What is a Mulching Lawn Mower and How Does It Work?

senior man on a riding lawn mower mulching up leaves while cutting the grass

Are you perplexed by the many different lawn mowers on the market? Mulching lawn mowers are a popular option for homeowners today because they offer multiple ways to get rid of your grass clippings. 

What is a mulching lawn mower?

A mulching mower is a machine where the blade and mowing deck are designed to chop the grass multiple times before the cut grass goes back into the lawn. Side discharge mowers direct the grass to the side, and using a bag attachment directs the grass clippings into the bag. 

Among these three types of mowers, only the mulching mower leaves you with finely cut grass cuttings, which provide fertilizer and shade for the soil. You may hear this kind of mowing called “mulch mowing.”

How does a mulching mower work?

Mulching mowers aren’t different from other mowers in most ways. In all lawn mowers (push mowers, ride-on, etc.), you need lift so the grass stays vertical while the mower blade cuts. 

Mulching mowers not only create a stream of air that directs the grass up into the mower blades, but once the grass is cut, the clippings hit the blade multiple times before they go back onto the lawn. This is in contrast to other mowers which direct the clippings out the side or into a bag.

This is by design, of course. Mulching blades use curved edges to generate this extra cutting action and generally have more surface area devoted to cutting.

Mulching blades are sometimes called “all purpose” or “3-in-1” blades because you can use them to mulch, bag, or side discharge. Standard blades are called 2-in-1 blades because you can use them to either bag or side discharge the grass.

Can I use my current mower to recycle my grass clippings?

Yes. Contact your local lawn mower retailer (or your mower manufacturer) to ask if you need a conversion kit. These mulching kits may include a plate (AKA mulching plug) to close your discharge opening (or bag opening) and a new blade. Or, you may only need a new blade.

Both push and ride-on mowers can recycle grass clippings back into the lawn. Close your discharge chute or remove the bag and voilà. However, a mulching mower blade does a better job because the pieces are smaller and will break down more quickly in the lawn.

How to use a mulching mower

In short, use it just as you would any other mower. Here are a few lawn care tips to make sure your mulching mowing sessions are a success:

  • Don’t mow when it’s wet. The mower might not be able to cut the grass blades as finely due to the extra weight and tendency to clump. Also, the underside of your lawn mower will be covered in wet grass.
  • Mow often. Follow the golden rule of mowing: Remove no more than one-third of the grass blade per mow. 
  • Mow at the correct height. Believe it or not, this simple advice makes a big difference in your lawn. Each grass type performs best when cut at a certain height. (There are many soil and grass scientists who devote lots of time and energy at grass test plots to figure this out.) 

The seasons also can make a difference in your mowing height. Some advise that you should mow a half inch taller during the hottest part of the year and mow slightly shorter for the first and last cuts of the season. (Where it snows, it may be advisable to mow as low as possible on the last mow to prevent snow mold.) 

Ask your local Cooperative Extension office for the best seasonal advice.

  • Consider your lawn density. A dense lawn may put extra strain on your mower. When you’re buying a lawn mower, buy one that has sufficient power for your needs. Don’t skimp in this area — you’ll regret it.
  • Maintain a sharp blade. A sharp mower blade is a must. A sharp mower blade gives you a clean cut instead of a torn one, which can invite disease into your lawn. Use a file, a hand grinder, a bench grinder, or a sharpening stone attachment on your cordless drill to sharpen the blade.
illustration depicting the grass cut with a sharp blade vs a dull blade

How often should you sharpen your mower blade? It depends on the type of grass you have, how often you mow, and the density of your lawn. Here’s an easy test: If you look at the tip of the grass blade and it looks torn instead of cleanly cut, it’s time. If you have a dense lawn with stiff-bladed grass like Zoysia, you may need to sharpen your blade as often as once per month.

  • Keep the deck clean. Hose off the clippings underneath the deck at the end of each mowing session. A buildup of gunk on the underside of the deck may prevent the clippings from circulating as well as they should.

Mulching matters

You may wonder, “So, what’s the big deal about whether I mulch grass or not?” Well, mulched clippings not only contribute to a healthy lawn but help out your local environment as well. 

Cities are jumping on the bandwagon because, for one reason, grass clippings produce a lot of waste. According to the Connecticut Department of Energy and Environmental Protection, a half acre lawn can generate “260 bags of grass clippings” in a single year — that’s more than 3 tons! 

As you can see, it’s also in their best interest to educate homeowners on the benefits of recycling their grass clippings back into the lawn and reduce the landfill waste in their city.

To sum it all up, mulching, sometimes called “grasscycling” has many benefits:

  • Saves time (no more raking fall leaves)
  • Saves money (free fertilizer, no garbage fees)
  • Helps protect the environment (no grass clippings in streams or landfills)
  • Reduces erosion (helps keep the soil in place)


1. Are there any times I should not mulch in my clippings?

Yes, there are instances when it’s best not to mulch your grass clippings back into the lawn.

When you have a fungus: If you’re trying to recover from a fungus on your grass, don’t mulch in these lawn clippings. That would only spread the disease further across your lawn.
If you have weeds that are going to seed: It’s a good idea to bag in this instance and put the clippings in your yard waste bin. You don’t want to help your weeds redistribute their seeds for next season.
If you have too many leaves on the lawn: If you have over 50% leaf coverage, you may want to bag as you mow. Too much leaf litter and grass mulched into the lawn at one time can damage the grass. Afterward, add the mulched leaves/grass mix to the compost bin, or use the mix as winter protection for your flower beds.

2. Other benefits of using a mulching mower:

No cumbersome bag to deal with on the lawn mower
No concerns about how to dispose of your grass clippings
Fertilize and mow at the same time
Avoid putting valuable nutrients and moisture into the landfill

3. Will the clippings contribute to the thatch in my lawn?

The short answer is no, cut grass clippings do not contribute to thatch in your lawn. Thatch is a layer of organic matter (living and dead) that accumulates between living, growing vegetation (grass) and the soil. 

As long as the thatch is less than about a half inch, your lawn is fine. If it gets above that level, depending on your grass type, you may want to consider dethatching or aerating (which will inevitably remove some of the thatch). (Note: Aeration is when you pull plugs from the soil to help air, water, and nutrients circulate better throughout. This helps roots grow deeper and stronger, and you have a greener, healthier lawn as a result.)

If you’d enjoy having someone else mow and fertilize your lawn (with your grass clippings or with store-bought fertilizer), contact one of our local lawn care pros. They’ll get your lawn on the path to a greener, fuller future.

Main Photo Credit: PublicDomainPictures.net

Sarah Bahr

Sarah is a writer who has previously worked in the lawn care industry. In her spare time, she likes to garden, raise chickens, and mow the grass with her battery-powered lawn mower.