Rock vs Mulch — Which One is Better?

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When used properly, rocks can add a touch of beauty to your garden. I’m sure you’ve seen stunning gardens with rocks lining walkways or stylishly diverting the water flow on a property. But did you know rocks can also be used as mulch for your flower beds or around your trees?

Today you’ll learn the details of rock mulch and which types of stones are commonly used. We’ll also detail the best ways to use each type of stone mulch in your landscape design plans.     

This article will also compare traditional mulch and rock mulch side-by-side so you can see what each of them brings to the table, which one is better, and which is cheaper.  The good, the bad, and the ugly.

Keep reading to the end of the guide to learn steps to installing rock mulch.

Garden using rock mulch instead of organic mulch with proper instructions

Rock Mulch

Rock mulch is ornamental pebbles or stones that act as a decorative ground cover on flower beds, around tree bases, fire pits, gardens, pools, ponds, and a host of other applications.  Pea to ping-pong ball-sized gravel (sometimes much larger) are sourced from river beds or areas with rocky terrain.  The gravel is available in a wide variety of textures, colors, and dimensions. 

The multitude of textures and colors affords homeowners the ability to be very precise in their landscape design choices.  With traditional mulch, you’re usually limited to choosing from different shades of brown.  Even “red” mulch has a brownish tint to it.

Rock has many advantages and disadvantages to organic mulch

Types of Rock Mulch

Decomposed Granite

Decomposed granite is the most common igneous gravel formed as hot magma or lava cools and solidifies.  It is composed of several other minerals that include mica, feldspar, and quartz.  The solidification process results in the formation of large crystals that flake and crumble over time.

Decomposed granite is what is left over after the crystals undergo natural weathering and fracture into smaller pieces. 

This landscaping gravel is available in over 30 colors.  DG, as they refer to it in professional circles, can be bought as rough stone or as a finer material that has been further crushed and screened depending on what you will use it for.

Its versatility, ease of installation and maintenance, and excellent drainage are a few reasons people choose decomposed granite.

Applications for this landscape stone depend on the form that you purchase it in. 

Decomposed granite can be a form of rock mulch

The forms and their applications include:

Natural Decomposed Granite

Natural DG works best in areas of your lawn or garden that grass and other plants have difficulty growing.  It will not attract pests to the area and lasts longer than most other varieties of mulch.  It has the bonus of providing the soil and surrounding plants with small amounts of nutrients.

Decomposed Granite With Resin

Combining decomposed granite with resin results in a more permeable and natural-looking form of asphalt.  Often it is used in areas instead of asphalt because it is easier to install and remove while still providing a solid surface that can withstand regular traffic.  You will find this form of DG on playgrounds, pathways, and some driveways.

Decomposed Granite With Stabilizer

You can use this stabilized form of the landscaping gravel to build small pathways or even a patio surface.  The DG with stabilizer is added and tamped down onto the soil or other rough gravel to form a solid surface that is easy to maintain.

Pea Gravel

The stones that comprise pea gravel usually come from river stones that have been rounded and smoothed by flowing water.  It has earned its name because it is about the size of a pea.  Pea gravel is naturally sourced, so don’t be surprised if you find a larger rock or two that seem out of place. 

Pea gravel is used as a decorative alternative to concrete in driveways, patios, and walkways.  Its natural colors offer a comparable option to traditional mulch with the added benefit that it won’t deteriorate on your lawn.  If you have little time to spend working outside, pea gravel is an excellent option.

Pea gravel is easy to work into a landscape design and comes in a wide selection of natural colors.  Plus, it is less expensive than other types of rock mulch.

One of the major problems with pea gravel is its ability to travel.  Unlike crushed gravel, it doesn’t lock into place.  Instead, it rolls over one another and has a propensity to wind up out of place.  So using it on a sloped landscape or an area without a defined boundary may leave you with the occasional scattered stone.

Pea gravel is a more inexpensive rock mulch

Lava Rock

As its name would show, this landscaping rock is created when a volcano erupts and spouts lava onto the surface.  Over time, the lava will cool and solidify.  The rock is then harvested and broken down into the red or stones you find in your landscape.

