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Covering Potted Plant Soil with Rocks: The Benefits

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Covering topsoil with rocks comes with many benefits when done right and adds a modern look to both indoor and outdoor plants. 

Rocks can be used to cover the topsoil in potted plants because it adds to the aesthetics of the plant, prevents water loss, fungus gnats, weeds, splashing, and soil loss when the soil is being watered and pets from interacting with the soil. 

There are many different types of rocks that can be used as mulches for indoor plants but there are some things such as rock type and placement that must be considered to get the best results when using rocks on the soil of indoor plants.

We are going to discuss the benefits of using rocks as mulch and whether they should be mixed with the soil or even used as a drainage mechanism further in this article.

If you are interested in beautiful soil cover rocks that will make your plants stand out and provide a touch of modern to your living space. You can find it by clicking here.

stone mulch in potted plant (1)

Benefits of Covering Topsoil in Potted Plants with Rocks

Rocks are Used for Aesthetics

In many instances, the rocks are used for the aesthetics of the plant which gives it a certain sophisticated look to fit in with any modern decor.

The use of rocks is widely known for its decorative covering in cacti gardening.

The preferred color, in this case, is white which contrasts the greenery provided by the plant, although many other colors are used to create beautiful fairy gardens.

However, some consideration should be placed on the type of rocks that are used to cover the topsoil.

Some rocks can leach limestone which can raise the pH of the soil and harm the plant by nullifying the solubility of the nutrients for absorption by the roots.

Here are some types of rock and stones –

  • Glazed Rocks
  • Crushed Gravel
  • Brick Chips
  • Lava Rock
  • River rock

Prevents pets from interacting with the soil

The use of rocks on the soil can prevent curious pets from interacting with the soil which can cause health problems.

It is best to discourage pets from interacting or even eating potting soil. 

Potting soil is specially formulated soil that contains ingredients made for plants with specific needs when grown in pots or containers. 

The constituents of potting soil are dangerous to pets and cause a variety of ailments when ingested.

The top layer forms a barrier to the soil beneath preventing cats and dogs from playing with or even ingesting the soil.

Prevents Water Loss

Adding rocks to topsoil prevents water loss by shading the soil and reducing the temperature below it.

As a result, less water evaporates out of the atmosphere.

Additionally, the rocks prevent drafty winds from removing water out from the soil as it acts as a shield when it coats the top layer. Another type of mulch that has the same effect is tumbled glass.

Prevents Splashing and Soil Loss when Watering

Mulching with rocks will again act as a shield and break the force of irrigation on the topsoil preventing it from being splashed up onto the inner sides of the container or even onto your floors.

It may get annoying after every time when watering your potted plant for you to have to go back and clean up splashed soil afterward. 

Rocks help prevent such splashing when watering and as less water is lost to the atmosphere, the plant may also have to be watered less frequently.

Prevents Fungus Gnats

Fungus gnats are small fly-like creatures that have a similar appearance to mosquitoes. They have a short life cycle and can carry plant-eating fungi such as Phytophthora and Pythium.

Fungus gnats thrive in moist soil conditions, especially where there is an abundance of decaying vegetation and fungi, which is a typical feature of topsoil.

Adult Fungus gnats lay eggs on the top ¼ inch of topsoil, so providing a barrier to prevent gnats from reaching that top layer is key to eradicating these pests.

In this case, the topsoil is covered with a ¼ inch of sand. The sand will allow water to drain out quickly and will not mimic the environment that fungus gnats usually thrive in. 

Rocks may not be a good candidate in this fight as the spaces in between them can provide pathways for fungus gnats to access the moist soil beneath.

Prevents Weeds

Just like preventing the onset of a gnat invasion, mulching with rock will prevent weeds from growing in your potted plant.

Percentage Popularity of Why People use Rocks as Mulch

Reasons for placing rocks at the top

Disadvantages of Placing Rocks on topsoil

Rocks can heat up in the sun

If the plant is in an area that receives sunlight for a period during the day, it may run the risk of having the stone mulch being heated up.

When the stones are heated by the sun the heat can also be transferred to the plant causing plant stress.

Additionally, as the top layer of soil becomes heated the evaporation rate increases causing moisture loss from the soil.

Heavy Substrates can Compress the soil

Placing rocks on soil has its benefits but, if too much is used it can cause soil to become compressed.

A compressed soil can lead to waterlogging after watering as the soil will not allow the water to drain freely.

