How to Winterize Your Lawn Mower in 3 Steps

For most homeowners, winter’s approach means putting lawn mowers into hibernation.

“Most of the time when they’re done with that last mowing of the season, there’s a little bit of celebration,” says Kathleen Cue, Horticulture Educator with the Nebraska Extension. “The mower gets parked in the shed or garage and forgotten about until spring.”

Jelly in Your Mower’s Tank

Unfortunately, finishing that last mow isn’t the end of the work. And leaving the mower with half a tank of gas and covered in grass clippings isn’t a good idea.

“Over the winter months, the gasoline that’s in the tank can turn to jelly,” Cue says. “And that makes it really hard for lines to move that gasoline.”

Bad news for the unwary operator during that first springtime mow.

But it’s easily avoided by taking the right steps to winterize your mower. And even for a riding mower, winterization is a fairly easy process. Done right, when springtime comes again, it will crank right up for that first cut of the new year.

Winterize your most important summertime tool with these three steps, and it’ll be safely tucked in for the cold weather ahead.

Step 1: Clean Up

Clean up the mower’s “deck” — the flat cover above the mower blade.

The first thing to do is give it a good cleaning, whether you’re working with a push-behind, riding lawn mower, zero-turn or lawn tractor.

Clean and dry means you won’t find any surprises when the weather warms up again.

Manufacturer Briggs and Stratton says it’s a good idea to keep your owner’s manual handy for reference.

And, as with any maintenance, remove the lead wire from the spark plug and tape or tie it out of the way.

  • Start by removing the battery if your lawnmower has one.
  • Remove debris, clumps of grass and moisture from the mower deck, lawn mower blade and other components.
  • Clean the terminals, charge it fully and store the battery in a cool, dry place.
  • Brush off or use a garden hose to remove any build-up of leaves, grass clippings and mud.
  • If it’s a push mower, gently tip it on its side and use a putty knife, wire brush or other tool to remove debris on the blade or mower deck. Never use your hands.

“It’s always a good idea to clean out the deck of the mower,” Cue says. That bunched-up grass can also be perfect for nesting mice or increase energy use, and can hold water and lead to rust.

Electric Mowers’ Lithium-Ion Batteries Need Care

For electric mowers, Cue also recommends taking off the large plastic cover on top of the motor. This makes an excellent place for mice to nest during the cold months, leading to an overheating motor prone to stop itself, she says.

One year her electric mower wouldn’t stop overheating and shutting itself off. Taking off the cover, she found the nests. You want to minimize the number of places that can happen, she says.

The ion-lithium batteries that charge modern electric mowers need special care in winter:

  • Store the batteries inside, not on the mower. Check your manufacturer’s guidelines, but most batteries last longest when stored between 40 degrees and 80 degrees Fahrenheit.
  • Don’t store the batteries fully charged. Try to keep them at about a charge of slightly less than half-full. Many of the chargers have indicators — often in the form of light bars — displaying charge level.
  • Once they hit that level, store them in a cool dry place disconnected from the charger. Recheck and if necessary, recharge about once a month.

Step 2: Drain or Stabilize Fuel

Adding fuel stabilizer
Adding fuel stabilizer.

The next step is either draining or stabilizing your mower’s gasoline.

Cue says that many people think the mower will be fine if the gas cap stays closed and keeps fuel clean.

But that’s not the issue. It’s the gelling of the gas that’s the issue, she says. That gas will need to be treated or emptied.

As the North Carolina State University Extension recommends, consult your owner’s manual. If there’s an easy way to drain gasoline from the fuel tank, drain or siphon it.

That gas can go straight in your car’s tank or other approved gas can. And clear the excess gas by running the motor until it stops.

If there’s no easy way to empty the gas tank, the extension says, then treat it with a fuel stabilizer.

Follow instructions on the container of stabilizer, and fill it completely. A full tank means no room for air.

Run the tank for a few minutes to pull the mixture through the fuel lines and carburetor.

Cue recommends just mowing until the engine stops.

And do not skip this step.

Gasoline left in an engine’s fuel tank and carburetor degrades over time. When it interacts with air and moisture, the gas forms gels and deposits.

That can mean clogs in fuel lines and fuel filter that can wreak havoc on your fuel system.

Untreated gas shouldn’t sit for more than two months, NCSU says.

Step 3: Preventive Maintenance

Checking the spark plug
Check the spark plug, especially if the mower has been hard to start or you smell gas.

This is also a good time on your lawn care calendar to pencil in other routine lawn mower maintenance.

Give the mower a good inspection, Cue says. Is the pull cord showing wear and tear? Add replacing it to your to-do list.

This is a good time to inspect and if necessary replace your spark plug. It provides the charge to burn your gas-air mixture. If your mower has been hard to start, or you have smelled gas, the gap may need to be reset or the plug may need to be replaced. Check your owner’s manual for details.

Take out the spark plug and see if it’s still in good shape. 

A guide from the University of Georgia Extension says you can check your spark plug with a spark plug test tool or spray starter fluid in the open choke of the carburetor to see if it’s sparking.

While the plug is out, spray a small amount of light lubricating oil into the cylinder through the spark plug hole, UGA says.  Then pull the starter cord a few times to work the oil into the cylinder. It’ll stave off rust and keep all those moving parts moving. 

Time for a new spark plug? Briggs and Stratton says many small engines require a gap of 0.30 inches. Use a spark plug gauge to measure the gap. If necessary, the gauge can be used to bend the electrode to the correct spot.  When it’s right, the gauge will drag slightly as you pull it through. 

If needed, give your lawn mower an oil change by replacing the old oil and installing a new oil filter. Replace the air filters and change other fluids. Store your mower in a dry place.

But, Cue recommends waiting until spring to sharpen the mower blade. A freshly sharpened blade is freshly opened to rust, so that may be a chore to help kick-start the next mowing season.

If needed, give it an oil change by replacing the old oil and installing a new oil filter. Replace the air filters and change other fluids. Store your mower in a dry place.

As the Virginia Tech Extension says, this type of servicing isn’t at the top of most people’s to-do list. “But it is a practice that reaps large rewards next season.”

Most fluids and filters need regular changing on any gas-power equipment to optimize performance and extend engine life. Inspect any belts and replace them if needed.

Finally, it’s mower storage time. Toss a tarp over it until next spring and rest easy. You’ll be ready next spring for mowing season and you won’t be left holding the pull cord on a mower that won’t start.

All photos by Derek Lacey.

Derek Lacey

Derek Lacey

Formerly the agriculture writer for the Hendersonville Times-News, Derek Lacey’s articles have appeared in U.S. News & World Report, The Charlotte Observer, News & Observer, and The State. He has won 15 awards from the North Carolina Press Association and GateHouse Media, for pieces ranging from news features and investigative reporting to photography and multimedia projects.