Lawn mower winter storage checklist — UK guide

When to do it (October-November in the UK)

The right time is after the last cut of the year — usually late October to mid-November in southern England, late September to October in Scotland. Stop mowing once grass growth slows below about 1cm per week.

Don't store with grass clippings in the deck or bag. Wet clippings rot and corrode the blade and deck through the winter. The first task in any winter prep is a deep clean.

Don't put it off. By December, frost reaches the inside of the carb on a stored petrol mower and any moisture in the fuel system starts rusting metal parts. The 30 minutes you spend in November saves the cost of a service in March.

Petrol mower checklist (the most failure-prone)

1. Drain or stabilise the fuel. Two options:

Option A — Drain: run the engine until it stalls from fuel starvation, then drain any remaining petrol from the tank into a metal container. Discard the old fuel responsibly. The carb is now dry and won't varnish.

Option B — Stabilise: add fuel stabiliser (Briggs & Stratton, Stihl, or generic — £6, treats 20+ tanks) to the last fill of the season. Run the engine for 5 minutes to circulate stabilised fuel through the carb. Stabilised petrol stays viable for 12 months instead of 4.

2. Change the engine oil. Fresh oil contains corrosion inhibitors; used oil is acidic and pits internal engine surfaces over winter. Honda spec: 10W-30 SAE. Mountfield/Stiga: 10W-30 or 10W-40. Capacity is typically 0.6L. Drain the warm oil after a final run, refill, run briefly, check level.

3. Remove and clean the spark plug. Apply a single drop of oil into the cylinder via the plug hole; pull the rope twice to coat the cylinder walls. Replace the plug fingers-tight (don't fully torque — the cylinder is now coated and the engine shouldn't be cranked).

4. Clean the deck and underside. Scrape grass clippings from the underdeck; rinse with a hose; dry thoroughly. Wet grass left on metal corrodes through winter.

5. Sharpen the blade or schedule it. End-of-season sharpening means a clean start in spring. £20 at a dealer or 30 minutes DIY.

6. Store somewhere dry. A shed, garage, or covered porch is fine. Never under an outdoor tarpaulin — condensation under the tarp causes rust. If you have to leave it outside, leave the tarp loose enough for air circulation.

Cordless mower checklist

1. Charge the battery to 50%, not 100% or 0%. Lithium-ion batteries store best at half charge — full or empty accelerates degradation. Check the LED indicator and charge or discharge to roughly half.

2. Remove the battery from the mower. Store the battery indoors at room temperature. A cold garage drops battery temperature below 0°C, which permanently reduces capacity. The mower itself can stay in the shed; the battery comes inside.

3. Clean the deck and underside as for petrol. Cordless mowers have the same grass-and-water corrosion vulnerability.

4. Sharpen or schedule a sharpen. Same logic as petrol.

5. Don't leave the battery on the charger continuously. Trickle-charging at 100% degrades the cells. Charge to 50%, remove from charger, store cool.

6. Note the manufacture date or first-use date. Lithium batteries lose capacity over time regardless of use. Tracking the date helps you predict when replacement is due (typically year 5–7 for EGO/Bosch/Stihl batteries).

Electric corded mower checklist

1. Inspect the cable. Look for cuts, abrasion, taped repairs, and exposed copper. Replace any damaged cable before storage — a damaged cable left over winter is fine; a damaged cable used in spring is a shock hazard.

2. Clean the deck and underside.

3. Coil the cable loosely and store with the mower. Tight coils cause cable damage; loose coils don't.

4. Sharpen the blade.

5. Store dry. Corded mowers are simpler to overwinter than petrol or cordless — no fuel, no battery — but the cable and motor are still vulnerable to moisture. A dry shed or garage is fine.

Robotic mower checklist (different rules)

1. Bring the mower indoors. Robotic mowers are not designed for sustained subzero temperatures — the lithium battery and the wheel motors both suffer. Lift the mower from the dock and store indoors at room temperature.

2. Charge to 50% before storage. Same lithium-ion logic as cordless mowers.

3. The dock can stay outside but the transformer should come in. The dock itself is rated for outdoor weather; the transformer (the brick on the mains lead) is not. Disconnect the transformer at both ends and bring it indoors.

4. Disconnect the boundary wire from the dock. This protects the dock electronics from any voltage spikes from frost-induced wire shifts.

5. Clean the chassis and blade disc. Wipe down with a damp cloth; remove any grass debris. Don't pressure-wash.

6. Update the firmware before storage. A current-firmware mower starts cleanly in spring; a year-old firmware version may have known bugs that have been fixed. Husqvarna Connect, Worx Landroid, and Bosch Indego apps all manage this.

Where to store: shed vs garage vs outside

Garage (best): dry, temperature-stable, secure. Even an unheated garage stays above 5°C and below 25°C — within the safe range for batteries and engines.

Shed (good): dry and ventilated is the requirement. A leaky shed with damp floor is worse than the garage but better than under a tarp. If your shed has condensation issues, raise the mower onto a wooden pallet to keep it off the floor.

Conservatory or porch (acceptable): dry and warm. Sometimes the only option for flat-dwellers without a garage. Be aware of fumes from any residual fuel — petrol mowers shouldn't be stored in living spaces with closed doors.

Outside under tarp (worst): condensation under the tarp causes rust on metal parts. If unavoidable, use a vented mower cover (Honda and Stihl both sell these) instead of a generic tarp.

Common mistakes that ruin mowers over winter

Leaving fuel in the tank without stabiliser. Stale petrol degrades into varnish that blocks carb passages — the cause of 50% of all spring no-start problems. Either drain or stabilise.

Storing the battery on the charger continuously. Trickle-charging at 100% degrades lithium cells. Charge to 50% and remove from charger.

Storing in a damp shed without raising the mower. Condensation pools on the floor; metal parts in contact rust through. Use a wooden pallet or shelving.

Forgetting to disconnect mower from electric. Some shed installations leave the mower plugged into a switched socket — a power surge over winter can damage the motor. Unplug.

Mice and rats. A petrol mower with residual fuel in the tank attracts rodents; they chew wiring and nest in the air filter housing. A few mothballs around the mower prevents this.

Storing with a dirty deck. Grass and soil clinging to the underdeck holds moisture and corrodes metal through the winter. Clean before storage every time.

Spring restart — what to check before first cut

Petrol: connect spark plug, fill with fresh petrol, prime the carb 3 times, pull the rope. Should fire on first or second pull. If not, refer to our SP46 troubleshooting article — almost always varnished carb or stale fuel from incomplete winter prep.

Cordless: charge battery to full, install in mower, run for 5 minutes to verify motor and cutting deck are fine. Cordless mowers almost never have spring problems if stored correctly.

Electric corded: inspect cable for damage incurred during storage (mice can chew). Plug in, check the RCD trips correctly, and test cut.

Robotic: replace transformer, reconnect to dock, charge to full. Run a perimeter test (most apps offer this) before the first full cut. If 'No loop signal' appears, see the boundary wire repair article — winter frost can shift soil and break buried wires.

Sharpen the blade if you didn't at end of season. Final step before mowing season.