Homesteading, Gardening, and Off-Grid Living

How to Lay Mulch Over Grass with Sheet Mulching

By: Zac Friedman

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Are you trying to kill off some grass to start a vegetable garden or build some flower beds? You may be wondering, can’t you just lay mulch over the grass to smother it and then start planting? 

Generally, the answer is no. The grass and weeds will grow through the mulch if you don’t find a way to suppress it, kill it, or remove it first. Grass is surprisingly tough. There are some exceptions. Some species can be smothered with mulch alone.

This guide outlines 8 ways to get rid of grass before starting a garden. There are several ways to go about doing this. You could use cardboard or newspaper to smother the grass. You could use a sod cutter to cut up and remove the grass. Alternatively, you can also spray a pesticide to kill the grass first. 

How to Lay Mulch Over Grass With Sheet Mulching

1. Smother the Grass With a Thick Layer of Mulch

It is possible to kill off grass and perennial weeds by putting a layer of mulch over them. Cut your grass as short as your lawn mower will go then apply mulch on top. Grass needs sunlight to live. If you can block the sunlight, the grass will die off. If you put a thick layer of mulch over the grass, most of it will die. 

The problem is that some patches will survive and grow through the mulch. You’ll start seeing grass poking through after a few weeks. After a couple of years, the grass will just grow back and spread. The mulch will actually help the grass grow as it decomposes and adds nutrients to the soil.  

A pile of wood mulch and a wheelbarrow

Some types of grass are extremely tough to kill. For example, Bermuda grass and St. Augustine grass will grow through the mulch. Even if you apply use a 4 inch deep layer of mulch. Some grass can grow back, even if you till the grass first. Other varieties will die off more easily. 

Generally, this method is not recommended. Before laying mulch, it’s best to either kill off the grass or remove it. This way, you won’t have to worry about it growing up through your mulch. If you decide to use this method anyway, you can spot-treat any grass that grows through the mulch by applying an herbicide.

2. Use Cardboard or Newspaper to Kill the Grass

One easy way to get rid of grass is to lay cardboard or newspaper on top of it before applying mulch. The cardboard or newspaper layer will smother the grass then degrade away. This works because the cardboard or newspaper will take at least 6 months to degrade. Sometimes it will take a year or more. By the time it’s gone, the grass underneath will be dead. This is a safe, easy, and environmentally friendly way to kill off grass. This technique is sometimes called sheet mulching. 

The first step is to gather some cardboard or newspaper. Look for a non-glossy variety with minimal ink. Remove any packaging tape, staples, etc. You can usually find cardboard boxes that people are getting rid of for free. You can find boxes behind businesses. Bike shops are good sources of large cardboard boxes.

Next, lay the cardboard or newspaper over the grass you want to kill. Use 1-2 layers of cardboard or a thick layer of newspaper. When you’re laying the cardboard, make sure there are no gaps or holes or the grass will just grow through. Try to lay it so it overlaps, like shingles. 6” of overlap will ensure there are no gaps, even if the cardboard shifts. Wait for a calm day to do this. If there is any wind at all, the cardboard will blow around. Wetting the cardboard can help hold it in place. You can use some nails or stakes to help hold the cardboard in place if needed.

After laying the cardboard, spread a thick layer of mulch on top of it (2-4 inches of mulch). This will hold the cardboard in place. It will also look nice. Wood chips and bark mulch will work well. Alternatively, you could use straw, pine needles, grass clippings, or shredded leaves.

A pile of cardboard boxes
Be sure to remove any stickers, staples, and tape from the boxes.

One potential issue you can run into is that the cardboard and mulch will increase the thickness of your new garden beds. If your garden is up against a sidewalk or driveway, you may have issues with mulch spilling over. You can prevent this by installing some plastic edging or digging a trench around the edge to catch the overflowing mulch. 

The edges can also be problem spots. Grass may grow up around the edges of the cardboard. One way to solve this is to apply some herbicide around the edges to kill the grass off. You don’t need to apply herbicide under the cardboard but you can if you choose. 

There are several benefits of this method. Most importantly, it works. It’s also easy to do and it’s affordable. You can find cardboard boxes for free. It’s also relatively environmentally friendly. Cardboard boxes and newspaper are made from organic materials that decompose over time. They may introduce some chemicals to your soil but it will be minimal. These materials also decompose completely over time. You never have to remove them. You can plant after the grass is dead. Using cardboard is a simple solution and it is very effective. 

