The verdict is in from gardeners, environmentalists, and scientists: Don’t bag your grass clippings. Let them mulch your yard. Your lawn and the environment will both be happier for it.
In the not-too-distant past, the standard advice was the opposite. We thought bagging was better and believed grass clippings contributed to thatch buildup. We also preferred the look of a lawn without the ragged bits of mown grass.
Some research and a bit of technology overcame both of those objections.
Turfgrass researchers found that trimmed lawn clippings do not cause thatch. The invention of a new class of mowing blades — mulching blades — let mowers chop the grass blades into finer pieces that are harder to see and decompose more quickly.
So today the norm is “grasscycling” — returning the cut blades of grass right back to the soil.
“Overall, it is better to mulch because the nutrients remain in the soil,” said Teris Pantazes, CEO of the Baltimore-based handyman community site, EFynch.com.
“Avoiding the bagging of cuttings will help the environment – avoiding the need for this waste material to enter landfills,” said Thomas O’Rourke, of the garden advice site DeckingHero.com.
Changing standard favors mulching
“I would say that the standard has changed over time as people have begun to recognize the nutritional benefit of mulch on their lawns,” O’Rourke said.
“Bagging is definitely neater because there will be no clumps of grass left over,” said Luke Truetken, owner of Luke’s Landscape & Maintenance of McKinney, Texas. “However, it’s not necessarily the best thing. Mulching allows the clippings to revitalize the lawn with nutrients as they decay. If done correctly, it also doesn’t reduce the neat appearance, either.“
5 benefits of lawn mulching
There are at least five benefits to mulching your grass clippings.
1. Grass clippings are a natural fertilizer.
By mulching, you reduce your lawn’s fertilizer needs. “Mulching re-introduces essential minerals to your lawn that would otherwise be lost,” O’Rourke said. “For example, nitrogen, phosphorus and potassium are all preserved by utilizing the mulch, reducing the need for artificial fertilizers to keep your lawn looking healthy.”
Leaving the mulch in your lawn returns several pounds of nutrients to your lawn each season.[table id=16 /]
That’s “a considerable amount when typical recommendations suggest 2 to 5 pounds of actual nitrogen per 1,000 square feet of lawn annually,” notes Oregon State University’s Extension Service. Lawn clipping mulch allows you to skip the time and expense of a nitrogen fertilizer cycle while still maintaining a healthy lawn.
2. Clippings hydrate.
Mulching lawn clippings “helps lawns stay hydrated in high-heat and drought conditions,” said Cassy Aoyagi, president and co-owner of FormLA Landscaping of Los Angeles.
“Grass is 80 percent water, so in essence, you’re watering your lawn a bit by leaving them there,” said Allen Michael, editor of SawHub.com, a site for do-it-yourselfers.
3. Mulching reduces landfill use.
Mulching your yard clippings reduces dump fees and keeps yard waste out of already-strained landfills. “Bagging is not so environmentally friendly unless you have a compost pile, which most people do not have,” Truetken said. “Some cities collect yard waste for composting, but usually it just ends up in the landfill.”
“You’re reducing landfill waste by not bagging, and cutting back on plastic, since the bag will inevitably be plastic,” Michael said.
The mulching of yard trimmings has been a success story for landfills. A 2018 report from the U.S. Environmental Protection Agency, shows Americans generate about 34.7 million tons of yard trimmings per year. That’s 69.4 trillion pounds. But just 10.8 million tons end up in landfills. That’s down from 27 million tons in 1980.
In part, that’s because the norm has changed, and people either mulch or compost their trimmings from grass plants. Also, state governments have taken action to keep yard trimmings out of their landfills. According to data from The Composting Council, 25 states have regulations limiting or banning yard clippings in landfills. The states are: Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Iowa, Maryland, Massachusetts, Michigan, Minnesota, Missouri, Nebraska, North Carolina, Ohio, Pennsylvania, South Carolina, South Dakota, Vermont, New York and Wisconsin.
4. Mulching is less work.
“Bagging is additional work as you need to stop frequently and empty the bag,” Truetken said.
