How to Winterize a Lawn Mower: Gas and Cordless Checklist

To winterize a gas mower, treat fresh fuel with stabilizer and run the engine a few minutes (or empty the fuel system if your manual says so), clean the deck, check the oil, spark plug and blade, and store it somewhere dry. For a cordless mower, clean it, take out the battery, and keep the battery indoors at about 40 percent charge unless your manual says otherwise. Old fuel left in a carburetor is the usual reason a mower will not start in spring, so do that step first.

Before you start

Do this job after your last real mow, when the grass has stopped growing and the leaves are done. See rake or mulch leaves if you still have a final pass to make.

• Work outdoors or in a well-ventilated space, away from flames and sparks.
• Let the engine cool completely.
• Before touching the blade, pull the spark plug wire or remove the safety key and battery.
• Wear heavy gloves around the blade.
• Keep fuel, oil and cleaners away from children and pets.
• Have your owner’s manual handy. If it disagrees with a general guide like this one, follow the manual.

Quick comparison

Gas mower checklist

1. Deal with the fuel. Sources warn untreated fuel can begin to degrade in as little as 30 days. Add stabilizer to fresh gas at the rate on the bottle, then run the engine for a few minutes so treated fuel reaches the carburetor. Some manuals instead tell you to run the tank dry or drain it. Do whichever yours says. Claims for how long stabilizer lasts vary from about 6 months to 2 years, so go by the bottle.
2. Check your fuel type. Use the fuel your manual lists, usually E10 or less. The EPA says E15 must not be used in nonroad engines such as lawnmowers. If your pump gas is E15, replace it before storage.
3. Disconnect the spark plug wire. Tuck it away from the plug.
4. Clean the deck. Scrape off packed clippings with a plastic scraper or stiff brush, because wet clippings hold moisture against the steel. If you need to tip a walk-behind, follow your manual. Many say to keep the carburetor and air filter side up, so oil and fuel do not leak into them.
5. Check the oil. Sources disagree on whether a change is needed before storage. A common maintenance schedule is about once a year or every 50 hours. Doing it in fall means used oil is not sitting in the engine over winter, and you start spring ready to go. Take used oil to a collection site.
6. Look at the air filter and spark plug. Clean or replace the filter according to the manual. Replace a fouled or worn plug.
7. Sharpen or replace the blade. NC State notes that dull blades tear leaves, leaving ragged ends that wither. See our guide to sharpening garden tools, and keep the blade balanced when you sharpen it. Winter is also a good time to have a shop do it.
8. Wipe it down. Clean the engine’s cooling fins and shroud of grass. Lightly oil exposed metal and pivot points if the manual allows.
9. Store it dry. Pick a garage or shed, away from any furnace, water heater or other ignition source if fuel remains. A breathable cover keeps dust off.
10. Leave it alone. Do not start it midwinter for a quick run. Short cold starts can cause condensation inside the engine.

Riding mowers and electric-start batteries

Follow the same steps as above, then deal with the starter battery. Most riding mowers use a lead-acid battery, which is usually stored fully charged. Keep it on a maintainer, or take it off and store it somewhere cool and dry, charging it through the winter as the manual suggests. Check tire pressure too.

Cordless mower checklist

1. Remove the battery and safety key. Do this first, every time.
2. Clean the deck. Brush off clippings and wipe with a damp cloth. Check your manual before using any water near the motor or electronics.
3. Check the blade. Sharpen or replace it now. Use gloves, and keep the battery out of the mower.
4. Check the charge level. Consumer Reports advises that if a battery will sit for 30 days or more, bring it to about 40 percent. Check your manual for how to read your battery’s charge gauge.
5. Store the battery indoors. Most batteries do best at cool to room temperature, so a closet or utility room is better than a cold shed; your manual gives the exact range. Keep it dry and away from heaters.
6. Read the manual for midseason care. Instructions differ. Some packs need no charging all winter, one major maker advises topping up every two months and then draining back to 40 percent, and at least one says to keep a mower on its charger if storage stays above 40°F. Older mowers with fixed or lead-acid batteries may call for a full charge.
7. Warm it before charging. If a battery has been in the cold, let it reach room temperature first. Most lithium-ion packs should not be charged below freezing.

Spring restart

• Fill with fresh fuel of the right type.
• Reconnect the plug wire and fit a charged battery.
• Check oil level and tire pressure.
• Run a first mow at a higher deck setting.

Bottom line

Fuel is the step that matters most on a gas mower, and battery care is the step that matters most on a cordless one. Clean the deck, sharpen the blade, keep the machine dry, and follow your manual where it differs. A little work now saves a repair bill and a stubborn pull cord in April.

FAQ

Should I drain the gas or use stabilizer?

Either can work. Follow your manual. Stabilizer is simple and protects the carburetor, while emptying the fuel system removes the problem altogether.

Do I have to change the oil before storage?

Not always. Oil lasts longer than gas in storage, so it depends on your schedule. If it is due, fall is a convenient time.

Can I leave a cordless battery on the charger all winter?

Only if your manual says so. Most advice for removable lithium-ion packs is to store them partly charged, off the charger, indoors.

Can a mower stay outside over winter?

It is a poor idea. Moisture rusts the deck and the engine parts. If you have no shed, use a waterproof, ventilated cover and raise it off the ground.