3. Use Landscape Fabric to Smother the Grass

Instead of using cardboard, you could use landscape fabric to smother grass. Landscape fabric is plastic sheeting that is designed to be used under mulch to prevent weed growth. It can also be used to smother grass. 

Simply roll the landscape fabric out on top of the grass that you want to kill then cover the fabric with the mulch of your choice. The grass underneath the fabric will die off. 

There are a few drawbacks of landscape fabric. It’s not great for the soil because it reduces the amount of air and water that reach the soil. It is also difficult to remove. If you decide to plant plants, the plant roots can grow into the fabric. Over time landscape fabric gets torn up and frays. It becomes an eyesore. It is also less environmentally friendly than cardboard. This is because it can introduce microplastics to your soil as it ages and degrades. It will also end up in a landfill someday when you remove it. It’s a plastic product. 

For more info, check out my guide to the pros and cons of using landscape fabric under mulch.

4. Use a Sod Cutter and Removing the Grass

grass

The fastest way to get rid of grass is to use a sod cutter to cut it up into strips. You can then roll it up and throw it away, give it away, or place it somewhere else in your yard. After you remove the sod, you’ll be left with bare soil. You can start planting your new plants and cover the soil with mulch. 

Because a sod cutter isn’t a tool you’ll have to use often, it’s usually best to just rent one. Many hardware stores and tool rental places have them. There are both manual and motorized sod cutters available. 

If you don’t have a sod cutter, you can just use a shovel to dig the grass out. This can be the best option if you’re just dealing with a small area. For example, maybe you’re trying to expand an existing bed by a couple of feet. 

The benefit of using a sod cutter is that it’s much faster. You can remove the old lawn and start planting immediately. It would be possible to go from having a lawn to having a garden in a single weekend. You don’t have to wait for the grass to die off first. If you’re in a hurry, you’re better off using a sod cutter. Removing sod is a pretty labor-intensive job. Be ready to work up a sweat.

5. Torch the Grass

Another way to get rid of grass is to torch it. Fire will kill off the grass quickly. You don’t need to burn the grass to a crisp. Just a couple of seconds of flame exposure will kill it.

This works because the grass leaves can no longer do photosynthesis when they’re burned. The root systems will eventually die off and decompose. Torching or flame weeding is extremely effective. It’s also kind of fun. 

After burning the grass, you can apply a layer of mulch on top. The torch will weaken the grass enough that it won’t come back. There is a chance that some of the grass will grow back if you miss a spot. You can just hit these spots with the torch again to get rid of them. 

6. Use an Herbicide 

Another way to get rid of grass is to spray it with an herbicide. One popular option is Roundup (glyphosate). This is a highly effective herbicide. It will kill the grass quickly and effectively. 

After the grass dies off, you can apply a mulch layer on top. The dead grass will decompose over time. You don’t have to till it or remove it. 

There are drawbacks of using herbicides. Most importantly, they introduce chemicals into your yard. Some people care about this while others don’t mind. Personally, I prefer not using herbicides in my yard but I do still use them on occasion. 

In some places, people are also extremely against the use of Roundup. Probably because it’s been in the news so much over the past few years. If a neighbor sees you spraying it, they could freak out. Some people get really worked up about it for some reason.

There are also some natural solutions to consider if you don’t want to use an herbicide. You can also use vinegar to kill grass. Spray the grass with 5% vinegar and it will die off. The acidity of the vinegar kills the grass. Vinegar is not as effective as a purpose-made herbicide. You may have to spray 2-3 times to make sure the grass is dead. Some grass species can come back after one application. The vinegar will weaken the grass enough that most of it will die off under the mulch. 

7. Use an Old Carpet

Another way to kill off grass is to lay an old carpet over it. Leave the carpet for a couple of months until the grass underneath dies off. You can then move the carpet and start planting. 

You have to remove the carpet before mulching or planting. This can be an effective method but the carpet doesn’t look very attractive while it’s in place. 

8. Use Leaves

A pile of leaves

Leaf litter can also be used to smother grass. Simply lay a thick layer of leaves over the section of lawn that you want to kill then put another layer of mulch on top. 

When you do this, you can use shredded leaves or leave them whole. Whole leaves may work better because they will form into a mat when they get wet. This will help smother the grass. You don’t have to put a layer of mulch on top but it helps and it can look nicer.

How to Prepare the Area

Before you start laying cardboard or anything else, it’s best to cut the grass short. This way, there will be less material for decomposers to break down after the grass dies off. If the soil is dry, you should also water. The material will break down faster if it’s moist. 

