Can You Mulch Over Rocks? How To Do It The Right Way

When it comes to mulching, homeowners are spoilt for choice, especially when it comes to decorative landscaping. With organic and inorganic mulches all offering unique advantages and drawbacks, making a decision is a real headscratcher.

If you already have rock in place in your garden or flower bed, you can mulch overtop of it as long as you do it using landscaping fabric and at least 2 inches of organic mulch. Though rock lasts longer than the one laying it, mulch will have to be replenished at least once per year.

Today we take a look at how to landscape rock relates to more traditional mulches. We discuss whether you can lay mulch on top of rocks, as well as the best way of doing so. It’s also important to understand the associated costs of replacing rocks with mulch. Let’s get started.


Can Mulch Be Laid Over Rock?

If you have already created a flower bed using rocks as the mulch or want to reclaim part of a driveway or French drain, then is it possible to simply lay mulch right overtop? Is that even a good idea?

You can definitely mulch over landscaping rocks. Though some may advise to first take up the rock before putting down a layer of much, it is not necessary. The rock underlayment will help with drainage, weed control, and soil erosion. They are also a good layer of protecting against pests.

Landscaping rocks present many benefits for your yard. In addition to their contribution to your home’s aesthetics, landscaping rocks can also serve as a barrier that minimizes soil erosion and weed growth. They are also resistant to foot traffic and allow for excellent drainage. 

Let’s not forget that rocks are also less likely to attract pests or be blown away by the wind. The cost of maintenance is also kind on your wallet and there is virtually no limit to the choice of rocks you can use. Also…rocks last for a very long time.

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Drawbacks To Mulching Over Rocks

However, landscaping rocks do have inherent drawbacks that may lead a homeowner to cover (or replace) them with mulch.

Firstly, landscaping rocks may have detrimental effects on your soil and plant life. Rocks tend to have very high rates of heat absorption, which may prove extremely harmful to soil and microbes, especially in the hot summer months. This leads to plants getting undernourished, dehydrated, and stressed.

Rocks also disrupt soil pH levels. Plants tend to favor slightly acidic soils, but the chipping away of rocks raises pH levels and makes the soil more alkaline. Alkaline soils may seriously inhibit plant growth. Highly sensitive plants may also be killed if pH gets too high.

To counteract the negatives of landscape rocks, we recommend that you remove them and lay out traditional mulches instead. However, if removing the rocks is too tedious or if you’d rather not get rid of them, you can also place the mulch over the rocks.

Drawbacks To Organic Mulches

The most frequently used forms of mulch in this regard are wood and pine needle mulches.

Because they are organic mulches, these two will decompose over time and enhance soil nutrition, which benefits plant life. The added organic matter will, in turn, increase the number of soil microbes. More microbes equals greater nutrition for plants

Wood also has much lower heat absorption levels than rocks, which can help alleviate stress on plants. Organic mulch also helps with soil moisture retention, meaning you won’t have to water your plants as much.

Unfortunately, mulching over rocks may increase maintenance demands and costs. Organic mulch, in particular, requires more frequent replacement because it decomposes and can be swept away by wind or water. 

Organic mulches may also harbor weed seeds, which may germinate into a full-blown weed problem, which means more work for you. You have to be very mindful of where you source your mulch.

How To Put Mulch Over Rocks

If you have decided that laying mulch down over rock is the best for your situation, then what is the best way to do it? Do I need some sort of weed control method and how thick should it be put down?

Applying mulch over landscape rocks is a straightforward process. All you need is the mulch, a pitchfork, landscape fabric, and a rake for distributing the mulch evenly. It is best to spread the mulch in at least a 2 inch layer to keep down heat and the water from leaching to the rocks below.

  • The first thing you need to do is lay the fabric on top of the landscape rocks. The fabric will serve as a barrier between the rocks and the mulch. This barrier will help you when it’s time to reapply the mulch or remove the landscape rocks entirely.

Another important benefit of landscape fabric is the weed control aspect. It prevents roots from tapping into soils below. This keeps any weeds that do enter the mulched area limited to shallow root systems that are easily removed.

