The Can, Why, And How Of Putting Mulch Over Grass

If you do gardening from time to time, you’ve probably asked yourself the question…”Can I put mulch over grass?”.

Technically, yes you can. And practically, it’s a good thing, as long as you know what you are trying to achieve.

Mulching grass is a great way of converting otherwise unused land into vegetable and flower gardens.

You see, the mulch essentially kills the grass, weeds, and whatever other vegetation it is laid upon as it cuts off its air supply and access to sunlight.

Let’s explain how this works in more detail.

Can You Put Mulch Over Grass?

Yes, you can put mulch over grass.

But in order to achieve the most desirable results – that is, creating enriched soil that is suitable for plant and vegetable growth – you need to perform a method known as sheet mulching or smothering.

It’s a natural method to suppress and kill grass, weeds, and other foliage by cutting off sunlight, and air supply.

There are two variations of sheet mulching – deep sheet mulching and shallow sheet mulching.

Deep sheet mulching involves using alternative layers of green and brown mulch with a paper or cardboard layer. The end result can be a foot or more of mulch.

Shallow sheet mulching also uses a cardboard or paper layer along with a single layer of brown mulch, resulting in 3 or more inches of mulch depth.

Both of these methods work great for enriching the soil with nutrients and killing unwanted vegetation.

Over time, the grass stops growing, and the mulch, dead grass, and barrier materials (like cardboard and paper) decompose, enriching the soil and providing a new planting area.

The whole process can take months or even more than a year.

Why Put Mulch Over Grass?

As we mentioned, putting mulch over grass has several benefits which we will go into further detail here.

Weed Suppression

One of the primary benefits of putting mulch over grass is to suppress weed growth. By blocking the light and air supply, the grass and weeds are starved and unable to anchor their roots deep into the soil. This method is effective for all types of grass and weeds, including perennial and annual varieties.

Why Put Mulch Over Grass

Soil Enrichment

When mulch, grass, and other materials decompose, they add nutrients to the soil. This enriched soil promotes healthier plant growth and ensures the long-term success of lawn replacement projects.

Environmentally Friendly

Sheet mulching is an environmentally-friendly way to suppress grass growth. It does not require the use of harmful chemicals and can be done at any time of the year. Additionally, the materials used for sheet mulching are often affordable and readily available.

Aesthetic Appeal

Applying mulch over grass can transform your lawn into a beautiful vegetable or flower bed. By replacing sections of your lawn with mulch, you create a visually appealing and functional space that adds value to your property.

Saves You Time (Sort Of)

Putting mulch over grass saves you time and the intense manual labor of having to dig up the grass yourself.

While the process is easier and less time-consuming initially, this method requires more patience as you’ll have to wait for the mulch to naturally kill the plants, weeds, and grass. This can take several months or more.

Our advice is to plan in advance. Mulch the grass at least a season before you decide to plant.

What Type Of Mulch Should I Use? Organic Or Inorganic?

There are two main kinds of mulch – organic and inorganic.

If you plan on killing the grass and then using it for planting vegetables, flowers, fruits, and so on, we’d recommend using organic mulch.

Organic mulches are made of organic materials like straw, leaves, wood chips, grass, and pine needles. These mulches decompose and enrich the soil, making them ideal for promoting healthy plant growth.

Just like organic mulch, inorganic mulch will also kill the grass by blocking sunlight and suppressing airflow.

Inorganic mulches, such as black plastic, geotextiles, stones, and gravel, are suitable for boosting your garden’s aesthetics but will not add any nutrient value to your soil.

Inorganic mulch is somewhat easier to work with. Once you lay the mulch you can pretty much leave it and benefit from the added visuals it gives to your lawn, all the while it will be killing grass and weeds. However; we’d advise using organic mulch if you want to prepare the grass for a flower or vegetable garden in the future.

How To Lay Mulch Over Grass: A Step-by-Step Guide

And now we get to the how part of this article. You may be wondering how we lay mulch over grass. It’s a fairly straightforward process.

Before you start laying mulch over grass, we advise to use the following materials:

  • Lawnmower
  • Newspapers or cardboard (avoid glossy colored pages)
  • Water
  • Compost (optional)
  • Mulch (e.g. wood chips, straw, or bark)

Follow these steps to lay mulch over grass:

1. Cut the Grass

Mow the lawn. Cutting the grass short makes it easier to lay newspapers or cardboard over it, especially when it is an even surface.

If your grass is already short (say less than 3″ long) you may skip this step.

2. Remove Perennial Weeds

Manually remove any perennial weeds, such as oxalis, dandelions, and onion weeds from the area. These weeds re-sprout yearly from the same root and can regrow after the mulch has broken down.

3. Water the Soil

To hold the newspapers or cardboard firmly in place, water the soil in intervals. Apply a small amount of water, let the soil soak it in, and repeat as necessary.

4. Place Newspapers or Cardboard

Place sheets of newspaper or cardboard over the grass. The newspapers should be 10-12 sheets thick, and the edges should overlap by 4 inches to ensure thorough coverage. If using cardboard, use a single layer for the best results.

5. Wet the Newspapers or Cardboard

Before adding mulch or compost, be sure to wet the newspapers or cardboard. This will help it stick to the soil and hold it all together. Be careful not to tear the newspaper.

6. Spread Compost

Spread a couple of inches of compost on top of the newspaper or cardboard. 3 inches is usually sufficient. This layer aids in decomposition and provides nutrients to the soil. Though this isn’t absolutely necessary, we’d recommend it to speed up the whole process and further add nutrients to your soil.

7. Apply Mulch

Apply Mulch

Spread the mulch over the newspaper or cardboard, ensuring a thickness of 3-6 inches to block sunlight. Be careful not to tear or shift the newspaper or cardboard material when spreading the mulch. The mulch will hold the compost in place and decompose over time, adding more nutrients to the soil.

8. Water the Mulched Area

Water the mulched area to compact the mulch and help it settle.

9. Wait Before Planting

It’s advisable to wait for about three months or more before planting in the mulched area. This timeframe allows the mulch to kill the grass and break down the barrier materials, ensuring a healthy environment for your new plants.

How To Prevent Grass From Growing Through Mulch

Although mulching over grass discourages its growth, some grass may still sprout through the mulch. Here are some methods to prevent grass from growing through:

Use Landscaping Fabric

Place landscaping fabric over the soil before covering it with mulch.

The fabric acts as an additional barrier against sunlight and air, preventing grass from growing. Grass that reseeds above the fabric cannot penetrate its roots deep into the soil, making it easy to handpick.

Vinegar Solution

A vinegar solution mixed with a small amount of liquid dish soap can be an effective natural grass killer.

The soap helps strip the waxy protective coatings of grass, which allow the vinegar to be more potent. Spray this solution on emerging grass to kill it.

Create Defined Edges

Separate the mulched grass from the rest of your lawn. A deep edge will help prevent grass from other parts of your lawn from growing under the soil and reaching over.

Avoid Chemicals

Be cautious before using chemicals to kill grass, as they can harm the environment and inhibit the growth of new plants in the future as they may contaminate the soil.

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