You are at your favorite gardening shop aisle, and you see two bags of some stony-like material: once called vermiculite and the other one perlite. They look very similar, right? No, they are quite different and they can affect your plants significantly (and even kill them).
The main difference between perlite and vermiculite is how they affect drainage and areation in the soil. Perlite is not porous and increases drainage and areation while vermiculite is very porous and absorbs a significant amount of water per volume. Perlite is widely used in potting mix and cacti soil while vermiculite is used in very dry areas where watering is sporadic.
Which is best? As a gardener with 10+ years of experience I hardly ever used vermiculite. Perlite is quite often a way better material and helps in draining the soil and avoiding the number one problem (overwatering). This is especially true in rainy countries. What about vermiculite then? Keep reading!
Vermiculite vs Perlite in 3 Differences (with Photos)
I used to confuse them for a long while. However, they are not only different for how they look, but also on how you can use them. Use vermiculite instead of perlite, and your plants will likely suffer.
Vermiculite is a clay-based mineral (clay is a very fine and smooth medium very common on soil) forms underground and is mined mainly in Russia and Africa. This mineral, to become the vermiculite you buy, is heated up in industrial furnaces to release the water in it.
When this happens, the mineral literally pops (like popcorn) due to the water becoming a (larger in volume) gas and leaving the mineral. This will create empty pockets inside the material, making it very lightweight. When it cools down, it keeps a vermin shape (here is the name).
Perlite, different from vermiculite, is a specific type of solidified magma (high silica content), also called volcanic glass. Such raw material is turned into perlite by heating it up at more than 1500F (815C). This, in the same way as vermiculite, the water content in this rock evaporates, leaving empty pockets inside the material that will also expand becoming very lightweight.
Important to remember that are both pH neutral so this does not affect plant growth in terms of soil absorption or nutrients.
Let’s dive into the main differences you need to know that will make you save time and money
Colour, Shape, and Weight
Perlite and vermiculite are relatively easy to differentiate.
Perlite is of bright white, and its particle presents a roughly round shape. It is very airy but not porous (more on this later, as very important for your plants).
Perlite is sold in different sizes: extra coarse, coarse, medium, fine, and extra fine. The perlite you can find in the shops has a very low density (it uses a lot of space but is still very light) of around 40-120 kg/m3 (just as a comparison, water is around 1000kg/m3). Hence, perlite is lighter than water (as it tends to float on top of it, more on this later).
Vermiculite, on the other hand, presents a yellow towards gold-brownish particles. These have cylindrical shapes, they are very airy and lightweight. It has cavities as perlite, but more importantly, is porous (more on this in a particular section).
It is sold in 3 different sizes: fine, medium, and large (from 1mm to 12mm). It has a higher density than perlite (from 170 to 220kg/m3 depending on the particle size). Nonetheless, vermiculite is still lighter than water, but, due to its water-holding capability, it will not float. This is important for your use of vermiculite.
Their chemical composition, as discussed by Professor Mueena Samar and Minerals Dupre, is shown in the table below. They are both inert (do not release any substance in the soil), and their pH is generally close to neutral (very good news for the majority of plants and herbs).
The major difference, in terms of their composition, is the high percentage of Silicon in Perlite, as opposed to the high amount of magnesium in vermiculite.
Vermiculite, as a porous material, absorb and retain water. Perlite does not. Hence, plants will always have access to a water source if vermiculite is used in the soil. This is not good news as plants need breaks between watering as normally happens in nature.
This also explains why perlite will float in water while vermiculite does not.
This is something significant if you want to be successful in using perlite and vermiculite in your potting soil. Indeed, if you remember what we said before, perlite is airy but not porous, while vermiculite is airy and porous.
Vermiculite will absorb water like a sponge does through its pores. This will make the vermiculite expand up to 4 times and become muddy (if too much water is poured in) due to its “clay” origins.
Knowing this different behavior will make the difference between thriving or perishing plants.
In many years working as a gardener, I hardly saw people using vermiculite. This is because perlite is an excellent material for soil areation while vermiculite is not. When vermiculite is watered tends to collapse compacting the soil and reducing areation.
Perlite is ideal for making the amount of air reaching the roots of your plants. However, this is not the case for vermiculite. Indeed, when vermiculite is watered, tends to collapse, making the growing medium compact and reducing the airflow into the soil.
I have to say that talking with several gardeners and reading around the opinion is quite diverse and sometimes contrasting. However, something is very clear. Perlite and vermiculite cannot be interchanged due to their radically different water capability.
Let’s dive in!
Perlite should be used to increase the aeration of your potting soil. Hence, you can use perlite for:
- Old potting soil that lost its airy structure: if you have a bag of potting soil hanging around that you did not manage to use for a while. In such a case, you might notice that it lost a bit of its original structure and airiness.
- In case you are creating the potting soil yourself: as detailed in potting soil mix recipe perlite is a great addition to give structure to the soil and increase drainage capability;
How much perlite should you use in a potting mix? A good rule of thumb is one-third in volume. This will provide great areation without making the soil too light. Adding more perlite to the growing medium will make the soil close to cacti soil.
When you should never use perlite?
Perlite should never be used in very clay-based soil. Indeed, at first, it might sound like a good idea to use perlite to break the compact clay-heavy soil. However, after a while, the perlite will get pushed straight on top and it will not get back (as clay is very dense). Once on top, perlite will fly away even under a gentle breeze leaving the growing medium and making the effort vain.