The reddish tint on the stone comes from the oxidation of iron present in the lava during the eruption.  Basically, it rusts.  The black stones do not differ from the red except in color.  They simply did not oxidize the iron during the volcano’s blast.

These stones look best in yards where they match the surrounding terrain.  Especially in desert landscapes. 

Compared to other types of stone mulch, it is lightweight and easier to spread through your property. 

Lava rock is a good option for homeowners who have problems maintaining the soil temperature and moisture level.  It will trap the heat of the sun during the day and release it at night.  Its ability to regulate soil temperature helps it retain moisture in extreme environments by slowing water evaporation.  Putting down a weed barrier underneath it creates an effective weed suppressant in your flower beds.

Be careful when making lava rock your choice for your home or garden.  Its color and texture can prove very dramatic and pronounced, especially if you choose to use the red lava rock. 

In the end, aesthetics come down to your personal preference.  But if you’re planning on putting your home on the market soon, then choose something more in the middle of the road with strong, natural base colors. You’ll avoid alienating any potential buyers.

Remember, the first thing people see when they walk up to the front door is the landscape surrounding it.  A healthy lawn with good landscaping decisions can add up to 20% to your home’s resale value.

Besides, if you decide you don’t like it after spreading it throughout your garden beds, it is an absolute nightmare to remove it.  So be sure to do your homework before you commit to using lava rock.

Lava rocks is an infrequent stone cover for gardens.

River Rock

The name of these landscaping stones tells you all you need to know about where they were sourced.  Over time flowing water has rounded, smoothed, and flattened the surface of these stones.  It shaped them into the stones that are a foundational part of many homeowners’ landscape and hardscape designs.

Don’t get river rock confused with pea gravel because they are both harvested from river beds.  Pea gravel is smaller and more consistently uniform.  You can buy a load of river rock that will have stones that range from ¾” to 5″ in the same lot. 

It is very useful when used correctly in your design choices.  Whether your goal is nothing more than a simple accent or if you’re in the middle of reimagining your home’s curb appeal, river rock lends itself to an assortment of applications.

These stones can add a sophisticated, defined look to the borders of your flower bed.  Laying it onto a path or walkway can give your property an elegant yet rustic functional addition to your backyard. 

If you have a drainage problem on your property and you need to divert the water, river rock can kill two birds with one stone.  Simply create a dry creek bed that flows into a rock garden or other water collection point.  You can craft your creek bed to bend and turn as you wish to meet your design aesthetic. 

Because river rocks are round, they do not lock together like sharper gravel .  The water freely flows down and absorbs into the soil.  Lawns with poor drainage can wind up damaging your home’s foundation as it runs off the soil.

Whether you’re creating a Zen garden to relax in or building a retaining wall to curb soil erosion, river rock is a staple in landscapes today. It can function effectively in different capacities and give your property an appealing, distinguished look at the same time.

River rocks add a beautiful touch when used as rock mulch.

Rock vs. Traditional Mulch: Which is Better

It is better to use rock in certain circumstances and traditional mulch in others. Rocks are better at weed-prevention than mulch and are also lower maintenance. Stones can also add to the aesthetics of a property. However, rock cover is not good for gardens that receive a lot of sun because they retain more heat than mulch.

Ultimately, it all comes down to personal preference.

Before you make your final decision about your landscape mulch, ask yourself what you’re using it for.  How much time are you going to commit to upkeep and maintenance?  Are there any issues with your lawn that you’re trying to solve with this mulch? 

These are but a few of the important questions you need to ask yourself to diagnose which type of mulch is going to work best for you. 

If you don’t want to spend a lot of time working with the landscaping mulch and money isn’t an issue, then choosing a stone mulch will give you what you’re looking for.  You won’t have to spend time outside working on the stones after their initial installation. 

If you enjoy spending time in your garden and are proud of your plants and flowers’ vibrant growth and blossoming, then using organic or other bark mulches on your property is what you will probably decide on using. 

