Will Grass Grow Through Mulch? How To Prevent It.

Mulching is one of the best ways of facilitating healthy plant growth and development. The practice is beneficial to crops, decorative flowers, lawns, and even trees. However, while mulching is an absolute must for any organic garden, is it an entirely problem-free solution?

Grass will grow through mulch if it is too thin, deteriorated, or of poor or decomposed material. There are ways to prevent or at least slow the growth of weeds or grass in mulch including herbicides, landscape fabric, and creating edges with or without edging material.

That is what we want to find out today. Our focus is on whether unwanted grass and weeds can develop and shoot through a plant or flowerbed’s mulch layer. We will examine preventative measures for this, as well as corrective efforts to stop the invasions. 


Will Mulch Prevent Grass From Growing?

If you have any experience with gardening, you know how difficult it can be to grow grass when and where you need it to. Yet, at the same time, grass has the uncanny ability to grow where you least expect or want it.

Mulch can prevent most grasses and weeds from growing in flower beds for a time. The problem comes when hardy weeds and grasses have time and mulch is too thin, too decomposed, or composed of the wrong material. Mulch can’t prevent all grasses and none indefinitely without other measures.

Along, with weeds, grass is an unwelcome sight in your plant mulch bed. These two are especially threatening to young plants and flowers. Invasive grass species have an accelerated rate of growth that exceeds most other plants. This faster growth means that grass can suffocate your plants’ root network with its own. 

In addition, grass and weeds are competitors for nutrients intended for the plants you want to grow. Their faster rates of growth are facilitated by a constant uptake of minerals, nutrients of water. This uptake is likely to be faster than that of your desired plants.

As you can see, grass can grow through mulch even if it takes certain types and enough time.

How Can Grass Grow In Mulch?

If the right conditions are cultivated, suppression of grass growth can be achieved using mulch. But if conditions are right, grasses and other weeds can and will germinate in mulch.

There are multiple ways that grasses can grow in mulch. Grass invades mulched beds through seeds spread by wind, animals, or even mowers. Germination of grass in mulch can also happen via horizontal runners above ground called stolons or underground known as rhizomes.

Different types of grass employ varied methods for finding suitable soil or soil substitutes to germinate and spread. In order to understand how the grasses spread into the mulched areas in your lawn, it is important to understand what type of grass you have and how it tends to multiply and move to new areas.

Grass Can Spread Into Mulch Beds Through Seeds

Matured grasses near the mulch bed have seed heads that can be blown away by the wind. If some of these seeds fall through the gaps between the mulch and reach the soil below, they will begin germinating. Gaps in the mulch may also allow slivers of sunlight to sneak through, which helps the development of the grass shoots.

Some Grasses Use Runners To Enter Mulched Areas

Certain grass species can also invade through “runners”. Runners are essentially grass stems that inch their way horizontally towards new soil for the grass to colonize.  Aboveground runners are known as stolons. Stolons creep along the surface until they find soil suitable for them to set up roots. Once they have taken root, new shoots emerge, which will form more grass blades…and more runners.

Underground runners are known as rhizomes. Often mistaken for roots, rhizomes operate just below the surface but instead of going further downward, they curve upward when they reach suitable soil. With time, they emerge above the surface as new grass shoots.

Both rhizomes and stolons can invade a mulching layer if it is located next to a lawn or wild runner grasses that are left unchecked.

To read more articles about grass and mulch, I recommend you see some of my others here…

How To Stop Grass And Weeds Growing In Mulch Beds

When it comes to grass invasions, prevention is definitely better than cure. Luckily, there are several ways of doing this. 

Landscape Fabric Prevents Grass Growing Through Mulch

The best preventative measure is landscaping fabric. Mulch on its own is largely effective at stifling grass shoots and weeds, thanks to its blockage of sunlight and physical presence on the ground.

However, coverage gaps, thin mulch areas, and areas dug out by squirrels and other animals can easily facilitate the development of unwanted grass.

Landscaping fabric is laid directly above the bare soil around your desired plants. The mulch is then laid on top of the fabric for double protection. 

If grass seeds somehow find their way past the mulch, they will land on the fabric and fail to germinate due to a lack of soil. Stolons and rhizomes that traverse under the mulch will not be able to take root or shoot up to the ground surface.

Here is a great option for landscape fabric the I recommend from Amazon.

Physical Barriers And Distance Can Hinder Grass Runners

Runners can also be curbed by increasing the distance between the mulch bed and bodies of runner grass. There are several ways to accomplish this.