  • Make sure you measure the area you want to cover with fabric. Cut sufficient lengths of fabric and create gaps for any plants in this area. If you’re using overlapping sheets of fabric, make sure to overlap them by at least a ¼ inch to reduce the chances of weed growth.
  • The final step is to lay your chosen mulch on top of the fabric. Use a rake to distribute the mulch as evenly as possible. We recommend that you apply enough mulch for a 1-2-inch layer. If you have too much mulch, bag the excess. Mulch must not be overly concentrated in one spot.

A word of warning…do not apply wood mulches close to wood sidings. Weed seeds are not the only things wood mulch may be harboring. Termites (or worse…termite queens) might be lurking in the mulch, so be very careful.

If you are interested in other mulching, flower bed, or garden articles, I recommend some of my others…

Is Mulch Or Rock Better For Landscaping?

The answer to this question may vary as it is dependent on a particular homeowner’s landscaping needs. Some prefer rock and stones to mulch, while others only use organic mulches.

For larger bushes and plants rocks are a better low maintenance solution than organic mulch. For smaller more delicate annuals and perennials, mulch and its water retention qualities are the better choice. For a great look and efficient garden or bed, a combination of both is a great choice.

We’ve already touched on some of the benefits and drawbacks of mulch and rocks. Determining the better choice depends on what you are trying to achieve with your yard. Both choices can facilitate great aesthetics but, as the saying goes, beauty is the eye of the beholder. 

If your top priority is vibrant plant life, then organic mulching is the way to go. These mulches boost soil nutrition and minimize evaporation of water from the soil. Additionally, decomposing mulch helps maintain soil acidity, which most plants benefit from.

That said, you must remember that organic mulch does not last forever. You will need to reapply it in the future. This can be both expensive and time-consuming. You also have to worry about your mulch being carried off by the elements, which only adds to the maintenance hassle.

Rocks are, generally speaking, the more maintenance-free choice. With a wide range of rock types, you can have your pick of colors and textures to make your home stand out.

However, as we’ve already seen, rocks are not as conducive to healthy soil and plants, so take heed. Some rocks are also expensive to buy, which could counteract the maintenance costs associated with mulch.

How Do You Replace Rocks With Mulch?

To replace rocks with mulch, you will first have to remove the former first. This is usually a major drawback to covering over rocks.

Removing landscaping rocks is a tough task, especially if they are mixed with soil. The simplest way is to use a shovel and a wheelbarrow. You can also get a friend or neighbor to lend a hand.

Simply shovel the rocks into your wheelbarrow(s) and take them away from the yard. Use a rake to gather smaller rocks into piles and shovel them into the wheelbarrow until only soil remains.

The next step is to lay the mulch onto the bare soil as directed above. Ensure the mulch layer is 1-2 inches thick and it is highly advisable to use landscaping fabric of some kind in order to keep down the unwanted weeds and grasses. 

How Much Does It Cost Tor Replace Rocks With Mulch?

The cost of replacing landscape rocks and mulch can vary drastically depending on your location, where you source the mulch from, and any labor costs.

The whole process can cost you a grand total of zero dollars if you can source the mulch for free and carry out the replacement job by yourself or with some friends.

However, if you cannot source free wood mulch, you can expect to pay at least US$3 for a bag (2 cubic feet) of basic hardwood shavings. If you want richer woods like cedar, you might have to pay anywhere between $7-$10 per bag.

All in all, expect to pay $15-$60 per cubic yard, assuming a cubic yard covers 100 square feet with a 3-inch mulch layer. Delivery costs are another consideration, and these can vary greatly depending on your location and dealer.

The Final Touches On Laying Mulch Over Rock…

For the monumental task of removing a lot of heavy rock layers from beds or driveways, it is advisable to hire a crew with the right tools to make the job quicker and easier.

For smaller areas, it can be done, but simply covering over the stone with a layer of thick organic mulch just may work for your situation. Rock is a great conductor of water in overly wet areas as well.

For some plants like Roses, rock is even advisable at the base of the root system to wick away water. This helps the roots not decay or rot.

Be sure to use landscaping fabric in order to control weeds and grasses trying to intrude into your bed or garden.


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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