It’s also a good idea to edge around the area where you’re trying to kill the grass. Simply use an edger to cut out the shape of your new garden. This is important because grass and weeds will tend to grow around the edges. Edging will help prevent that. It will also look nicer. You could also install some type of edging material like stones or plastic edging. 

After prepping, you can start laying the barrier. You can do this at any time of year. There is no best time. Early spring is perfect. 

Wait Before You Start Planting

If you apply mulch over grass using the cardboard method, you should wait until the grass dies off before you start planting. Ideally, you should wait 6 months. If you can’t wait that long, you can start planting after 6-8 weeks. 

After a few months, the cardboard will be partially decomposed. This will make it easier to break through. The grass underneath will also be dead.

If you plant immediately after applying the cardboard and mulch, grass might start growing up through the holes you make for your plants. It will also be difficult to break through several layers of cardboard. 

If you remove the grass with a sod cutter you can plant immediately. If you kill the grass with an herbicide, you might have to wait anywhere from 1 day to a couple of months before you can plant, depending on which herbicide you use. It will say on the bottle how long you should wait. For Roundup, you usually only have to wait a day or two. 

When planting, make sure the mulch isn’t touching your plant stems. It can cause mold. If you’re looking for a low-maintenance garden, consider planting native plants. They are good for the environment because they don’t need as much water as grass. They can also look nice.

A flower growing out of mulch

The Best Mulch to Apply Over Grass

You can apply any type of mulch over grass clippings. Wood chips and bark mulch are popular options. They both come in a range of colors and textures and are long lasting. I’m a big fan of cedar mulch. You could also use pine needles, grass clippings, or shredded leaves. These mulches are nice because you can usually get them for free. Straw and hay are also a popular option for vegetable gardens. When choosing a mulch, make sure it doesn’t contain any weed seeds. 

It is also possible to use an inorganic mulch such as river rocks, pea gravel, lava rocks, or rubber chips. Generally, it’s best to put landscape fabric under inorganic materials. This is because they tend to sink into the soil over time. They don’t degrade so it’s best not to have a bunch of rocks in your soil.  

If you plan to plant in your garden, it’s a good idea to apply a layer of nutrient rich material over the grass before you add mulch. For example, you could add a layer of compost or manure. This will help restore some nutrients to the soil after the grass dies off. 

Also, remember that you will have to refresh the mulch periodically because organic matter decays. On average, mulch degrades at a rate of around 1” per year. Some organic mulches, like straw, degrade much faster. You may have to add some fresh mulch once or twice per year to keep the grass and weeds down. You don’t need to remove the old mulch. Instead, you can just apply a fresh layer on top.

You don’t want to apply too much mulch or you could experience problems with mold. It will also block water and air from reaching the soil. 

Bark mulch

My Experience

A couple of years ago, I decided I wanted more garden space. The problem was that there was grass growing where I wanted to plant. 

I was feeling lazy so I decided to just put some mulch over the grass to smother it. It kind of worked but the grass did start growing through in several sections. I ended up using an herbicide to kill off the grass where it started growing through. 

Last year, I decided to expand my garden space by building a new garden bed on the other side of my yard. This time, I used the cardboard method and it worked surprisingly well. It was also really easy to do. I found some free cardboard boxes behind a grocery store.

The cardboard broke down faster than I expected. I started planting a few months after I applied it. So far, I haven’t had any issues with grass sprouting up in my new garden. I will use this method again in the future if I decide to expand my garden further. In my opinion, cardboard is the best way to smother grass. 

It’s always a good idea to use a ground cover in your garden instead of leaving the soil surface bare. Mulch will help keep the weeds down, retain moisture, reduce erosion, and insulate the soil. Mulch will also improve the soil structure as it degrades. It also adds valuable nutrients to your soil.

When you cover your grass with mulch, you’ll spend less time on lawn care. You will still have to do some weed control. Eventually, some weeds will start sprouting from your mulch. It’s unavoidable.

There are plenty of different materials you can use to smother the grass including cardboard sheets, newspaper, and landscape fabric. You could also remove grass with a sod cutter or use a pesticide to kill the grass. Whichever method you choose, I hope this guide helps make the process a little bit smoother and easier. 

Have you applied mulch over grass? What were the results? Share your experience in the comments below!

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How to Lay Mulch Over Grass With Sheet Mulching

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