Using Rocks at The Bottom of Plant Pots: Drainage Explained

Do Rocks Affect Soil Drainage? 

The key to preventing overwatered soil and the negative impact it can have on plants is to increase drainage in plant containers. Although adding rocks to the bottom of the pot can seem like a nice idea, it might actually be detrimental.

The saturated zone becomes close to the soil’s surface and gets to the roots when rocks are put at the bottom of a plant container. At the base of a planter, there is a saturated zone that doesn’t drain. As a result, the roots will stay damp for a long time, which will cause root rot.

Although placing rocks at the bottom of planters can have drawbacks, there are several situations in which doing so may be advantageous.

You will gain a greater grasp of the benefits of utilizing rocks in plant pots, the kinds of rocks you may use, and how to utilize them after reading this article.

When I repot my plants, I use a reasonably priced soil amendment that improves the soil and provides the optimum growing conditions. Click here to access Amazon, where you may find it.

Do Rocks Affect Soil Drainage? 

According to instructions from experts, gardeners have long added a layer of gravel before putting indoor plants in pots.

The University of Illinois, however, asserts that the presence of the saturated zone renders the notion that adding rocks to the bottom of the pot will assist drainage to be untrue.

See our article on how long the soil should stay moist after watering.

The Saturated Zone:

Let’s get right to it without going into any tedious details. Water falls through the soil as a result of gravity when it rains or while watering indoor plants.

All of the roots become wet as a result, and the extra water drains away.

Instead, water seeps through the soil but travels sideways through certain other strata, such as rocks.

It raises the saturated zone, bringing it nearer to the roots. As a result of spending too much time in this damp zone, roots are unable to exchange gases with the outside, which ultimately causes the death of the plants.

The reasonably priced Trazon Soil 3-in-1 Meter can be used to measure the soil’s pH and moisture content. It checks the pH as well as the amount of moisture and light. Clicking here will take you there!

When Would you Need Rocks at the Bottom of a Plant Pot?

Rocks at the base of the plant container can be useful in some circumstances. What are these circumstances, then? Let’s investigate.

When the Drainage Holes are Too Big

Larger than necessary holes are sometimes drilled at the base of planters, which can cause dirt to drain out of the pot anytime the plant is watered.

Additionally, rocks at the bottom of a planter will prevent additional soil washing when water runs through soil with bigger than usual drainage holes.

Depending on the soil composition, the runoff water that results from water flowing freely out of soil can occasionally emerge from the pot yellow or brown.

Although using a plant saucer can confine the debris and stop ugly floor stains, the issue will still persist.

When repotting a plant, adding rocks to the bottom of the planter will restrict the size of the drainage hole, preventing extra dirt from washing out whenever the plant is watered.

In this instance, rocks are merely used to fill in the gaps in the pot’s bottom. They do not occupy much space and have little impact on the water table’s saturation level or the amount of soil in the pot.

To Weigh Down the Pot

From this angle, it looks wise to place rocks or pebbles at the bottom of the plant container before adding soil.

Because rocks weigh a lot, having them at the bottom of a pot tends to give the plant the anchorage it needs to stay upright in strong winds.

In addition, the weight of the rocks will prevent the plant container from tipping over.

This method of using boulders is effective with taller plant pots that have a narrow base or diameter.

However, what should you do if a plant tips over? Yes, it does put the plant under stress, but the solutions in this essay can help.

You can also read our post about the advantages and disadvantages of burying stones in dirt.

What Type of Rocks Can You Use?

At the bottom of the planter, several rocks are utilized as substrate, including:

  • The surplus water can collect between lava rocks, away from the roots of the plant. They offer additional advantages by being porous, absorbing extra water, and releasing it gradually.
  • A typical kind of sedimentary carbonate rock with minerals other than calcium carbonate is limestone.
  • An original kind of sedimentary rock comprised of clay and volcanic ash is called slate-like rock.
  • Cinder Blocks are pyroclastic substances that are lava rock particles. They resemble pumice stones in every way.

Disadvantages of Putting Rocks at The Bottom of Plants Pots:

As was already mentioned above, there are some circumstances in which placing rocks at the bottom of the pot is advantageous.

Additionally, there are a few drawbacks to employing them, such as:

Less Available Soil: 

By taking up more room in the container, using rocks as plant pot bottoms restricts how much soil can be added.

The roots can absorb less nutrients when there is less soil present. In the bottom of a planter, there will be rock where there might have been dirt.

Because there is less soil available, plants have less opportunities to absorb all of the nutrients.

Furthermore, because they are inorganic and incapable of decomposing, these rocks have little nutritional value for the soil. They have no motivation to aid in the growth of the plant as a result.

Does not Increase Aeration:

Willis claims that water cannot easily travel from one layer of media to another, not even from the soil of a pot to a denser medium like gravel or rocks.

As a result, water will build up at the soil’s base until there is no room for air to circulate and the soil becomes saturated.

The roots of plants become more stressed when there is inadequate aeration, which increases the likelihood of plant illnesses and death.

Does not help Soil Moisture:

The ability of soil to store water and provide plants with essential minerals and water is one of its most critical roles in relation to plants.

Gravity and soil, which are better at retaining water than rocks or gravel, cause the water to flow toward the bottom of the container.

