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Close-up of fresh green grass with morning dew

Should You Bag or Mulch Your Grass Clippings? Here’s What Actually Matters

LAWN

I get this question at least once a week. A homeowner flags me down mid-mow and asks, “Hey, should I be bagging these? My neighbor says leaving clippings kills the grass.”

Your neighbor is wrong. But I get why the myth persists.

Here’s the truth, backed by actual research and about a thousand lawns I’ve mowed over the years: mulching your clippings is almost always the better choice. But there are exceptions, and knowing when to bag can save your lawn from real problems.

Let me break down what’s actually happening when those clippings hit the ground.

The Biggest Myth in Lawn Care

“Grass clippings cause thatch.”

I’ve heard this more times than I can count. It sounds logical—you’re leaving organic material on the lawn, so it must build up, right?

Wrong.

According to the University of Minnesota Extension, grass clippings are composed mostly of water and break down rapidly. They don’t accumulate into thatch. Thatch is actually made up of stems, roots, and rhizomes—the tougher parts of the grass plant that decompose slowly. The soft leaf blades you’re cutting? They’re gone within a week or two.

The confusion probably started because people saw clumps of wet grass sitting on their lawn and assumed that’s what thatch was. It’s not. Thatch is a layer that forms between the soil and the living grass, and it’s caused by grass varieties that produce a lot of lateral stems, not by your mowing habits.

So if someone tells you to bag because of thatch, you can politely tell them the research doesn’t support that.

What Happens When You Mulch

When you leave clippings on the lawn, a few things happen:

They decompose quickly. Within a couple of weeks, microorganisms in your soil break down those clippings and release the nutrients back into the ground.

Your lawn gets free fertilizer. Grass blades contain nitrogen, phosphorus, and potassium—the same nutrients you’d pay for in a bag of fertilizer. Research from the University of Missouri Extension found that recycling clippings can provide up to 25% of your lawn’s annual fertilizer needs. That’s not nothing.

You save time. No stopping to empty bags. No dragging heavy bags to the curb. No paying for yard waste pickup.

Your soil stays healthier. Those clippings feed the microbes and earthworms that keep your soil alive. Healthy soil grows healthier grass. It’s a cycle that works in your favor when you let it.

I’ve seen lawns that have been mulched for years next to lawns that bag religiously. The mulched lawns are almost always thicker and greener, assuming everything else is equal. It’s not magic—it’s just biology doing its thing.

When Bagging Actually Makes Sense

Now, I’m not going to tell you mulching is always the answer. There are real situations where bagging is the smarter move.

When you’ve let the lawn get too long. Life happens. You go on vacation, it rains for a week straight, whatever. If your grass is significantly overgrown and you’re cutting off more than a third of the blade height, those clippings are going to sit in heavy clumps on top of your lawn. Those clumps can smother the grass underneath and create dead spots. In this case, bag it—or at least rake up the clumps afterward.

When the grass is wet. Wet clippings stick together and form mats instead of filtering down to the soil. They can also clog your mower. If you have to mow when it’s wet (sometimes you do), bagging prevents the mess.

When you’re dealing with a lawn disease. This is the big one. Fungal diseases like brown patch, dollar spot, and red thread spread through spores. When you mow an infected lawn and scatter those clippings everywhere, you’re essentially spreading the disease across your entire yard. If you notice irregular brown patches, lesions on grass blades, or anything that looks like a fungal infection, bag your clippings until you’ve treated the problem. The University of Minnesota Extension specifically recommends this approach for disease management.

When you’ve just applied certain herbicides. If you recently treated your lawn with a broadleaf weed killer (like 2,4-D), those clippings may still contain residue. The Missouri Extension cautions against using fresh clippings as mulch in your garden beds after herbicide application because it can damage your plants. Bagging for a few mows after treatment is a reasonable precaution.

When you want that pristine, golf-course look. Some people just prefer the clean appearance of a freshly bagged lawn. Nothing wrong with that. It’s your yard. Just know you’re trading some long-term soil health for short-term aesthetics.

How to Mulch the Right Way

If you’re going to mulch—and again, most of the time you should—there are a few things that make it work better.

Mow regularly. This is the biggest factor. If you’re only cutting off a small amount each time, the clippings are tiny and disappear into the lawn almost immediately. The old rule of thumb is to never remove more than one-third of the grass blade at once. Stick to that, and clumping isn’t an issue.

Keep your blades sharp. A sharp mower blade cuts cleanly. A dull blade tears the grass, leaving ragged edges that turn brown and make your lawn look rough. Those torn blades also decompose slower. I sharpen my blades regularly throughout the season—it makes a visible difference.

Mow when it’s dry. Morning dew or recent rain means clumpy, matted clippings. Wait until the lawn has dried out, usually mid-morning or late afternoon.

Consider a mulching mower. Mulching mowers have specially designed blades and decks that chop clippings into finer pieces and recirculate them before dropping them. You don’t need one, but they do a better job of making clippings disappear.

The Environmental Angle

This might not be why you clicked on this article, but it’s worth mentioning: bagging your clippings creates a lot of waste.

The Missouri Extension references a study showing that in one city of 80,000 people, over 700 tons of grass clippings were collected and hauled to the landfill each week during the growing season. That’s an enormous amount of organic material that could have just stayed on the lawn and fed the soil.

Landfills don’t need your grass clippings. Your lawn does.

What I Do (And Why)

On most lawns I service, I mulch. It’s better for the lawn, faster for me, and the results speak for themselves.

But I pay attention. If I show up and the lawn got away from someone—maybe they were out of town, maybe it’s been raining—I’ll adjust. Sometimes that means raising the deck and making two passes. Sometimes that means bagging the heavy stuff and mulching the rest.

The point is, there’s no single answer that works for every lawn on every day. The best approach is to understand what’s actually happening and make the call based on conditions.

For most homeowners mowing a typical lawn on a regular schedule? Leave the clippings. Your lawn will thank you.

The Short Version

  • Mulch most of the time. It returns nutrients, saves time, and doesn’t cause thatch.
  • Bag when the grass is overgrown, wet, or diseased. Also bag after herbicide applications if you’re using clippings in gardens.
  • Mow regularly with sharp blades. This is what makes mulching work well.
  • Don’t overthink it. Grass has been decomposing on the ground for millions of years. Your lawn can handle it.

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