Mower service — the 30 minutes that pays for itself every season

A sharp blade slices grass; a dull blade tears it. The cut you get from a serviced mower is visibly different from a neglected one — same lawn, same height, different finish.

Half an hour at the start of the season pays for itself across every cut after.

Why this matters

Grass cut by a sharp blade is sliced. The cut closes within a day, the leaf carries on photosynthesising, and the lawn looks crisp.

Grass cut by a dull blade is torn. The leaf tip frays. The exposed wound dries out. The frayed tip turns pale, then brown, then dies. Two days after a dull-blade mow, the entire lawn has a faint straw-coloured haze.

Sharp blade vs dull blade is the easiest cosmetic upgrade in lawn care. And the deck-and-oil routine that goes with it stops your mower from progressively getting worse over years until it stops one Sunday morning.

When to do it

• Once a season minimum. Spring is the natural moment — first mow of the year is a good prompt to service.
• More often if you mow large areas or rough ground (tree roots, stones, long grass once let go). Re-sharpen mid-season.
• Whenever the lawn shows a "frayed" cut — that straw haze a day or two post-mow is a dull-blade signal.
• Robot mowers — different routine. Quick spec at the bottom.

When not to do it

• Engine still hot — wait for it to cool fully before touching anything (oil drains, blade access). Engines have killed plenty of fingers.
• Battery in place (cordless) or plug connected (corded). Disconnect first, every time. A blade pin slipping while you're under the deck has a way of starting the motor.
• No spark plug removed (petrol). Same reason — accidental ignition.

How to do it (petrol rotary)

1. Cool engine, fuel below half, parked on a flat surface. Remove the spark plug before doing anything else — non-negotiable.
2. Tip the mower with the air filter / carb side up (otherwise oil leaks into the air filter and causes hard starts). Most modern mowers have a "service position" sticker.
3. Inspect the underside of the deck. Caked grass and moss build-up restricts airflow and reduces cut quality. Scrape clean with a putty knife or stiff brush. A pressure washer works on petrol mowers but dries the deck thoroughly afterwards.
4. Inspect the blade. Look for:
   • Visible dings, dents, or chunks → file flat or replace.
   • Dull edge (light reflects all along the cutting edge instead of "no reflection on the bevel") → sharpen.
   • Cracks → replace, do not sharpen. A failing blade at 3000 rpm becomes a projectile.
5. Sharpen the blade. File the bevel along the existing angle. Don't reshape it; the goal is to restore the original bevel, not to make it sharper than the design. A flat file run along the bevel a handful of times usually does it. Run a fingernail across the edge — should bite, not glide.
6. Re-balance. A balanced blade hangs flat on a nail through its centre hole. If one end dips, file a touch off the heavier end. Unbalanced blades vibrate the mower and shake the engine to bits.
7. Refit the blade (sharp side facing the rotation). Torque to the manufacturer's spec — check the manual; typical values for domestic petrol mowers fall in the 40–60 Nm range, but yours might differ. Loose blades fly off; over-tight blades shear bolts.
8. Change the oil (annual). Run engine 2 minutes to warm, switch off, drain into a container, refill with the manufacturer's recommended grade.
9. Replace the air filter if grey or oily. Swap, don't clean — paper filters degrade.
10. Replace the spark plug if the gap looks bad or it's been 2+ years. Cheap insurance.
11. Refit spark plug, refill fuel, test-start. Listen for vibration — if it shakes, blade balance is off; redo step 6.

How to do it (cordless / corded electric)

Same approach as petrol minus the engine work. Disconnect battery / unplug. Clean deck, inspect blade, sharpen or replace. Replace the battery if it no longer holds an hour's runtime — usually after 3–5 years.

How to do it (robot mowers)

Different beast — small razor blades on a rotating disc, run all the time on a charging dock.

1. Lift, flip, inspect the cutting disc weekly. Replace blades when chipped or dull (cheap; come in packs of 6 or 9).
2. Wipe the dock contacts monthly. Corrosion on the contact pins prevents charging.
3. Clean the wheels and chassis — debris in the wheel housings strands the mower and shortens motor life.
4. Update firmware when the app prompts — manufacturers fix navigation bugs in updates.
5. Boundary wire check annually — broken wires send the robot into bins or off the lawn.

What to expect afterwards

A serviced petrol mower starts on the first or second pull, runs without vibration, and produces a clean cut you can see immediately. The lawn looks tidier from the very next mow.

A neglected mower — dull blade, clogged deck, dirty filter — produces a fraying cut, vibrates uncomfortably, and sometimes won't start at all. The fix is usually 30 minutes; the misery from skipping it can last all summer.

Common mistakes

• Forgetting the spark plug. Don't put your hand under any mower without removing it.
• Sharpening to a razor edge. A grass-cutting blade wants a robust factory-style bevel, not a knife edge. Razor edges chip on the first stone.
• Skipping the balance check. Vibration is the slow killer of small engines.
• Tipping a petrol mower the wrong way. Oil into the air filter takes hours to clear.
• Cleaning a corded electric with a hose. Water and motor windings don't mix.
• "It still cuts." It cuts badly. The lawn knows. Sharpen.

Seasonal notes

Spring: full service before the first mow of the year. Sharpen, oil, filter, plug.

Summer: mid-season blade re-sharpen if you've cut heavy or hit anything hard.

Autumn: end-of-season clean before storage. Empty the fuel tank (petrol mowers) or run the carb dry — old fuel left in the tank gums up over winter.

Winter: store dry, away from frost (petrol). Battery mowers: charge the battery to ~50% and remove for storage somewhere cool.

Time for a sharper cut or a new mower?

A sharp, balanced blade transforms the cut from any mower. If yours is past saving, a reliable replacement — or a rear-roller model for a crisper finish — pays for itself across the season.

Related Mowd guides: UK Lawn Care Calendar · Summer lawn feed & wetting agent

Frequently asked questions

How often should I service my lawn mower?

At least once a year, ideally before the first cut of the season, with a mid-season blade sharpen if you mow large or rough areas.

How do I know if my mower blade is blunt?

If the lawn shows a pale, straw-coloured haze a day or two after mowing, the blade is tearing rather than slicing — time to sharpen.

Is it worth repairing an old mower or buying new?

If the deck is sound and it starts reliably, a service and new blade are well worth it. If it is unreliable, heavily corroded or underpowered for your lawn, replacing it is usually the better value.

Disclaimer

This is a general guide for typical UK domestic mowers. Specific procedures vary by model — always check the manual for blade torque, oil grade, and service intervals. Petrol mowers are mechanical equipment that can hurt you; if anything feels uncertain, take it to a service centre rather than guess.