10/10/2026
100% PUMICE vs. COMPLEX GROWING MEDIA
Do you feel annoyed when others say that plants grown in 100% pumice are not as robust as those grown in complex growing media?
I don't. Because I believe we often confuse vigorous growth with physiological robustness.
But first things first. What is robustness?
Robustness is not simply about how a plant looks. It concerns the plant's ability to maintain its physiological functions, cope with environmental stresses and recover after adverse conditions.
Cell structure, tissue integrity, water regulation, nutrient acquisition, root development, stress responses and interactions with microorganisms can all contribute to how a plant performs under different conditions.
A plant may have a beautifully developed crown and a nicely developed root system. We would describe it as vigorous. But can we judge its physiological robustness simply by looking at it?
Not necessarily.
🌞 Bits to remember: "robustness ≠ vigorous"
🧬 PLANTS ARE FAR MORE COMPLEX THAN WE SOMETIMES THINK
Plants are not simply organisms that absorb water and nutrients. They have evolved sophisticated mechanisms to sense and respond to their environment.
They respond to light, gravity, temperature, water availability and chemical signals. Their roots can alter their growth in response to water and nutrient distribution, directing their development towards more favourable conditions.
But there is another fascinating aspect of plant biology: plamts interact with other organisms.
Bacteria, fungi and other microorganisms can influence nutrient cycling, nutrient availability, root development and plant responses to environmental stress. Some of these interactions develop into highly specialised symbiotic relationships.
Could a forest ecosystem function normally without its microbial communities? Certainly not.
Can we grow plants without microorganisms? Well...to a certain degree..YES!
Modern in-vitro propagation demonstrates that plants can grow in STERILE culture on nutrient media (usually Agar), containing sugars and growth regulators (hormones), without a conventional growing substrate.
But this raises an interesting question.
Just because we can grow a plant without a natural microbial community or without a conventional substrate, does that mean we should ignore the potential benefits of the biological relationships plants have evolved over millions of years and the interaction between roots and a complex substrate?
I don't think so.
🌞 Bits to remember: "Plants are complex organisms with intricate relationships with one another and their environment."
🤔 WHAT DOES THIS MEAN FOR OUR GROWING MEDIA?
Let's consider two different approaches:
1. Growing in 100% pumice.
Pumice offers excellent aeration and drainage. It can provide a suitable physical environment for roots, and plants can grow successfully in it when watering and fertilisation are managed appropriately.
But pumice alone provides a relatively limited range of functions compared with a carefully formulated complex growing medium.
Its nutrient-retention capacity is generally limited, depending on the material's properties. Consequently, the grower must pay particular attention to nutrient supply and watering practices.
When nutrients are supplied regularly through fertilisation, plants can grow quickly and develop impressive appearances. However, fertilisation alone does not reproduce every function that a more complex growing environment may provide.
Pumice is an effective mineral component. But a mineral component is not necessarily a complete growing environment.
2. Growing in a properly formulated complex medium.
A complex growing medium can combine different mineral aggregates and suitable organic components, each contributing different physical, chemical or biological properties.
Depending on its formulation, it can provide:
* A balance between aeration, drainage and water retention.
* Different capacities for retaining and supplying nutrients.
* A wider range of chemical interactions within the root zone.
* An environment that can support diverse microbial communities.
* The potential for beneficial interactions between roots, microorganisms and the growing medium.
These functions do not automatically guarantee a healthier plant. The formulation must be appropriate for the species, and excessive organic matter or poor aeration can create problems of their own.
But when a complex medium is properly designed, it offers the opportunity to manage more than just drainage and fertiliser delivery.
It allows us to consider the root environment as a functioning system rather than simply a place to anchor the plant.
🌞 Bits to remember: "A complete growing medium cannot be achieved using a single component."
🏃♂️ IS FASTER GROWTH ALWAYS BETTER?
This is where I believe we need to change our perspective.
We often want our plants to grow quickly. We want large crowns, impressive roots and rapid development.
But fast growth does not automatically mean greater robustness.
A plant's appearance tells us something about its development, but it cannot tell us everything about its nutrient status, physiological condition or ability to tolerate stress.
Roots also adapt to their growing environment. Plants cultivated under frequent irrigation and regular fertilisation may develop differently from plants grown under other conditions.
Often, experienced growers prefer to completely remove the root system when acquiring a plant grown in 100% pumice. Due to the limitations and strict watering and fertilising regimes required when growing plants in 100% pumice, the risk of the roots failing to adapt to a different growing environment is greatly increased.