Perlite is a great medium that can help with aeration and drainage. However, it is very light, and so, when water tends to float. This explains why having perlite on the surface of the soil is useless. It is not providing aeration or structure improvement as just sitting on top of your potting soil, not inside it. Moreover, its quite bright and white color, makes the potting soil looks unnatural.
When you create your potting mix with perlite, as a side suggestion, just add perlite (in a third ratio) to half of the soil, so you have the other half perlite-free. Perlite should be uniformly distributed across the soil. Then you can use such soil with perlite to fill the first bottom half of your container and the remaining perlite-free soil to fill the top part of the soil. This will provide excellent aeration for the roots of your plants and, at the same time, will keep the perlite away from the surface. Use fine or extra-fine perlite to avoid affecting the soil structure.
If you are using a standard potting mix for plants (usually perlite-free), perlite is not necessary. If you really want, add potting mix to half of the container, add 2 tablespoons of perlite, add the remaining perlite-free soil.
Any problem with using perlite? Yes, perlite does release dust that you do not want to breathe. Hence, use some kind of breath protection when handling it (even a scarf is more than enough covering your nose and mouth). It is not a problem when wet.
As strange as it might sound, I do not recommend vermiculite for grown potted herbs (or general plants). Indeed, vermiculite makes watering extremely challenging. Indeed, the claimed advantage by many of providing aeration does not stand. Indeed, once wet, vermiculite loses its structure, collapse, and become muddy and compact.
You can actually squeeze like a sponge as shown in the video below.
Vermiculite does not add any value in terms of minerals to the soil so it is not a plant nutrient. Indeed, vermiculite is made of many minerals, they are not going to be released into the soil if not in minuscule amounts, not useful for your plants
Hence, why does vermiculite exist? Well, it has lots of uses out of potting gardening, and it is excellent for those plants really thirsty that otherwise would need frequent watering. It is also used in hydroponic systems (where the soil is replaced with an inert medium like a combination of perlite and vermiculite).
The only use I see for vermiculite for more traditional indoor gardening (hydroponics is a kind of recent approach that I will experiment in the future and let you know), is for seedlings. How can you use it effectively? Keep reading to learn how to create the best seedlings conditions ever.
Seeds need air and quite often a consistently moist environment. Expert gardeners suggest half perlite and half vermiculite. Why do you need both? Because perlite will provide the aeration roots needed to develop, while vermiculite will give the long-lasting moisture (you water once and last several days), seedlings need to develop.
Moreover, this light mixture (thanks to the perlite) allows the first weak roots of the seedlings to make their way through the medium easily (compared to potential compact soil). However, here is the catch! This light medium must be replaced with good quality potting soil once the herbs start emerging from the medium.
Pro tip: many gardeners advise fertilizing seedlings. From my modest point of view, I do not agree. Indeed, seedlings have all the nutrients they need to sprout (otherwise, they will never manage to develop if every time a fertilized soil was required). This explains why a 50/50 mix of perlite and vermiculite is more than enough. Indeed, both materials do not have any organic trace on them (due to their origins, and the heating process they undergo).
If you have seedlings but do not want to bother with vermiculite and perlite why you do not give a try to Jeffy pellets, here you can find a detailed guide. Simple to use, you will not get your hand dirty and container, soil all in once for simple and effortless transplant.
Perlite and Vermiculite: Alternatives
Why should you look for alternatives? When looking for perlite or vermiculite, should you look for other options? If you want really environmentally friendly then yes. Perlite and vermiculite are finite resources. Indeed these are naturally produced materials at a very slow timescale compared to the speed by which we (humans) mine and use them. Moreover, high carbon-intensive processes are needed to produce them (heating at high temperatures).
However, the good news is that perlite and vermiculite consumption is quite low compared to the resources available. Nonetheless, if you want to be more environmentally friendly, then you should opt for something different.
Perlite can be replaced with pumice. It presents the same drainage (no water retention if not for the water that sticks on the surface) and oxygenation capability. The significant difference is the weight. Pumice is heavier. However, for me, it is an advantage. Indeed, it does not float on the soil and also helps keep the pot more stable (case of wind when you open the window).
Vermiculite, considering its high water capability, retention can be replaced with coir. This is a natural renewable material produced by the coconut manufacturing industry as a waste product (so totally green), as mentioned in this scientific publication for the curious. The main disadvantage compared to vermiculite is that, as any organic material, it tends to decompose over (relatively long) time. Some also suggest sawdust. However, I do not recommend this. Not only in the relatively dangerous in handy it (for the dust) but more importantly because you might need to add extra nitrogen to compensate for the fact that the sawdust will use it from the soil to decompose. This will make your life more complicated, so avoid it.
How To Create the Perfect Potting Soil?
Perlite is quite often a key ingredient in the perfect potting medium mix. Not only me but also many gardeners use it on a regular basis.
What do they do? Well, in general around a third of the potting mix they create is perlite, no vermiculite for herbs, and not thirsty plants. Other ingredients might be peat moss, compost, and fertilizer.
For more have a look at this DIY detailed guide below (click image). If you want an easy solution you can also have a look at my best choice for indoor potting soil in this detailed guide.
Can I reuse perlite? Yes, perlite can be cleaned and reused. Perlite is a non-organic material (rock) that hence does not decompose. It is suggested to sterilize perlite by microwaving, oven, or boiling in water.
Is vermiculite safe? Vermiculite is harmless in regular use, and no security produced is necessary when handling it according to the manufacturer’s guidance. For more detailed information check this article
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