Each of these mulches, whether stone or organic or bark, comes with its pros and cons about what it can offer to the homeowner.  Remember that there’s no rule written down in some age-old lawn care text that says you cannot use both on the same lawn.  If you’re happy with its form and function, that’s all that truly matters. 

Rock can be seen instead of organic mulch.

Which is Cheaper?

In terms of initial investment, rock mulch is more expensive than organic or bark mulch by two to three-fold.  The stones’ weight will increase shipping and delivery costs.  However, stone and gravel mulches are only paid for once.  Organic mulch is a reoccurring cost that you will pay every time you need to replace it.

You will have to replace the shredded bark or other organic mulch at least once per year because it breaks down over time and adds nutrients to the soil.  Rocks do not break down and are very low maintenance.

You’re going to wind up spending money no matter the route you choose. It’s up to you to decide whether you want to spend a larger amount of money upfront or spend the same amount of money (or more) over an extended period.

Your budget could be the most significant determining factor in which of these mulches you choose.  If money is your primary consideration, then get creative.  Start composting to save money on your organic mulch. The costs you reduce by using this simple, homemade organic mulch to accentuate and fertilize your plants and shrubs will add up.

Do Rock Mulches Hurt the Soil?

Stone mulches are heavier than their organic or shredded bark mulch counterparts and can cause compacted soil in areas that have a thicker mulch layer or larger stones.  Compact soil causes issues that range from water pooling on the surface to causing roots to suffer because they cannot readily access the nutrients, air, or water essential to survival. 

Besides compact soil, you could also consider the fact that rocks do not nourish the soil with nutrients like pine bark mulches and other wood chips do as they decompose.  Rock mulches will absorb the heat from the sun and raise the temperature of the soil.  This will dry out the soil and create drought-like conditions for the plants’ root systems.  If you do not have drought-tolerant varieties growing in your gardens, the plants will undergo stress that can compromise their health and growth rate.

Over time, stones can create an alkaline pH level in your soil.  Trees grow best in acidic soil conditions.  If you’re using rock mulch around your tree bases, you might compromise their health unbeknownst to you.

Garden planted with both organic and rock mulch

Pros and Cons of Using Rock

Pros

  • Very low maintenance.  You won’t spend much time keeping these mulches up after they are installed.
  • An effective method of controlling weed growth.  When installed correctly, they will keep weeds from encroaching on their turf. 
  • Inhibit fungi growth because they do not retain water.
  • Variety of different applications that are both functional and aesthetically pleasing.
  • More effective at preventing soil erosion and runoff than wood-chips or bark mulches.
  • Good in areas that are prone to wildfires.  They are inflammable, so you can line these mulches as close to your structures as you please.
  • Extremely durable and could last, literally, for the rest of your life.
  • Decreases how much water evaporates from the soil and is available to your roots

Cons

  • Rocks do not break down.  So they do not supply the soil with essential nutrients.  Plantlife in the area may require supplemental feeding.
  • They can be heavy, awkward, and difficult to install compared to bark mulch.
  • The upfront cost can be up to 6 times the amount you would spend on traditional landscape mulch.
  • Potential to increase the soil temperature to unhealthy levels by retaining heat from the sun.
  • Have the potential to cause compacted soil where they are placed around your home
  • The heft of the rocks and the weed barrier make it very difficult to return to plant annuals on your property

Pros and Cons of Using Traditional, Organic, or Bark Mulch

Pros

  • Lighter and easier to work with than stone mulches.
  • It breaks down over time and returns essential nutrients to the soil.
  • Smaller upfront cost than you encounter with mulch rocks.  Although the cost will recur from time to time, it’s not prohibitive.
  • Placing a mulch ring 3′ to 6′ around a tree base can almost double its growth rate.
  • Retains water that can be absorbed into the plants’ root systems and encourage healthy growth.
  • Helpful at preventing soil runoff and erosion.  Rock mulches do this better, but you still receive some prevention capability.
  • Regulates the soil temperature throughout the year.
  • Effectively controls the growth of weeds and their seeds.
  • It does not require edging or a piece of landscape fabric to act as a barrier.