Edging Helps Prevent Grass Runners

Creating a clean edge and small gap between mulch beds and the grass not only creates a more orderly and aesthetically pleasing lawn, but also deters grass runners and even some seeds from making it into mulched areas.

Edging is a process where grass is cut sometimes to the dirt an inch or two away from a flower bed, sidewalk, or driveway. This creates a gap that makes it harder for runners to cross and find spots to plant roots.

You can make sure to edge runners whenever you mow your lawn before resolving to use herbicides to get rid of wild runner grasses before they colonize your mulch bed.

Edging Material Deters Grass And Weed Spread To Mulch

Bricks and concrete blocks can also be placed to prevent runners from moving toward the mulch. This can also be done with other material according to the design of the lawn and home.

Some homeowners or landscape crews choose railroad ties, rocks, or even plastic forms designed for the purpose. The purpose of any of them is to create a literal wall that the runners will have trouble scaling and a way to create straight even lines for a desired look.

Here is what I recommend from Amazon to create a great barrier and a great look around your flower beds and trees. This plastic flower bed edging material is inexpensive and effective.

Should You Remove Grass Before Laying Mulch?

If you are planning a flower bed or other mulched area, do you need to address the lawn or patch of grass in the way? Or can you simply lay the mulch right over the grass?

Removing grass is essential if you want your mulching layer to succeed in its task. Grass has roots, seeds, and shoots that still have access to the soil under the mulch if left. Hardier varieties will simply grow directly through the protective layer and soon overtake the bed or garden.

This sentiment is especially true when mulching around young plants and flowerbeds. You can get away with a little grass around older plants and trees though.

However, ultimately, one of the main reasons for removing grass and weeds prior to mulching is to ensure the mulch stays in place for as long as possible. The longer mulch stays in place, the better the results. 

As we already discussed, grass and weeds will compete for soil nutrients with your desired plants. It’s advisable to remove the grass to eliminate this competition so your plants grow undisturbed.

Removing grass before mulching will also save you from removing even more grass in the future.

If grass and weeds are allowed to grow and mature, they may eventually develop seed heads and drop more seeds into the ground, which will bring about even more grass and weeds. Clippings from some species of grass can even take root when they fall to the ground.

How To Stop Grass Growing In Mulch

If you were too late for prevention, you’ll be glad to know that “cure” is still an option.

One popular option is to spray emerging blades of grass and weeds with herbicides. This is pretty straightforward, as most of these chemicals have clear application instructions. 

A word of warning though…be very careful with your use of herbicides. Avoid using very strong chemicals if you can, because you may inadvertently cause harm to the plants or flowers you’re trying to grow.

A lot of grasses and weeds are more resistant to herbicides than other plants, which may lead to the use of stronger chemicals.

One household chemical that is low in toxicity, but effective against grass and weeds, is a vinegar and salt solution. This DIY solution is very easy to prepare. Simply mix a gallon of vinegar with a cup of salt and one tablespoon of liquid dish soap. 

Pour the solution into a spray can and spray the grass shoots and weeds when the sun is brightest. The soap prevents the grass from absorbing the solution, which sticks onto the stem and blades. This causes water to exit the grass plant via osmosis and evaporation, which turns the grass brown and kills it. 

If your grass problem is recurring, you will have to take drastic measures.

The best long-medium term solution is to use a rake to remove the mulch from the bed. Next, pluck out any weeds and lay some landscaping fabric on the ground. You can also use newspaper instead of (or together with) landscaping fabric.

Once the fabric (or newspaper) is in place, restore the mulch layer on top of it. This will stifle and, ultimately, kill any remaining grass below the fabric. The layer of fabric and newspapers will also be a germination barrier for any grass seeds that may be stuck in the mulch.

The Final Touches On Grass Growing Through Mulch Beds…

Grass can grow through mulch, but with proper installation it is less likely. Mulch is used for grass suppression as well as a manicured look.

Mulch can add a lot to the look of a lawn with flower beds, banks, and around trees. Keeping grass and weeds from growing in it takes a few simple steps, but without them it will require lots of pulling and tugging from your knees to get out all of the unwanted plants.

This or you will have to carefully deploy herbicides which come with a host of potential problems.

Using edging and gardener’s cloth is a great way to give yourself an advantage in the contest all of us have controlling grass growth.

To read more great articles like this one, see some of my others…




Mathew Booe

Mathew has worked in landscaping professionally for over 10 years. He is a grandpa and frequently interviews other experienced landscapers and lawn care experts who are also grandpas for these articles.

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