Pumice and lava rock are two names that come to mind almost immediately when you want to improve drainage in flower pots. But, how do you choose between them?
Consider looking at the properties of pumice and lava rock side by side.
- Particle size
- Heat tolerance
Let’s start comparing pumice and lava rock.
Pumice vs Lava Rock: Differences Summary
|More popular than lava rock
|Not as popular as pumice
|White, black, yellow, or brown
|Black, maroon, or brown
|Multiple sizes (small to medium)
|One size (medium)
|Subject to supply shortage
|Possibility of toxic metal presence
|Medium to low
When it comes to the best additional support for plant soil, Perlite is the most popular one. But if choosing between pumice and lava rock, pumice has a considerable lead over its competitor.
But although pumice is more popular than lava rock, it doesn’t mean that it is more available or even cheaper than lava rock! You may be shocked when you go to a gardening store and see more larva rock than pumice, not to mention the price difference as well.
Pumice is more popular in soil amendment than lava rock. However, in garden sculpting, lava rock is more popular. This puts them neck in neck and it totally depends on your specific requirements.
Pumice and lava rock each have their own distinct appearance. If you get confused between the two of them, you’ll find it easier to tell them apart after reading this.
Pumice is created when a volcano violently erupts and creates bubbles or froth in the molten. Therefore, pumice has a rough surface that is filled with air bubbles that form when the agitated molten lava cools rapidly.
Lava rock is the product of volcanic lava which runs down the volcano and cools on the land. It has fewer air spaces/pores and is not as rough in appearance and texture as pumice.
Lava rock is identifiable through the black or maroon/brown color the rocks bear. While pumice comes in an array of colors; black, gray, white, yellow, and brown.
NOTE- Both rocks are obtained and are crushed to make the small pebbles that are available for gardening use as a soil aid or even for landscaping.
3. Particle Size
Pumice and lava rocks show great differences in their particle size. Planning and thought need to be put into choosing the material with the ideal shape, size, and properties.
Pumice is available in a multitude of sizes ranging from fairly fine to coarse. This makes it a bit more versatile than lava rock since it comes with many options to suit all needs. The fine porous pumice grain makes an excellent top layer for potted plants.
Besides increasing porosity, it also makes your potted plant look more appealing!
Lava rock on the other hand is not available in as many options. You will find it in larger size compared to pumice. This makes it better inside the soil than on the surface. Placing it in your pot can help drain and create air spaces in which roots can grow.
Pumice particles vary in a multitude of sizes whereas lava rocks are available in larger sizes. If you are looking for finer particles, pumice will suffice. But, when medium-sized particles are necessary, lava rock is better.
It’s hard to pick a winner between pumice and lava rock as they are so similar when it comes to porosity.
Adding lava rock or pumice to your plant’s soil will naturally help water drain out of the flower pot faster. Thus, they help guard against the oversaturation of water in the soil portion where roots are present.
But, note that water can be retained in the pores of the rocks and this leads to the retention of a bit too much water. If the plants don’t like excess water (for example cacti or succulents) large amounts of these materials are not good.
If using these materials in soil for plants that like water, the moisture retained in the pumice/lava rock acts as a lifeline. Your pumice or lava rocks can help to gradually provide water to thirsty roots without rotting them.
Either one, pumice or lava rock will easily fulfill your garden requirements as they are equal in terms of porosity.
5. Heat Tolerance
The way a material reacts to heat is important. Some materials can absorb heat better than others. But, remember that good heat absorption also means that it will emit more heat. Depending on the season, excessive heat emission isn’t good for your plant’s roots.
Lava rock will absorb more heat and emit more heat due to fewer air pores on the surface of the rock. Also, it has a darker color than pumice which leads to greater heat absorption.
Pumice is lighter in color and doesn’t absorb as much heat as lava rock. Another reason contributing to this is the fact that pumice has a lot of air pockets which increases surface areas, letting the heat dissipate.
If you are looking for a material to keep your plant warm in winter, lava rock is best. But, in summer, to keep your plant cool, pumice is better. Lava rock absorbs and releases more heat than pumice.
The availability of these soil aid materials does also influence their price. The process required to prepare them for sale and use is another factor that influences their availability and price.
You would think that since both lava rock and pumice arise from volcanic activity both would feature the same availability. This is incorrect! Lava rock is much easier to source than pumice, meaning transportation is cheaper.
Pumice is not as easily available as lava rock, usually, it requires a lot of transportation to source it from the original site to distributors and finally your local department store.
Lava rock is easier to source and transport costs are minimal while pumice is not easier to the source. Meaning lava rock is easily available while pumice is subject to availability problems that can fluctuate based on supply and demand.
Can’t get Perlite or Pumice? Check these 15 Substitutes for Perlite & Pumice
The last thing you would want is to plant your plants in a pot full of toxic material. The end result would be a plant with deteriorating health that will eventually die! Hence, checking the toxicity of everything added to the soil is vital.
Pumice is non-toxic and won’t release any chemicals or gasses which may affect your plants. This is important as using the wrong material to amend your soil could end up killing your plants.
Generally, pumice is inert and does not display any toxicity. Your plants will not be affected by pumice even when it is present in large amounts in the soil.
Lava rock can be toxic as it can contain varying amounts of toxic metals such as Arsenic, Cadmium, Lead, and Barium. It is important to check the lava rock you are getting is weathered and treated to prevent toxicity.
Pumice lacks any toxicity while some lava rocks that are unweathered can be toxic as they have small amounts of toxic metals.
While both are good and restore drainage to your potted plants. Pumice has excellent draining capabilities. Meanwhile, lava rock offers medium drainage. It actually offers another property, it does well to drain soil but also helps to maintain decent soil moisture.
That said, pumice offers better drainage than lava rock.
Which one is cheaper pumice or lava rock? This becomes an important question when you need a large amount of porous material.
Lava rock is found in a lot of normal places, in almost every country. You can find it lining beach coasts, on mountains, and at their base. This makes their presence more widespread and availability much better than pumice.
Pumice isn’t as widespread as lava rock, especially since it is created by a different process than lava rock. Thus, it is not as easily available and requires transportation from countries or areas that are rich in pumice.
Taking the above points into consideration: lava rock is medium to low costing while pumice is high costing.
When it’s the competition of Pumice vs Lava rock, there is one that will pip the other one slightly. But, how do you decide?
You can decide between Pumice vs Lava rock based on characteristics like Popularity, Appearance, Particle size, Porosity, Heat tolerance, Availability, Toxicity, Drainage, and Price.
If you wish to improve drainage and soil air spaces, either of these two materials will do the job equally well. However, if cost and availability are a problem, lava rock is the better option.