Additionally, with less spacing between soil particles, the soil will lose its aeration abilities, stifling the roots of oxygen which will eventually lead to the death of the plant.

Rocks are Used for AestheticsRocks can heat up in the sun
Prevents pets from interacting with the soilPrevents Weeds
Prevents Water loss
Prevents splashing and Soil Loss when watering
Prevents Fungus Gnats
Prevents Weeds

Should Rocks be Placed at the Bottom of the Plant Pot?

Rocks, when placed at the bottom of the potted plant can help with drainage.

Although most articles say that there are studies backing this claim, there is still no supporting evidence that rocks or any other substrate when placed at the bottom of the plant pot will help with drainage.

However, if you go the route of placing rocks at the bottom of the tray here’s what you should know based on research and combing through forums for the opinion of many plant owners and their experiences.

Used for Better Drainage

Placing a layer of rocks at the bottom of a plant potter before the addition of soil is widely used as a method to increase soil drainage and aeration.

What it actually does is that it limits the amount of soil that would be placed in the plant pot by creating a bottom layer.

Less soil creates less opportunity for plants to get the full amount of nutrients as if the entire pot was filled from the bottom to the top. 

Furthermore, the roots within the soil in many cases were found to have grown through and encapsulated the rocks holding the layer firmly together. 

This creates a nuisance when repotting as the roots now have to be untangled from the rocky layer before transplanting.

A simple fix to this is to get a planter with stubs at the bottom to increase its height so that water can drain out completely without pooling at the bottom.

Additionally, the plant saucer if used should be drained after watering to prevent water from pooling up inside the pot. 

Used to Prevent Soil Loss 

Plant pots often come with premade holes at the bottom for drainage. Some also come with the option to punch holes that are already pressed into the container. 

These eliminate the DIY action of drilling your own holes which may sometimes be oversized if the wrong size bit is used.

Oversized holes create the problem of soil being lost whenever the plant is watered. 

To prevent soil loss, the holes are covered with rocks which may range from a few, to cover the existing holes to an entire layer of rocks at the bottom of the plant pot.

As explained before this has its drawbacks and there are simple materials that can be used to eliminate the problem which we will discuss in the upcoming points.

This Compressed Organic Potting Soil works great for garden plants. It is cost-effective and solves most of my soil-related problems because it supplements the right nutrients.

Compressed Organic Potting Soil for Garden, Plants & Vegetables

Materials Used At the Bottom of plant pots Based on Popularity

Materials Used at the bottom of the container

Substrates that are often used

  • Clay pebbles

    Clay pebbles are known for their use in Hydroponics and Aquaponics. These pebbles can provide good drainage as they are porous and do not break down easily.
  • Rocks

    This is the go to substrate as it’s readily available and cheap. A layer of rocks can provide a good means of soil loss prevention.
  • Coffee filters

    Coffee filters can filter out the soil and only allow water to drain out of the soil and is used by many plant owners. 

    The only downside to this, is that if the drainage hole is large, over time the filter material may break down allowing the soil to escape freely.
  • Shade cloth or netting material

    I have found that this works best to cover drainage holes at the bottom of plant pots and keep the soil within the pot as it is being watered.

    It holds strong over the course of time as the material does not break down easily.
    See our the shade cloth we recommend on amazon by clicking here.

People’s Opinion on Placing Rocks at the Bottom of Plant Pots

Reasons for rocks at the bottom

Should Rocks be Mixed in With the Soil?

Rock should not be mixed in with the soil because it adds no benefit to the soil structure itself. 

It does not increase drainage or aeration nor does it add nutrients to the soil.

What the rocks actually do is that it takes up space that would have been filled with nutrient-rich soil. In fact, it robs the plant of nutrients that would have been available if there was soil instead of rocks.

The roots of the soil become entangled with the rocks which makes it a real pain when repotting the plant.

Instead use soil amendments such as perlite and vermiculite for better drainage, aeration, and the right amount of water retention.

Perlite and Vermiculite are very different by nature although they are both added to soil to enhance the aeration. 

Perlite gives the soil a more porous characteristic because it does not hold a lot of water, whereas Vermiculite holds water and nutrients and releases it in a slow and controlled manner which is better for plants.

Horticulturists recommend that a 1:1 ratio of vermiculture and Perlite can be mixed and then added to potting soil to give it a well-balanced mix.

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