How to Store a Lawn Mower Over Winter (Petrol, Cordless and Corded)

Half the mowers that refuse to start in April were put away badly in October. Storing a lawn mower over winter comes down to five things: clean it, sort out the fuel or the battery, protect the underside from rust, disconnect anything that can start the engine, and keep it somewhere dry and frost free. An hour of work in autumn saves a frustrating morning in spring.

Start with a proper clean

Grass left on the deck is the single biggest cause of winter damage. Wet clippings hold moisture against bare metal for months, and by March you can be looking at rust, a seized height adjuster and a blade bolt that will not shift.

Before you do anything else, make the machine safe. On a petrol mower, pull the spark plug cap off. On a cordless, take the battery out. On a corded electric, unplug it at the wall. Only then tip it up or reach under the deck.

1. Scrape the underside of the deck with a plastic scraper or a stiff putty knife. Compacted grass comes off far easier if you soak it for a few minutes first.
2. Brush the cooling fins, the air intake and the area around the engine on a petrol mower. Trapped debris there causes overheating next season.
3. Wipe the deck dry, then give the bare metal a light spray of maintenance oil or a wipe with an oily rag.
4. Empty and rinse the grass box, and let it dry completely before it goes back on.

Avoid blasting the machine with a pressure washer. It forces water into bearings and cable ends. A bucket, a brush and a hose on a gentle setting is plenty.

Petrol mowers: decide what to do about the fuel

Modern UK petrol contains ethanol, and ethanol is the reason so many mowers will not start after a winter. It attracts moisture, separates out in the tank and leaves gummy deposits in the carburettor jets. You have two sensible options.

Option one: run it dry

Run the mower on the lawn until the tank is empty and the engine stops on its own. Any fuel left in the tank or float bowl should be drained. This is the most reliable approach if the mower will sit untouched from November to March, and it is the one most small engine repairers recommend.

Option two: fill it and stabilise it

Add a fuel stabiliser at the dose on the bottle, top the tank up to around ninety percent full, then run the engine for five minutes so the treated fuel reaches the carburettor. A nearly full tank leaves less air space for condensation. This suits you if you might still want the mower for a dry December tidy up.

What you should not do is leave the tank half full of untreated petrol. That is the worst of both worlds.

Change the oil before storage, not after

Used engine oil carries combustion acids and moisture. Left in the sump all winter, it slowly attacks the internals. Draining it while the engine is still warm from the last cut takes fifteen minutes and means the mower starts the season on clean oil. While you are there, pull the spark plug and fit a new one if the electrode looks heavily carboned, and clean or replace the air filter.

Cordless mowers: it is all about the battery

Lithium ion packs hate two things in storage, sitting fully flat and sitting in the cold. Take the battery off the mower and store it separately, indoors.

• Aim for roughly forty to sixty percent charge, not full and definitely not empty. Most packs with a fuel gauge will show two bars out of four or five.
• Store somewhere between about ten and twenty degrees. A cupboard in the house or a heated utility room beats an unheated garage or a garden shed.
• Check it once in midwinter. If it has dropped to one bar, give it a short charge back up to half.
• Keep the terminals clean and dry, and put the protective cap on if the pack came with one.

A shed that swings between minus five and plus ten all winter is what kills capacity. The mower itself can live out there quite happily. The battery should not.

Corded electric mowers

Less to think about, but the cable is the weak point. Coil it loosely rather than winding it tight around the handle, check the full length for nicks and crushed sections, and inspect the plug for scorching or loose pins. Store it off the floor so a damp concrete slab is not sitting against the insulation for months.

Deal with the blade now

Autumn is the ideal time to remove and sharpen the blade, because a seized bolt is far easier to argue with than it is in May with the grass already ankle deep. Take it off, sharpen or replace it, wipe it with oil and refit it.

Where to store it

The ideal spot is dry, ventilated, out of direct frost and off bare earth or damp concrete. A scrap of plywood or a couple of paving slabs under the wheels stops moisture wicking up into the deck.

If the mower has to live outside under a cover, use a breathable one rather than a plastic sheet, which traps condensation underneath and rusts the machine faster than leaving it uncovered. Fold the handle down if the design allows, but check the cables are not being pinched in the process.

Never store a petrol mower with fuel in it next to a boiler, a wood burner or anything with a pilot light. Petrol vapour is heavier than air and travels along the floor.

Waking it up in spring

Fit fresh fuel or the charged battery, reconnect the spark plug cap, check the oil level, make sure the blade bolt is properly tight, and test the controls before you start it. If a petrol mower still will not fire after a few pulls, the carburettor bowl is the usual suspect rather than the plug.