A lawnmower is one of the most expensive tools most of us keep in the shed, yet it is also one of the most neglected. We tend to wheel it out, cut the grass, and wheel it straight back in without a second thought – until one spring morning it refuses to start, smokes like a bonfire, or leaves the lawn looking ragged. The good news is that the vast majority of mower problems are completely avoidable. A little regular care keeps your machine starting first time, cutting cleanly, and lasting far longer than the warranty.
In this guide we walk you through everything you need to keep a lawnmower in top condition, whether you own a petrol model, a cordless battery mower, or a corded electric one. We cover cleaning, blade sharpening, oil changes, spark plugs, air filters, battery care, and a season-by-season schedule tailored to the UK climate. None of it is complicated, and most jobs need only basic tools and half an hour of your time.
Why lawnmower maintenance matters
Skipping maintenance does not just risk a breakdown – it costs you money and gives you a worse lawn. A blunt blade tears grass rather than slicing it, leaving frayed, browning tips that invite disease and make the whole lawn look dull. A clogged air filter or fouled spark plug forces a petrol engine to work harder, burning more fuel and shortening its life. Old oil loses its protective qualities and lets internal parts wear prematurely. By contrast, a well-maintained mower starts on the first or second pull, sips fuel, and can easily last fifteen to twenty years.
There is a safety angle too. Mower blades spin at enormous speed, and a cracked or loose blade is genuinely dangerous. Taking five minutes to inspect the underside of your machine is time well spent.
Safety first: always isolate the power
Before you touch the underside of any mower, make sure it cannot start. This is the single most important rule in this guide.
- Petrol mowers: remove the spark plug cap (the rubber boot that pushes onto the spark plug). With no spark, the engine cannot fire even if the blade is turned.
- Cordless mowers: remove the battery completely and, where fitted, take out the safety key.
- Corded electric mowers: unplug from the mains at the socket, not just at the mower.
Wear sturdy gloves whenever you handle the blade, and tip petrol mowers with the spark plug side uppermost so oil and fuel do not flood the air filter or carburettor.
The basic maintenance kit
You do not need a workshop full of tools. A modest kit covers almost every job:
- A pair of cut-resistant gloves and safety glasses.
- A stiff brush or plastic scraper, plus an old paintbrush for fiddly areas.
- A flat metal file or a dedicated blade sharpener for keeping the cutting edge keen.
- A socket set or spanner to undo the blade bolt, and a spark-plug spanner for petrol models.
- The correct engine oil (most four-stroke UK mowers use SAE 30 or 10W-30), a fresh spark plug and air filter, and a small oil-drain tray.
A simple sharpening file costs only a few pounds, while a guided sharpener such as an Oregon blade sharpener or a multi-slot tool from a brand like SHARPAL gives more consistent results for around £20–£40. If you are still choosing a machine, our guide on how to choose a lawnmower and our best petrol lawnmower and best cordless lawnmower round-ups will point you in the right direction.
Step 1: Clean your mower after every cut
Cleaning is the most valuable habit you can build, and it takes only a couple of minutes. Grass clippings trap moisture against metal, encouraging rust, and a thick mat of dried grass under the deck strangles airflow and ruins the cut quality.
- Isolate the power as described above and tip the mower onto its side.
- Scrape the underside of the deck with a plastic scraper or stiff brush to remove caked-on grass. Avoid a pressure washer on petrol models, as water can force its way into the engine and bearings.
- Wipe down the top of the machine, the wheels, and the grass collector. A clean collector lets air flow through so the box fills properly.
- Check the wheels and height-adjuster for trapped debris, and make sure the mower is completely dry before storing it.
On corded and cordless mowers, keep the motor vents free of clippings so the machine does not overheat. A quick brush-down each time you finish is far easier than tackling a season’s worth of baked-on grass.
Step 2: Sharpen or replace the blade
A sharp blade is the difference between a clean, healthy cut and a torn, brown lawn. As a rule of thumb, sharpen the blade every 20 to 25 hours of mowing, or at least once a season for an average UK garden. If the lawn tips look frayed or whitish a day or two after cutting, the blade is overdue.
