Image 1. Homeowner front lawn that was used for the study.
Maintaining a thriving, beautiful lawn often comes down to more than just fertilizing and watering. How you manage your grass clippings, whether you mulch them back into the lawn or bag and collect them, may have a surprising impact on your lawn’s health, appearance, and nutrient cycles. Drawing on recent findings, including an in-depth 8-month study with 80 soil tests (five replications per treatment per month), here’s what you should know to make the best decision for your yard.
Image 2. The Toro mower that we used for the study had a lever to convert between mulching and bagging which made this work much easier.
How Mulching Works—and Its Benefits
Mulching means leaving finely-chopped grass clippings on your lawn after mowing. These clippings are high in essential nutrients, especially when they are young and freshly cut. When mulched into the lawn, they act like a “candy bar” for soil microbes, offering:
- Quick decomposition: Small, nitrogen-rich clippings break down quickly, usually within a few weeks.
- Nutrient recycling: Essential lawn nutrients like nitrogen, potassium, and phosphorus are returned to the soil, often reducing the need for supplemental fertilizers.
- Improved soil health: Microbial activity is boosted, benefiting root development and soil structure.
- Sustainability: Mulching keeps organic matter on your property and out of landfills, helping the environment.
Image 3. Example of clipping size when mowing frequently and following the 1/3 leaf surface rule. Learn more about the 1/3 leaf surface rule here.
When Mulching Works Best
- When frequently mowing (2–3 times per week during peak growth periods): This keeps clippings small and easy to decompose.
- When lawn is healthy and well-fertilized: Soil microorganisms will quickly process the clippings when nutrients such as nitrogen and sulfur are not limiting factors.
- When the grass is dry and a manageable length: Mulching works best when you’re not cutting away large amounts at a time and when the grass is dry so that it doesn’t clump together.
Challenging Scenarios for Mulching
While mulching is ideal in most scenarios, improper practices can cause thatch buildup, clumping, and aesthetic issues:
- Long, woody clippings (from infrequent mowing): These break down more slowly due to a higher carbon-to-nitrogen ratio, potentially contributing to thatch. Consider bagging to avoid a mess. Alternatively or additionally, you could increase your mowing height.
- Clumping on wet or overgrown lawns: These clumps can smother living turf beneath, causing yellowing or bare spots. Allow the turf to dry if possible and rake up and remove any clippings left behind.
Image 4. Longer, stemmy clippings from not following the 1/3 leaf surface rule. These will break down slowly and may lead to thatch buildup.
The Case for Bagging Grass Clippings
Bagging involves collecting clippings using your mower’s bagging attachment. Some scenarios make bagging preferable:
- When grass is wet or overgrown: Prevents clumps and possible lawn suffocation. In the case of a lawn being overgrown it minimizes the chance of thatch buildup.
- After weed or seed flushes: Limits the spread of invasive species, especially if you compost clippings hot enough to kill seeds. Weeds that ‘creep’ by stolons or runners should not be added to the compost pile as it may aid in their spread.
- When managing lawn diseases or pests: Removes potentially infected clippings and helps control spread.
- When personal preference dictates the utmost tidiness: Keeps clippings out of your home and off of your hardscapes; ideal for those with children or pets who are in and out frequently, or for those who prefer a pristine look.
- During seasonal transitions: Bagging may be beneficial during spring and fall when certain grass types release seeds or during periods of excessive rain. It can also be beneficial if you are lowering your height of cut as seasons transition or just before overseeding your lawn.
Making Use of Bagged Clippings
Bagged clippings don’t have to go to waste:
- Compost: Add bagged clippings to your compost pile for future garden or landscape use.
- Garden mulch: Use as a weed suppressant between rows or around the property perimeter.
- On-site recycling: Always strive to keep nutrients within your property rather than sending clippings to a landfill or otherwise offsite.
Image 5. Adding grass clippings to compost in a future garden bed.
Image 6. Dumping clipping to later be used as a weed-suppressing mulch between the covered rows in a garden.
What Does the Science Say about Mulching vs. Bagging?
A unique aspect of the recent study was its data driven approach. After splitting a homeowner’s yard and comparing mulched versus bagged sections over a full season this is what we learned:
- No visual difference was observed in turf health or appearance.
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Soil nutrient differences were minor but notable:
- In the spring (peak uptake period), phosphorus and potassium levels were higher in the mulched sections. This is likely because both nutrients can be leached or mineralized from clippings and recycled into the topsoil, especially during the growing season.
- Iron and manganese levels were significantly lower when clippings were bagged, however the levels still remained in the optimal range in this lawn.
- Overall, none of the approaches caused harm or major loss in soil fertility over the season.
- Thatch buildup was not notable with mulching. This was linked to frequent mowing and therefore low clipping load.
Figure 1. Phosphorus and potassium levels monthly, April through October between mulched and bagged treatments.
Figure 2. Calcium, Iron, and Manganese differences from beginning to end of study. Expressed as percent change.
Figure 3. End of season soil test comparison between bagged and mulched treatments. This figure represents the averages of five replications of each treatment.
When Should You Mulch vs. Bag?
Here’s a quick reference:
Takeaway: Tailor Your Approach
There’s no one-size-fits-all answer. Many homeowners will benefit from mulching most of the time, with occasional bagging during unique situations. The key is to balance aesthetics, lawn health, and ecological responsibility.
Whenever possible, keep all clippings and nutrients on your property, whether mulching directly or bagging and using them elsewhere in your landscape. Thoughtful management leads to a healthier, more sustainable lawn.
Need to know if your soil is getting the nutrients it needs? Try a professional soil test and take the guesswork out of your lawn care.
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