If you have partially filled your plant pot with rocks or pebbles, it indicates that there will be less soil added to it.

Less soil results in less water retention, which is insufficient to meet plant needs.

Do you need to dry off overwatered soil? To fast dry soil, see these 7 simple methods.

Effect on pH of the Soil:

The majority of plants and trees often prefer acidic soil for their growth. Here, the pH of the soil is in the range of 6.0 to 7.0.

In this range, it is simple for soil nutrients to separate into water and become used for plants.

It becomes more difficult to extract minerals and nutrients from the soil whenever the pH of the soil climbs above the 7.0 threshold and continues to rise (alkaline environment).

Putting rocks at the bottom of a planter can provide an alkaline environment, posing a hazard to plants by making it harder for them to get nutrients and minerals.

If this isn’t fixed right away, the plant suffers from numerous nutrient deficits that can be fatal.

How do Rocks Affect the Soil’s Water Table?

Although the soil in the container is open at the bottom, a perched water table forms there where the drainage level is present.

The water table of the soil is defined as this saturated water level. Between the saturated (where water “perches” or collects in soil) and unsaturated (where water has gone through) zones, it serves as a dividing line.

The root system of the plant can flourish in the zone of unsaturation. Regardless of the soil amount, the saturated zone’s height does not change.

This indicates that the volume of the unsaturated zone was decreased by the addition of rocks to the planter’s bottom.

Less room is available for root growth because the perched water table of wet soil without aeration rises over the stratum of rock.

In other words, placing rocks to the bottom of the pot produces the exact opposite of the drainage we desire.

Pots You Can put rocks in:

Large pots are typically advised due of their lower perched water table.

A broad, shallow container will hold water in closer proximity to the plant’s root than a taller, equivalent-sized container.

Gravity draws the water through the container and out of the drainage holes, which is the cause. The ratio of water to air in the container is influenced by its height.

See the article on putting rocks on potted plants.

How to Improve Soil Drainage

Using Soil Amendments

Although the rocks in planters may appear to be a kind of soil amendment, they do not provide all the advantages that come with applying the suggested soil supplements, such as:

  • Perlite
  • Vermiculite
  • fallen leaves
  • dated mulch
  • Bog Moss

If you choose to remove the moist, squishy soil, you might want to add a soil amendment to the subsequent potting mix to make sure the soil has adequate drainage qualities so you won’t experience the same problem again.

Soil amendments, what are they? These are chemicals that improve the soil’s drainage and aeration abilities. Perlite and vermiculite are frequently used as these additions.

The ideal potting soil, which you may use to repot the plant, can be made by adding the right amount of perlite and vermiculite to the intended soil.

You can read an article that goes into more detail about perlite and vermiculite to learn more about their characteristics and how they aid to improve soil structure.

My plants stay healthy even after repotting thanks to the Miracle-Gro Potting Mix I get from Amazon. Clicking here will take you there.

Bottom Watering Method

When placed in a watering tray, bottom watering enables plants to collect water from the bottom up through capillary action throughout the soil.

After 15 to 20 minutes, the plant is taken from the tray, and the extra water is allowed to freely drain from the soil.

Before it can receive another bottom watering, the soil is still wet for 3 to 4 days.

The ability of the soil to absorb water through upward capillary action is how bottom irrigation works.

It should be noted that not all soils will absorb water at the same pace.

The type and quantity of soil amendments, as well as the soil’s structure, affect how quickly substances are absorbed.

Drainage holes at the Side of the Pot

Making holes in a plant pot’s sidewalls helps increase plant aeration and water drainage.

At the bottom of the pot with a saucer, there should be 4–8 holes, each with a diameter of 1′′. Smaller holes ensure that less dirt is lost and that the soil continues to drain properly.

The saturation zone that exists above the pebbles can be avoided using drainage holes at the side of a pot.

By using “oeside holes,” it will be possible to keep the saturated water level with the rocks at the bottom while yet allowing water to flow out.

The saturated zone will keep the plant moist for a long time after watering since the water evaporates slowly and travels up into the soil.

It resembles a planter with a water reservoir at the base.

The length of time between waterings can be increased, which will require less of your attention.

Soil Type and Moisture Content

When it comes to water retention, the kind of soil might influence whether there are stones at the bottom.

Sandier soils are lighter than other types of soil, hence they will hold less water. In the saturation table with the stones, heavier soils (like clay soils) will hold onto more water.

Each type of soil has a different drying time. In the table below, we’ve included a few of them.

Type of SoilEquivalent Moisturepercent moisture 24 hours laterpercent moisture 48 hours later
Little Soil12.518.520.2
Middle Soil22.725.027.0
Strong Soil– empty crushed water bottles.-empty crushed water bottles.This has the benefit that the plant will retain moisture in the saturated zone for a long time after watering because the water evaporates gradually and percolates up into the soil.It is comparable to a planter that has a water reservoir at the base.

The Takeaway:

The interval between waterings can be increased, requiring less of your attention overall.

In terms of water retention, the soil type can affect whether there are stones at the bottom.

Sandier soils tend to be lighter, which means they will hold less water. In the saturation table with the stones, clay soils that are heavier will retain more water.

Different types of soil require different amounts of time to dry.

Admin and IT consultant and blogger, I love my Greenhouse and Indoor Plants