- With the power isolated and the mower tipped over, mark the underside of the blade with a dab of paint or a marker so you refit it the right way round.
- Undo the central blade bolt with a socket or spanner, holding the blade steady with a gloved hand or a block of wood.
- Clamp the blade in a vice and run a flat file along the existing bevel, working in one direction only. Keep to the original angle (usually around 30 degrees) and aim for an edge about as sharp as a butter knife – not a razor, which would chip.
- Sharpen each end equally so the blade stays balanced. You can check balance by resting the centre hole on a nail; if one end drops, file a little more off that side.
- Refit the blade the correct way up and tighten the bolt firmly.
If the blade is cracked, badly bent, or worn so thin that the metal is paper-like at the edge, replace it rather than sharpen it. Replacement blades are inexpensive and model-specific, so quote your mower’s make and model when ordering.
Step 3: Check and change the oil (petrol mowers)
Four-stroke petrol engines need clean oil to survive. Check the level before every few uses with the dipstick, topping up with the correct grade – most UK mowers use SAE 30 in summer or 10W-30 as an all-season alternative. Change the oil after the first five hours on a brand-new machine, then roughly every 25 hours or once a season.
- Run the engine for a minute so the oil warms and flows freely, then isolate the power.
- Either drain the oil from the drain plug into a tray, or use a siphon or oil extractor through the dipstick tube – often the cleanest option on a mower.
- Refill slowly with the correct quantity for your engine, checking the dipstick as you go. Do not overfill, as too much oil is as harmful as too little.
- Wipe up any spills and take the old oil to your local recycling centre – never pour it down a drain.
Two-stroke engines, found on some older mowers and many strimmers, mix oil with the petrol instead and do not have a separate oil reservoir; check your handbook for the correct fuel-to-oil ratio.
Step 4: Look after the spark plug (petrol mowers)
The spark plug ignites the fuel, and a tired plug is a common cause of hard starting and rough running. Inspect it once a season.
- Pull off the plug cap and unscrew the plug with a spark-plug spanner.
- Examine the tip. A healthy plug has a light tan or grey colour. If it is black, sooty or oily, the engine is running poorly – clean or, better, replace the plug.
- Fit a new plug if in doubt; they cost only a few pounds. Tighten only until you feel resistance plus a quarter turn – over-tightening can shear the plug and damage the thread.
Refit the cap firmly so it does not vibrate loose in use.
Step 5: Service the air filter (petrol mowers)
The air filter stops dust and grass from reaching the engine. A clogged filter starves the engine of air, causing weak, smoky running and poor starting. Check it every few uses during the cutting season.
- Foam filters can be washed in warm soapy water, dried completely, and lightly oiled before refitting.
- Paper filters should be tapped clean of loose dust but replaced once a year, as they cannot be washed.
Never run the engine without the filter in place, even briefly, as unfiltered grit causes rapid internal wear.
Step 6: Manage the fuel
Stale petrol is one of the biggest causes of spring starting trouble. Modern petrol containing ethanol can absorb moisture and start to degrade in as little as a month or two. To avoid problems:
- Buy fuel in small quantities so it is used while fresh.
- Add a fuel stabiliser if you need to store petrol over winter.
- Run the tank nearly dry at the end of the season, or drain it, so no stale fuel sits in the carburettor over the winter months.
Maintaining cordless and corded electric mowers
Battery and mains-electric mowers are wonderfully low-maintenance – there is no oil, spark plug, air filter, or fuel to worry about – but they are not maintenance-free.
Cordless battery mowers
- Keep the battery charged to a sensible level and store it indoors, somewhere cool and dry. Never leave a lithium battery flat for months or sitting in a freezing shed.
- Keep the battery contacts and the cooling vents clean and free of clippings.
- Charge the battery fully before the first cut of the season, and top it up every couple of months over winter to keep it healthy.
Major brands such as EGO, Makita and Bosch all make excellent cordless mowers; our best cordless lawnmower and best robot lawn mowers guides cover the leading options.
