Does Mulch Kill Grass?

Mulch is generally used to kill grass and weeds. While most mulch products do recommend that any turf be torn up before the application of the mulch, this is not always needed. Below you can learn about the best types of mulch for dealing with unwanted grass and why some may not live up to your expectations.

Will Mulch Kill Grass?

Yes, a thick enough layer of any mulch will kill any grass that is underneath the mulch. Some types of mulch could also sicken or kill certain weed types or weed seeds. Which mulch is best for the grass type you wish to eliminate will depend on that grass type as well as the availability of certain mulches in your area.

Does Mulch Kill Grass and Weeds?

Mulch is much better at killing or discouraging weeds than it is at killing or discouraging grass. Different mulches can also have different effects on grass and weeds. For example, rock mulch discourages all types of plant life while fabric mulch makes it much easier for grass to colonize an area. Below is a list of common mulch types and how effective they are at controlling grass and weeds.

Can Mulch Kill Grass? How Different Mulches Control Grass and Weeds

Not all mulches are great at killing grass. Below is a list of common mulch types as well as how well each type of mulch kills grass and weeds.

• Bark Mulch – Bark mulch is the most common type of mulch you may find at your local garden center or hardware store. This is a decent mulch choice that will shade out most non-stolon grass types at a depth of just 3 inches. Mulch bark is longer lasting than wood chip mulch, but it is also much lighter and may be prone to wind and rain erosion or washing out of beds.
• Fabric Mulch (Landscape Fabric) – Landscape fabric should never be used to cover an area where grass has been or may grow. The grass will quickly colonize the fabric instead of being smothered or blocked by it. This will make the grass more difficult to get rid of in the long run.
• Leaf Mulch – Leaf mulch on its own is not a good way to shade out grass, though it can help reduce or eliminate the need to purchase more mulch to place over places where wood chip mulch or paper mulch has already done most of the work. It also makes a decent cover for plastic or compostable film mulch.
• Paper Pellet or Newspaper Mulch – All paper-based mulches are a good option for controlling all grass and weed types as they quickly fit together, creating a cohesive barrier.
• Pine Needle Mulch – Pine needle mulch wouldn’t be the best option for smothering or shading out grass and weeds, but the slight acidity of the pine needles, if placed in a thick layer, not only weighs down and eats away at the health of the grass, but it can also discourage seeds from sprouting.
• Plastic Mulch or “Weed Barrier” – Thin plastic mulch is often layered under more visually-appealing mulch types for home garden use. It is highly effective and will make your other mulch type last a bit longer. There are even “plastic” mulch barriers available using cornstarch or vegetable polymers or resins instead of petroleum. These products are fully compostable and will break down in 3 to 4 years, leaving no trace behind.
• Rock Mulch – Rock mulch or gravel discourages all plant growth. While some plants may try to climb on top of rock mulch, including stolon-based grasses, their inability to gain a foothold will make them easy to brush away.
• Rubber Mulch – Rubber mulch, while not the most environmentally-friendly option, will discourage plant growth in a similar way to rock mulch.
• Straw Mulch – Straw mulch may be one of the least effective grass control options for general landscaping purposes. It’s also more likely to lead to the development of mold if used in a thick enough layer to control grass.
• Wood Chip Mulch – The general gold standard for most mulch projects, wood-chip mulch is heavy, lasts for several years, and easily smothers grass and weeds of all types. It is often relatively inexpensive and can easily be mounded up into the desired 6 to 8 inches needed for a new mulch bed.
• Mulch Made of Coffee Chafe, Buckwheat Hulls, Peanut Hulls, Cocoa Hulls – Any type of mulch made up of chafe or hulls can be used to kill off annual weeds, weed seeds, and other types of light, mixed vegetation. This is not a great choice for killing any type of grass as these mulch types are too light, easily broken down, and it’s difficult to place a consistent barrier of them. If you do choose this type of mulch, you will need a layer at least 8 inches thick to prevent grass from coming up, but only 4 inches thick to take care of most annual weeds. The thicker layer is not recommended as it can cause problems with mold and water absorption.

Does Dyed Mulch Kill Grass?

Most dyed mulches are dyed using plant-based or other types of natural dyes. While these dyes are usually harmless, they don’t typically last more than a season. Additional dye kits are often sold to re-dye mulch, especially black bark mulch. Often it is better to see if you can find a mulch type that is naturally the color you want to save time and money. For example, instead of dyed red bark mulch, you could invest in the longer-lasting and more effective red lava rock option.

How Do You Clean Up Mulch to Save a Lawn?

No matter which type of mulch may have been spilled, the only option is to rake or sweep it up and carry it away. Afterward, you may want to avoid putting excess pressure on the area as the grass recovers for a few days. Extra water or fertilizer should not be necessary.

Will Putting Mulch Over Grass Kill It?

Yes, smothering any type of grass with enough mulch will kill that grass. However, no mulch is immune to certain types of grass, namely those with stolons, creeping up on top of it. Which mulch you may want to use depends on your budget, environment, and expectations.