5. Mulch is a natural weed killer.
Weed control is important. Your layer of lawn clipping mulch will be less than an inch thick, but regular mowing and mulching provide a barrier to weed seeds, preventing them from taking root.
When you should bag your lawn trimmings
The experts allow for some exceptions to the general “don’t bag your clippings” rule.
For one, says O’Rourke, “If you haven’t cut your lawn in a while, don’t be afraid to bag some of your clippings. Leaving too much excess grass on your lawn can block sunlight leading to patchiness and discoloration.”
Also, a new lawn grown from seed may be too delicate to withstand a coating of trimmings.
The University of Minnesota Extension service suggests mulching is not appropriate if you’re giving your lawn a big trim. In no case should you ever remove more than one-third of the length of your grass in any single mow. But if you’re following the “one-third rule” and the cut grass is still long, remove it.
“As a general rule, grass clippings of an inch or less in length can be left on your lawn where they will filter down to the soil surface and decompose quickly,” according to the Minnesota Extension Service. “Remove longer clippings because they can shade or smother grass beneath, causing lawn damage.”
“Shorter grass bits will break into the soil more easily, unlike longer ones,” said Pol Bishop of Fantastic Gardeners, a London-based lawn service company. “So next time you mow your lawn you will know if you should keep the grass clippings on or not.”
There is another exception. Go ahead and bag the clippings if your lawn has a thick layer of thatch — a half-inch or more. According to the Missouri Extension Service, “A layer more than 1/2 inch thick will prevent clippings from coming into contact with soil microorganisms,” preventing the clippings from breaking down.
Finally, some pet owners like to remove lawn clippings to prevent pooch paws from tracking them indoors.
How to compost lawn clippings
Reardless of your reason, if you do decide to remove the trimmings from your lawn, you can use grass clippings as part of a compost pile. The heat of the composting process will convert into fertile soil for your garden beds, raised beds and vegetable garden plots.
Composting has become a common practice for lawn clippings. Americans have come to make mulch ado about composting. According to the EPA, “Composting was negligible in 1980, and it rose to 23.4 million tons in 2015.”
“Grass falls into the ‘green’ portion of what is necessary for successful composting, said Michael, whose site includes a compost bin guide. “Along with water and some ‘browns,’ such as paper, cardboard, sawdust, or leave clippings, you have the makings for successful composted soil.” Dry leaves, wood, and straw are other “browns” that will balance out your grass clippings.
Since fresh grass clippings are about 80 percent water, you may not need to water the compost pile when blending in the clippings. Dry grass may require sprinkling some water on the compost pile.
Missouri’s extension service recommends a 1:1 to 2:1 ratio of brown to green. Be sure the clippings are pesticide free before adding the organic matter to the compost pile.
Mulching equipment: Mowers and blades
If you or your lawn care pro mow frequently with a sharp blade, a regular lawn mower with a standard “2 in 1” blade is sufficient for most mulching needs. The mulch may clump a bit and create larger pieces, but for ordinary lawns, that’s fine.
But if you are looking for finer, clump-free mulch, consider a mulching blade kit or a mulching motor.
Mulching blades are sometimes called “3-in-1” blades since they have an extra duty. They not only discharge to the ground or to the side, but they also mulch.
They are designed with multiple cutting edges and aerodynamic shapes that keep grass suspended under the deck of the lawn mower. While suspended, each blade of grass gets chopped several times by the mower blade. The result is mulch in such tiny pieces that it is nearly invisible.
Mulching blade kits are available for as little as $20, but shop carefully, as they are often brand-specific and not universal. As always, if you are planning to put your hands under a mower, disconnect the spark plug or electric cord to prevent accidental starting.
Dedicated mulching mowers tend to have larger engines better able to handle the multiple cuts, and “decks” (the metal awning over the blade) designed to facilitate the process
A few newer mowers even allow you to control the level of mulching so that some of the grass returns to the lawn, and some is diverted to the bagger.
No matter which blade you have, keep it sharp. Experts advise sharpening the mower blade at least yearly, and more often if your lawn is big or you mow frequently. The rule of thumb is to sharpen the blade once for every 25 hours of use.
“Keeping the blade sharp will also improve mulching, as well as helping the grass stay healthier,” Truetken said.