Rocks In Plant Pots: When It Is Helpful and When Harmful

River Stones

If you start off with houseplants or gardening, you will eventually come across the method of putting rocks or layers of gravel at the bottom of a pot to create better drainage for the water. But does this really help or not? Rocks are not always helpful in plant pots!

Single rocks or edgy pebbles put over the drainage holes of a plant pot prevent the soil from falling out, washing out, and clogging up. On the contrary, creating layers of rocks, gravel, or any other material hinders water flow due to the saturated zone effect.

In this post, I will explain when rocks in plant pots are helpful and when harmful.

Why Put Rocks in a Plant Pot?

Why are rocks in plant pots a topic at all?

Sometimes rocks are used for decorative purposes such as adding a layer of pebbles on top of the soil. Pebbles or rocks as a top decorative layer on a plant pot are not the issue here.

The problematic use of rocks in plant pots concerns the bottom drainage layer which is what you will find out about by reading on. Many people put a rock or a layer of pebbles over the drainage holes at the bottom of plant pots to prevent the soil from falling out as well as from clogging up the holes.

Now, this method seems to be a bit contested among plant lovers and experts. I think there are ways of using rocks that are just fine while others can be less beneficial for your plants. Let’s see when rocks can be problematic and when not.

Why Not Use Rocks at the Bottom of the Pot: When Rocks Are Harmful

Many scientific studies have shown that when creating a drainage layer at the bottom of a plant pot, be it gravel, pebbles, or any other kind of material, this layer acts as a so-called uplifted “saturated zone”. In this saturated zone, as the water encounters a different material than the soil above it, it flows sidewards rather than being pulled downwards by gravity.

Hence, the created drainage layer does not create drainage at all. On the contrary, it simply elevates the bottom of the pot up to where the layer starts. This means that an even bigger part of the roots will be sitting in water constantly as the water doesn’t flow all the way down but rather gets hung up at the start of that particular layer.

The result of a compact drainage layer: The roots are overwatered and do not get enough aeration; the root system can rot or die off due to lack of oxygen.

Now, this issue mainly arises when one creates a whole and compact drainage layer at the bottom of the pot. You don’t get the same harmful impact from only a couple of single rocks or pebbles at the bottom of the pot. I will get to this in the next section about when rocks are helpful.

When Are Rocks at the Bottom of a Pot Helpful?

What you want to avoid is creating one compact drainage layer. But what you want to achieve is better drainage to prevent the following:

  • Soil from being overly washed out
  • Soil from falling out
  • Soil from clogging up the drainage holes over time

Depending on the size of the drainage holes, soil falling out or being washed out each time you water your plants can become an issue. Also, in any type of pot, over time the soil is pressed down onto the drainage holes and will eventually become so dense as to clog up the holes completely, creating its own saturated zone.

To prevent this from happening, it can be very helpful to put some bigger single rocks or edgy pebbles on top of the drainage holes. This way, you don’t create a layer that keeps water from flowing downwards but rather helps keep the hole open for water to flow through.

This works best if the drainage holes of the pot are a little bigger such as those of terracotta pots, or when you have a rock big enough to cover a couple of holes. Just always make sure that:

  • The rock is not flat but rather edgy
  • There are open gaps between the holes and the rocks

With this in mind, there is not much that can go wrong. In my opinion, it is always better to prevent the drainage holes from clogging up instead of doing nothing. Rocks are an easy way to achieve just that!

Do I Need to Put Rocks in the Bottom of a Pot?

It is not necessary to put rocks in the bottom of a plant pot. It is not an essential element for plant growth. As a matter of fact, it only represents one way of creating better drainage for your plants (and only if done the right way, as you now know!). Apart from drainage, there are no other beneficial effects of having rocks in plant pots.

There are plenty of other ways to create drainage which I will get to in the last section of this post.

Short Wrap-Up: No Drainage Layers, Only Single Pieces at Bottom of Pot

As a main conclusion, just bear in mind that generally, creating layers of material for drainage is counter-effective.

It is much more beneficial for the drainage effect to only place single rocks or items over the drainage holes to keep the soil from clogging up the hole and to prevent the soil from falling out. Take this along and your drainage will be just fine!

Keep in Mind: Full drainage layers of rocks or other materials are counter-effective by creating a saturated zone while single rocks or pieces help to keep good air and water flow.

What Else Can Be Put at the Bottom of a Pot?

Instead of rocks, what other materials or items can you use for extra drainage for your pot?

Here’s a list of what I usually use for my plant pots:

  • Broken pieces of old terracotta pots or ceramic dishes: This is my favorite for drainage! Did you break a plate lately or has a terracotta pot broken apart? Reuse the broken pieces for drainage at the bottom of a pot by placing one or two pieces over the drainage holes.
  • Shells or pieces of shells: Do you also have a huge collection of shells from all the beaches you’ve been on vacation? Use them just like terracotta pieces as drainage over the holes at the bottom of your pot. I usually sterilize them by pouring boiling water over them, just to make sure no bacteria from foreign soils get into your soil or even garden.
  • Expanded clay: Expanded clay can also make for a good drainage layer in the bottom of a pot.
  • Upside-down small kitchen sieves: Do you have old tea sieves or small kitchen sieves without handles? Turn them upside-down and place them over the drainage holes. Perfect!

Now, before you can put anything at the bottom of a plant pot, you need an appropriate plant pot with drainage holes. This is not rocket science but it does help to know a couple of tips before you start potting your green fellows. For more on how to create drainage with any type of pot, read on in my post answering all questions about drainage.

Related Questions

How to Water Indoor Plants?

Interestingly, the most common mistake in plant care is overwatering your indoor plants. Even though you mean your plants well and want them to be well-nourished, most plants don’t need as much water as we think.

Always check the upper layer of soil by sticking your finger in. Only water your plant if the upper layer of soil has dried out.

That is one helpful piece of advice for watering your plants. For a complete guide on how to water your plants with many more tips, please read my post linked here!

What Counts as Direct and Indirect Light?

Every plant type has its own light requirements. When buying plants, they usually come with some label or tag that specifies whether they need full sun, half shade, or only shade. Now, what do these labels really mean? And what counts as direct sunlight and what not?

Find out in my post about what counts as direct and indirect light and which spots in your home are suitable for what plant light requirements!

Recent Posts