks — a cracked blade should be replaced, never sharpened.
Secure the blade in a bench vice. Using your flat file, follow the existing bevel angle — usually around 30–40 degrees. File in one direction only (push strokes, not back and forth). You're aiming for a butter-knife edge, not a razor. Too sharp and it'll dull faster and chip more easily.
Give each side roughly the same number of strokes. I count 15–20 per side as a starting point, then check.
This step matters more than most people realise. An unbalanced blade causes vibration that wears out bearings, spindles, and engine mounts over time. Place the blade on a balancer — if one side drops, file a little more off that end. You can also hang it on a nail through the centre hole; it should sit level.
Put the blade back on (painted side down), tighten the bolt firmly, and reconnect the spark plug or battery. Give the blade a spin by hand to check nothing catches.
Technically yes — you can use a drill-powered blade sharpener attachment that works with the blade still fitted. These are handy for a quick touch-up mid-season, but they won't give you as good a result as removing and filing properly. You also can't check balance without removing the blade.
For a proper job, remove it. For a quick five-minute refresh between full sharpens, a drill attachment is fine.
Sharpening can only do so much. Replace the blade if:
Replacement blades for most mowers cost between £10 and £25 — cheap insurance compared to the damage a failing blade can cause.
Both work. A flat file gives you more control and removes metal slowly, which makes it harder to over-sharpen. An angle grinder is faster but requires a lighter touch — it's easy to overheat the blade or remove too much material, which weakens the edge.
My preference: flat file for routine sharpening, angle grinder for blades that are badly nicked or haven't been sharpened in a long time.
A sharp blade is the single easiest way to improve the quality of your cut. Ten minutes with a file, and your lawn will look noticeably better the very next mow.
