As I’m learning more about raising plants in containers, I came across this idea of using rocks on top of the potting soil. I was curious and did my research whether doing this is beneficial to my potted plants.
You can put rocks on top of soil as mulch to regulate temperature, prevent weeds, avoid soil erosion, and splashing soil on the foliage. The rocks can be used to give an aesthetic look to the plants.
Before you start adding rocks to your potting soil, you do need to be aware of the disadvantages of doing so. I’ve also written my research on how you can use the rocks and what alternatives you have like mulch or rubber.
Can You Put Rocks on Top of Soil?
Placing rocks on top of the soil is perfectly fine. In most cases, it’s not going to harm your plants in any way. That said, there are a few pros and cons you might want to mull over before you decide to use them.
Aside from adding a decorative touch to your precious plants, rocks offer a handful of noteworthy benefits. Here are the biggest.
Low-Maintenance Weed Protection
Weeds aren’t just a problem in your garden. They can start popping up in potted plants, too.
Pesky weeds are highly opportunistic and will grow anywhere there is room. All they need is some moisture and sunlight.
Rocks can work wonders to keep weeds under control. A thick layer of rocks can block the sun from reaching the soil, thus preventing weed growth. Yet, the rocks won’t prevent water and sun from feeding the existing plant.
Keeps Digging Pests Out
If your potted plants are outdoors, you may have to deal with pests with a penchant for digging. Squirrels are notorious for hiding their cache of nuts and seeds in potting soil.
Unfortunately, this puts your plant roots at risk.
Once again, rocks come to the rescue! They create a protective barrier. Squirrels may try to dig, but they’ll stop once they realize that it’s easier to look elsewhere.
Soil Erosion Preventative
Soil erosion is something that all gardeners have to deal with. Everything from harsh winds to frequent waterings can make the topsoil disappear.
Landscapers use rocks quite often to prevent erosion on hills. The same benefits apply when you use them on your potted plants.
It might not seem like much, but even a few droplets of muddy water on the foliage of your plant can do harm.
Rocks can effectively stop splashing. They create a barrier over the soil, which keeps those unwanted pathogens away from your plant.
Reduced Fungal Growth
Speaking of fungal growth, rocks can also prevent common issues related to traditional mulch products.
Most mulches absorb water. While that’s good for keeping the soil moist, it also makes the garden a breeding ground for fungi in many climates.
They provide many similar benefits as standard mulch, but you don’t have to worry about mulch-based fungus.
Now that you know the benefits rocks provide, let’s take a look at some negative aspects worth thinking about.
No Health Benefits
The biggest disadvantage is that rocks don’t provide much health benefits for your plant. Sure, they can prevent soil erosion, reduce fungus, and block weeds. But, they will not improve the soil like organic mulch.
Over time, organic mulch decomposes. The natural decomposition process infuses the soil with nutrients that the plant will actively use to grow stronger.
Rocks don’t decompose at all, so they’re not improving the soil quality in any way.
Potential to Raise Soil Temperatures
Ever touch a rock that’s been sitting in the sun all day? Rocks absorb heat.
This added heat could raise the soil temperature beyond an acceptable range. If you do use rocks in your potted plants, make sure to keep them out of direct sunlight.
May Raise pH Level
Most of the rocks you would use for this type of application are on the alkali side of the pH scale.
As a result, rocks have the potential to raise the pH level of the soil. Many plants prefer an acidic growth environment. That’s not always the case, so make sure that you understand the pH requirements of your plants before using rocks.
What Rocks Can You Use on Top of Soil?
Thinking about topping the soil in your potted plants with some rocks? You have several different types of rocks to choose from. Here are some of our favorites!
River pebbles are a favorite among gardeners. River rocks are smooth rather than jagged. They form over time by the constant wash of a moving river.
These rocks are very small, which is why they’re classified as pebbles. There are bigger river rocks available. But, the smaller pebbles suit potted plants much better.
Like pebbles, gravel pieces are very small. Typically, gravel mixes contain a mixture of different rock fragments.
Gravel is cheap, readily available, and very versatile.
You can even use aquarium gravel to add a touch of color to your potted plants!
Lave rocks are beautiful and add some bold color to your plants. The rocks come from actual volcanic lava.
In gardening, lava rocks are perfect for succulents and other drought-resistant plants.
Unlike other rocks, lava rocks have tiny air pockets that keep the soil ventilated. So, they tend to stay much cooler.
Crushed Marble or Granite
Finally, we have crushed marble and granite.
Marble and granite chips come from the same stuff that’s on your kitchen countertops! They’re beautiful stones that have a lot of shimmer and detail.
These rocks can be sharp. They’re also known to have the biggest impact on pH levels, so exercise caution before using them.
How to Use Rocks on Top of Soil
Using rocks for your potted plants is simple. But, it’s not as easy as simply plopping the rocks down and calling it a day.
No matter what type of decorative rock you use, it’s going to behave differently than mulch. Thus, you should treat it as landscaping rocks rather than simple soil covering.
If you have a smaller pot with a simple succulent, things are going to be much easier. In this case, all you have to do is remove any weeds and debris.
Using a shovel, create a level surface on the soil. For the best results, it’s best to apply about an inch of rock material. This ensures that the soil is completely covered and secure in place.
Now, larger pots require a bit more work. You’ll need to use a geotextile fabric.
These are simple woven fabrics that help to support the weight of the rock above. They can also keep the soil intact, preventing the rocks from getting buried.
Many landscapers utilize synthetic fabrics as a final layer of protection against erosion as well.
After leveling the soil, lay sections of geotextile fabric all the way to the edges of the pot. Create cutouts for the plant stem and provide ample room for any additional growth.
Your sections should overlap about six to eight inches for maximum coverage. If you need additional security, you can use fasteners or landscaping tins.
This isn’t always necessary, as the weight of the rocks should keep the fabric down in the small area. But, you could use them if you have a particularly large planter. Just make sure to watch out for the plant roots!
Once that’s done, you can add your rocks. You don’t have to make the layer of rocks super thick. The geotextile will take care of all the drainage and protection you need.
For pots of all sizes, make sure that the rocks get as close to the stem as possible. Leaving any open soil exposed will only open yourself up to trouble.
Are There Alternatives to Use Instead Of Rocks?
Small rocks and pebbles certainly improve the look of your potted plants. But, they’re not your only options.
There are many alternatives to rocks. They provide the same benefits. But, they may also improve the soil quality in the long run.
You can’t go wrong with organic mulch. As the name would imply, this is an all-natural product that will decompose with time. When it finally does, you can enrich your soil with beneficial nutrients.
Any commercially-available organic mulch works. At your local garden center, you’re likely to find simple wood chips from cedar, pine, and cypress trees.
When you mow the lawn, you can use those clippings to improve your potted plants! Like organic mulch, grass clippings break down to improve soil quality.
But, they break down faster because the ends are already dead.
Have a pine tree on your property? If so, you probably have tons of pine needles just sitting in your yard. You can easily use them for your potted plants.
They can protect the soil. Best of all, the material doesn’t compact as it decomposes. So, the soil stays light and well-draining.
Peat moss and sphagnum moss are great alternatives to rocks.
Moss is excellent for conserving moisture. In colder climates, it can also keep soil temperatures in a good range.
Also known as Coir, coconut fiber is the stringy material that comes off of coconut husks. It’s a popular material in gardening. You can find it in the form of hanging containers, rolls, or even mulch.
Typically made out of recycled car tires, rubber mulch is a synthetic product that lasts.
While it doesn’t decompose to improve soil, you don’t have to worry about replacing it. It also doesn’t attract pests, which is a huge plus for outdoor pots.