Corded electric mowers
- Inspect the cable before every use for cuts, nicks, or exposed wires, and replace a damaged cable straight away – never tape it up.
- Always use an RCD (residual current device) at the socket for safety.
- Keep the motor vents clear and store the mower somewhere dry to protect the windings.
For both types, the blade still needs sharpening just as on a petrol mower, so do not skip Step 2.
A year-round maintenance schedule for the UK
The British growing season runs roughly from March to October, with the heaviest cutting between April and September. Tailoring your maintenance to that rhythm keeps the machine ready when you need it.
| Season | What to do |
| Spring (Mar–Apr) | Full pre-season service: change the oil, fit a fresh spark plug and air filter, sharpen the blade, charge batteries fully, and check the fuel is fresh. Test-start before the grass takes off. |
| Summer (May–Aug) | Clean after every cut, check the oil level regularly, keep the blade sharp, and brush clippings from vents and the collector. |
| Autumn (Sep–Oct) | Raise the cutting height as growth slows, give a final clean, and begin running down the fuel as the season ends. |
| Winter (Nov–Feb) | Store properly: empty or stabilise the fuel, clean the deck, remove and store batteries indoors, and keep the machine dry and covered. |
Winterising and storing your mower
How you put the mower away in autumn largely determines whether it starts in spring. Give it a thorough clean, sharpen the blade so it is ready to go, and deal with the fuel as described above. Wipe a light film of oil over bare metal under the deck to discourage rust, take cordless batteries indoors, and cover the machine or store it in a dry shed off the bare floor. A few minutes in November saves a great deal of frustration in March.
Common problems and quick fixes
The mower will not start
On a petrol model, the usual culprits are stale fuel, a fouled spark plug, or a clogged air filter – work through those three first. On a cordless mower, check the battery is charged and properly seated; on a corded model, check the cable, plug, and RCD.
The engine runs but cuts out
This often points to a dirty air filter, a partly blocked fuel line, or a deck packed with wet grass overloading the motor. Clean the underside and the filter before anything else.
The cut looks ragged or uneven
A blunt blade is the most likely cause, followed by an uneven cutting height or a build-up of grass under the deck. Sharpen the blade and clear the deck.
White or blue smoke
Usually means oil has reached somewhere it should not be – often from overfilling or from tipping the mower the wrong way. Check the oil level and let any excess burn off before worrying further.
When to call a professional
Most maintenance is well within the reach of a confident DIY gardener, but some jobs are best left to a dealer or repair shop. Internal engine work, carburettor rebuilds, starter-cord replacement, and any electrical fault on a battery or mains mower are worth handing over to someone with the right tools. A full professional service every couple of years is a sensible investment for an expensive petrol mower, and many local dealers offer a winter service at a quieter time of year.
Frequently asked questions
How often should I sharpen my mower blade?
Around every 20 to 25 hours of use, or at least once a season for a typical garden. Sharpen sooner if the grass tips look torn or brown after cutting.
What oil does my petrol lawnmower need?
Most four-stroke mowers use SAE 30 in summer, or 10W-30 as an all-season alternative. Always check your handbook, as a few engines specify a different grade.
Can I jet-wash my lawnmower?
It is best avoided on petrol mowers, as water can reach the engine and bearings. Use a scraper and brush instead. Cordless and corded mowers should also be cleaned dry, keeping water away from the motor and battery contacts.
Do electric mowers need any maintenance?
Yes – less than petrol, but the blade still needs sharpening, the deck still needs cleaning, and batteries and cables need looking after. The good news is there is no oil, fuel, or spark plug to service.
Final thoughts
Looking after a lawnmower is one of the easiest wins in the garden. A quick clean after every cut, a sharp blade, fresh oil and a fouled-plug check once a season, and sensible winter storage will keep almost any mower running sweetly for many years. Build these habits in and you will spend far less time fighting a reluctant machine and far more time enjoying a healthy, well-cut lawn. For more practical advice, take a look at our companion guides on how to choose a lawnmower and our best petrol, best cordless, and best electric lawnmower reviews.