Cons

  • Replace traditional mulches at least once per year.
  • The reoccurring cost associated with having to purchase new organic mulch, bark mulch, or wood chips every year.
  • It can be washed away by heavy rains and violent winds easier than rocks.
  • Letting mulch sit can attract unwanted egg-laying insects to your property.
  • It can be a fire hazard if you allow it to dry out in hot weather.
  • Too much mulch can suffocate your plants
  • Loses its color over time from sun exposure.
Traditional bark mulch is being used in this garden.

Both types of mulch offer homeowners an effective method for controlling weeds in their lawns.  They both offer different levels of soil runoff and erosion protection.  Both can transform your landscape and make it more appealing and unique.

When the time comes to decide, write out what problems you need the mulch to solve, your budget, and your design preferences.  Maybe one stands out more than the other in certain areas.  Maybe you see a need for both types of mulch in different locations in your yard.

That’s the beauty of lawn care. You’re only limited by your imagination and the knowledge you choose to gain. 

7 Steps to Landscape With Rocks

Step 1: Determine How Much You Need

To calculate how much you need, multiply the length and width of the area you plan on placing the rocks to determine the square footage. Next, divide the square footage by 80.  This number represents the total tonnage of rocks needed to cover that area in 3″ of mulch (which is the appropriate depth you will need). 

For example:

  1. You measure 16′ in length and 10′ in width
  2. Multiply 10′ x 16′ and get 160 square feet of area to cover
  3. Divide 160 by 80 and get 2
  4. You will need 2 tons of rock to cover the entire area in 3″ of mulch

Step 2: Order the Material

Call your local landscape supplier and order the appropriate amount of your chosen rock type.  Have it delivered to your home whenever it fits into your schedule to coincide with the installation.

Step 3: Prepare the Area

Remove all weeds from the area by pulling them out with your hands.  Use a garden trowel for tougher weeds. It’s important to remove the weeds from the roots to the shoots.  The entire plant needs to be taken out of the ground.

Step 4: Lay Down Your Barrier

Roll a layer of landscape barrier fabric from one end of the area to the other, going 4″ beyond the edges on each end.  Cut the fabric at the 4″ mark.

Then roll back across the area, overlapping each subsequent section of fabric 4″ onto the preceding section.  This ensures that you will completely cover the ground to inhibit weeds from penetrating through to the surface.

Repeat this task until you have the entire area covered in your barrier fabric.

Step 5: Lay Down

Begin shoveling rocks onto the edge furthest away from any buildings or walls. Work across the area towards the buildings or walls until the entire area has been covered by 3″ of landscaping stones.

Rock mulch needs to be laid layer by layer.

Step 6: Smooth Out the Surface

Using a wide-toothed metal rake, smooth out the landscaped surface until it is uniform and level throughout the desired area.

Step 7: Water

Yes, you read that right.  Use a garden sprayer to rinse any dirt and dust that may have collected on the rocks resting on the surface.  This will ensure that it cools the soil from the heat of the day and it presents the rocks in the mulch in the best possible light by exposing the widest array of colors.

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About the author: Jeffrey Douglas is a horticultural hobbyist that loves everything related to plants and gardening. He specializes in gardens and houseplants.

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Catherine Keniry

Thank you that was an informative article. I have a question: if you have a garden bed that has previously been mulched with pebbles, is it possible to lay organic mulch over the top? I don’t want the pebbles anymore and want to add bark mulch, but don’t want to have to remove the pebbles. Thanks! Catherine

The Green Pinky

If you just want the mulch to be used for aesthetics without anything living growing in that area it should be fine. But wouldn’t you want to use the space to grow some plants? If that’s the case you’ll need to get rid of the pebbles.

Greg sungreen

 Significant differences between a rock and mulch were mentioned in this blog. For that purpose, this blog has been a realistic one and has clarified all the doubts. This was an excellent chance to get to know the difference.