🌞 Bits to remember: "Faster is not always better."
❓️HAVE YOU EVER WONDERED WHAT HAPPENS WHEN ROOTS DIE?
They decompose within the pot, creating additional risks associated with pathogens and potentially harmful substances. This is particularly common in species that naturally recycle their roots, such as Haworthia, where new roots form while older roots die and decompose.
In the absence of beneficial microorganisms, potentially harmful microorganisms may proliferate and take advantage of the decomposing organic matter. Pathogenic fungi, bacteria and other harmful microbes may colonise the pot.
If the growing medium contains structural elements that support the development of beneficial microorganisms and is additionally inoculated with beneficial microorganisms, these can help break down dead roots, reducing the risks mentioned above and potentially converting the decomposing organic matter into nutrients that the plant can absorb and use to support healthier growth.
This is a reminder that the environment in which roots develop matters, and that successful establishment depends on more than the visual appearance of the root system.
The same applies to the plant as a whole.
🌞 Bits to remember: "A well-formulated growing media that supports a compatible microbial community may therefore offer benefits that cannot be reproduced simply by supplying mineral fertilisers."
Further down we have 4 photos:
* 1st photo shows a Haworthia offset with its root colonised by dense Hyphae (Multiple fungal filaments). This forms a barrier around the root, protecting the root against bad microorganisms and helping the plant during draught periods.
* 2nd photo showing a mature Haworthia root, with its tip covered in Mycorrhizal fungi, acting as a secondary root system. Further on how this interaction helps the plant, check photo 3 and 4.
* 3rd photo is a visual representation which shows what happens inside the media WITHOUT Mycorrhizal fungi. The "P depletion zone", or phosphorus depletion zone, is the region of soil immediately surrounding a plant root where the concentration of available phosphorus has decreased because the plant is absorbing it faster than it is being replenished. Phosphate from farther away cannot always move quickly enough to replace what has been absorbed. The root may encounter less available phosphorus near its surface EVEN WHEN the surrounding soil still contains phosphorus.
* 4th photo is a visual representation which shows what happens inside the media when Arbuscular Mycorrhizal is used. The plant root has a limited reach. Its direct phosphorus uptake depends partly on phosphate moving from the surrounding soil towards the root surface. Arbuscular mycorrhizal fungi produce fine filaments called hyphae that extend beyond the root's phosphorus depletion zone. These hyphae can:
- Explore soil beyond the region where the root has already depleted available phosphate.
- Absorb phosphate from soil pores that the root cannot directly access.
- Transport the absorbed phosphorus through the fungal network towards the root.
- Transfer phosphorus to the plant through specialised exchange interfaces associated with arbuscules INSIDE root cortical cells.
🌞 Bits to remember: "What your media holds, can make a visible difference in plant growth. Beneficial microorganisms influencing how plants access nutrients, interact with their growing environment, and develop their full potential, contributing to a plant growing robustly."
🙂 SO, WHAT ARE WE REALLY TRYING TO ACHIEVE?
A plant can grow successfully in 100% pumice. But that does not mean pumice alone provides every function that a carefully formulated complex medium can offer.
The ability to grow a plant in a particular medium does not mean that the medium provides the most complete environment for its long-term development.
This is why I believe we should look beyond growth rate and appearance.
We should consider not only what we supply to the plant, but also the environment in which its roots develop and the biological relationships that may support its growth.
After all, our plants are living organisms, not merely objects that we want to grow as quickly as possible.
Some people grow plants because they enjoy GROWING them. They experiment, question, research, challenge established methods, learn from failure, and gather knowledge to become better growers year after year. For them, the real satisfaction isn't simply watching a plant get bigger. For them, the journey is just as rewarding as the result.
Others grow plants simply because they love having them in their lives. They enjoy watching them grow, admiring their beauty and collecting different species, without necessarily wanting to get deeply involved in the science, experimentation or technical side
of cultivation.
Neither approach is wrong. Some want to understand everything about their plants; others are perfectly happy just enjoying them. And, of course, many growers fall somewhere in between.
Making a plant bigger is one thing. Understanding what makes it thrive is another.
So, when someone shows you a Haworthia that has doubled in size in a few months using 100% pumice, are you impressed enough to copy the method, or curious enough to question whether bigger automatically means better?
100% pumice or a complex growing media? Follow the method that delivers quick results, or question what else might be possible?
I'm curious to hear your arguments. What's your choice and more importantly, why? 😊
