Pumice vs Perlite – Differences + Which to Use in Potting Mix

Pumice and perlite are commonly used in making soilless growth media in combination with other organic ingredients like coco coir or peat moss. These coarse non-toxic mineral components are also added to most potting mixes to improve drainage, aeration, and moisture retention.

Adding pumice or perlite to standard potting soil makes overwatering impossible. The porosity of the materials allows the free flow of water and air in the soil thus preventing root rot in cacti, succulents, and other plants that don’t like excess water around their roots. 

While both pumice and perlite have great porosity, each has unique characteristics that can determine their consideration. Since I always use them in amending my potting soils, let me take you through the differences between the two and my thought on which to choose.

Pumice vs perlite

Pumice is a lightweight volcanic rock that naturally forms when the lava cools and depressurizes rapidly. It has a porous honeycomb-like structure that allows water to drain through. The color of pumice might range from white to light gray to light tan depending on where it’s mined.

Perlite is artificially created by heating the obsidian rock (volcanic glass) to a high temperature that makes it expand and form a lightweight porous material. It is lighter than pumice and will likely float to the top of the potting mix when watered. The color of perlite ranges from snowy white to grayish white.

Here is a table showing the key differences between pumice and perlite.

Pumice	Perlite
It is surface-mined from naturally existing volcanic rocks.	It is created artificially by crushing and heating a volcanic glass rock.
Heavier and tends to have more water retention capacity.	Snowy white or grayish-white in color.
White to light gray in color.	Snowy white or grayish white in color.
Less available and very expensive.	More available and less expensive.

Porosity 

Pumice is more porous than perlite, with a  porosity of 80-90%. This makes it a better choice for plants that need less water around their roots. Perlite, on the other hand, has a porosity of 50-70% although it is still good enough for improving drainage in potting mixes.

Water retention

Pumice has a higher water retention capacity than perlite. It is known to hold water 1-2 times its weight. This makes pumice a better choice for plants that need to be watered frequently like tropical cacti. Perlite on the other hand can be great for plants that need sharp draining soil.

Nutrients and pH 

Pumice has a neutral pH, while perlite tends to be slightly alkaline. However, both materials do not significantly affect the pH of the soil. Additionally, perlite and pumice have no nutritional or microbial value to plants or soil.

Cost and availability

The cost of pumice and perlite can vary depending on factors such as location, availability, and the quantity purchased. However, perlite tends to be less expensive and widely available than pumice. You can check their availability at nearby garden centers, home improvement stores, or online retailers.

Which is best for you?

Pumice and perlite are both effective for improving soil drainage and airflow around the plant roots. However, your choice of one will depend on the specific needs of your plants and your personal preferences. 

If you are looking for a material with good drainage and great water-holding capacity then choose pumice. Otherwise, perlite is affordable and more available.

It is also possible to use both perlite and pumice in your potting mix to get a taste of both worlds. That is good water retention and excellent drainage.

.Here are important tips on how to use pumice or perlite in making your own potting mix.

• Use a coarse-grade type of perlite or pumice. Fine grades can wash out or clog up the drainage holes in pots and containers.
• Thoroughly rinse the perlite or pumice before using it. Make small holes in the packaging back and run water it to wash out the dust. 
• Combine the ingredients in the ratio of 1 part pumice or perlite to 2 parts potting mix to make a mix with great drainage and aeration.
• Wet the pumice or perlite before adding it to the potting mix. This will help to prevent it from floating to the top of the potting mix.
• Mix the pumice or perlite thoroughly with the potting mix. This will help to ensure that the potting mix is evenly aerated.

Final Thought

Perlite and pumice are all great for improving soil drainage and aeration. They all have great porosity and water retention. The main difference between them is how they are processed, their availability, and their cost. Perlite is widely available and less expensive but not very durable.

Pumice on the other hand is costly and less available but it is durable and more eco-friendly. Since it excellently retains moisture and improves aeration, I find it the superior choice. 

References

Soilless Growing Mediums – Oklahoma State University

Evaluating Container Substrates and Their Components, W. Garrett Owen and Roberto G. Lopez – Purdue University

Boyle, Thomas. Plant and Soil Sciences.University of Massachusetts, Amherst