How To Use Grass Clippings to Mulch Your Lawn

Over many years of maintaining pristine lawns, I’ve seen grass clippings become both a blessing and a curse. While they can nourish your yard, improper use might invite unwelcome guests, like weeds or pests. I’ve helped countless homeowners learn how to use their grass clippings as mulch. This will help your lawn stay green without becoming a breeding ground for problems. Here’s what you need to know.

When Not to Mulch With Clippings

Most of the time, when you mow, you leave grass clippings on the lawn. Mulching blades on lawnmowers chop up clippings into tiny pieces that break down rapidly. The fresh clippings decompose quickly and release nutrients back into the soil. 

But, sometimes, bagging clippings makes more sense. You should bag them when you mow an overgrown lawn for the first time. Long grass clippings clump together and smother grass if left on the lawn.

If you have to mow when the grass is wet or if it has many weeds, it’s also best to use a bag. Wet clippings decompose slowly, and weeds will spread seeds if left on the lawn. It’s also a good idea to bag clippings from chemically treated grass and weeds.

Advantages of Grass Clippings as Mulch

Using grass clippings as garden mulch offers some potential benefits.

Disadvantages of Clippings as Mulch

While using grass clippings as an organic mulch has benefits, remember that it has some potential drawbacks. Green clippings decompose quickly, especially in hot weather, and can leave plants under-mulched if you don’t mix them with new clippings consistently.

Applying more than an inch of fresh clippings can cause the trimmings to mat and prevent water and air from reaching plant roots.

Decomposing green materials generates heat. Too thick of a layer can burn plant roots and crowns. Ideally, limit each mulch application to an inch.

Any weed seeds that mix into your clippings can sprout later in your garden or wherever you throw your organic mulch. Remove weeds from your lawn before bagging them for mulch or leaving them to mix back in with your lawn.

Similarly, fungal diseases and pests, such as grubs, may inadvertently transfer to your garden plants with your new grass mulch.

Finally, clippings may contain herbicide or fertilizer residues that could damage garden plants. Avoid using clippings after chemical applications.

Do Clippings Increase Thatch?

Thatch is a layer of dead and living grass shoots, stems, and roots that accumulate between the soil surface and the green grass blades. A common debate among homeowners is whether or not leaving grass clippings on the lawn contributes to thatch buildup. Let me put your mind at ease: Properly managed grass clippings don’t significantly increase thatch.

While excessive thatch can be problematic, grass clippings are not a major contributor to thatch buildup.

Here’s why:

1. Quick decomposition: Grass clippings are primarily water and break down rapidly, usually within a few weeks. They don’t stick around long enough to become part of the thatch layer.
2. Different composition: Thatch is mainly composed of grass roots and stems, which contain lignin — a tough organic compound that resists decomposition. Grass blades, which make up most of the clippings, contain very little lignin and decompose much faster.
3. Beneficial microorganisms: Leaving grass clippings on the lawn can actually help reduce thatch by promoting the growth of microorganisms that break down thatch.

However, if you always leave very long grass clippings on the lawn or if your soil doesn’t have the right microorganisms to break down quickly, clippings could make thatch buildup. This is why it’s important to mow regularly and maintain a healthy soil ecosystem.

Remember, a small amount of thatch (less than 1/2 inch) is beneficial for your lawn. It helps moderate soil temperature and provides a cushion for foot traffic. If you’re worried about too much thatch, aeration and proper lawn care are better ways to fix it than removing grass clippings.

Best Practices for Mulching With Grass Clippings

Follow these tips to use grass clippings successfully and safely as mulch:

• Let clippings dry and brown completely before spreading them in the garden. This prevents matting, reduces heat buildup during decomposition, and gives weed seeds time to die. (Pro Tip: Spread in a thin layer of grass clippings on a tarp or concrete driveway. After one to two weeks, they should be ready to use as mulch.)
• Apply clippings in layers one inch deep or less, allowing them to dry between applications to prevent matting and smothering plant crowns. Only apply one inch of dried clippings at a time before letting them dry out for a few days. Adding too much at once can suffocate plants.
• Pull weeds from your lawn before you mow to reduce weed transference.
• Avoid using clippings from lawns recently treated with weed killers, fertilizers, or insecticides. Wait at least two mowings after any chemical applications.
• Monitor plants for any pest outbreaks after applying grass clippings mulch. Treat pests immediately to avoid spreading issues.
• Rotate grass-clipping mulch with organic mulch like shredded leaves or wood chips. This practice provides a variety of nutrients and prevents matting issues.

Final Thoughts on Mulching With Grass Clippings

Mulching with grass clippings can benefit your garden and reduce expenses for mulch and fertilizer. However, fresh green clippings present some risks in terms of matting, heat buildup, and weed propagation that require careful management.

I find that the best approach is to leave dried grass clippings on your lawn whenever possible. Sometimes, you must bag clippings. With the right drying and layering methods, along with pest and weed control, you can reduce the small risks of grass clippings mulch. Consider the pros and cons to decide if grass clippings mulch fits into your garden plans.