Last Updated on October 31, 2021 by Phil
Perlite vs. vermiculite, what is the difference?
I still remember the two very well because it was one of the very first lessons I learned in gardening. Surprisingly, it came from the advice of the person on the counter at my local garden center.
I remember him saying that both perlite and vermiculite were the same and that customers were using one in place of the other. So on his advice, I took home a bag of vermiculite and used it for my potting soil in place of perlite.
What happened next was not good.
In this article, I’ll explain both perlite and vermiculite as well as their similarities and differences. Just as importantly, I’ll go through when to use perlite and when to apply vermiculite.
What is Perlite?
Perlite is created from volcanic rock that has been heated under very high temperatures.
As the temperature goes up, the material expands until it pops (much like popcorn in the microwave does). And, what you end up are small, white-colored, styrofoam looking pebbles that are light in weight.
The uneven outer texture allows it to hold on to moisture (3 to 4 times its weight). And more importantly, shed this moisture much easily (and quickly) than other substrates including vermiculite.
Perlite is often used in gardening as an ingredient when creating potting soil as well as a soil amendment. It has pH between 6.6 to 7.5 (neutral) and helps with water retention and drainage.
One of the reasons it works well for growing plants is that it is lightweight, non-toxic and sterile. Thus, it will not introduce pathogens, weed seeds or soil-borne diseases.
In stores, you’ll likely see them sold in bags. Although there are larger sizes available as well.
You’ll also notice that there are different grades of perlite ranging from super coarse to fine grade. The coarser the grade, the larger the granules are more porous. Thus, they will drain moisture faster.
On the other hand, fine perlite works well for seedlings. But, it can easily be blown away by the wind because of its small and lightweight nature. Additionally, finer grade perlite is more likely to produce dust when you mix so you want to protect your eyes, nose and mouth when doing so.
What is Vermiculite?
Vermiculite is made from magnesium iron aluminum silicate minerals that are heated to very high temperatures.
During this process, the minerals expand to many times their original volume resulting in brown colored pebbles that look like unrefined brown sugar from afar.
Like perlite, you’ll see different grades of vermiculite available in stores as well ranging from the super coarse to fine granules.
Vermiculite is useful in gardening because of its ability to hold in water much like a sponge. It also retains nutrients. Both of these features help keep the roots of plants hydrated and well nourished.
Because of this feature it is best used for water-loving plants or those that like moist conditions.
Like perlite, it is non-toxic, sterile and odorless. It is likewise easily mixed with soil and other substrates to create potting mixes.
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Common Traits of Perlite and Vermiculite
Before I go into the differences between perlite and vermiculate with regards to their characteristics and how they’re used in the garden, I think it is a good idea to point out their similarities first.
This way, you get a more complete picture of both medium.
Both perlite and vermiculite are ingredients used for soilless potting mixes. They can likewise be used as soil amendments to improve garden soil should the need arise.
The two are likewise lightweight, don’t have any odor and have been sterilized before packaging. As such, you don’t have to worry about diseases, pathogens or weed seeds.
Perlite and vermiculite don’t have any smell. But, their small particles can produce nuisance dust which I’ll talk about below in the safety section.
Just as importantly, these two substrates don’t decompose or degrade. This makes them perfect for plants that don’t need to be repotting often because one application will last for a very long time.
When it comes to function, small size of the two along with their physical structures help improve air circulation.
You can use either for potted plants, seed germination, hydroponics, propagation and even transplanting.
Differences Between Perlite and Vermiculite
From above, it is easy to tell why some people will use perlite as an alternative to vermiculite or vice versa.
In addition to improving aeration, the two also help increase drainage, moisture retention and prevent soil from getting compacted over time.
However, they do so in different ways.
As such, plants that enjoy more water or consistently moist conditions do better in perlite because vermiculite tends to absorb and hold on to more water than perlite.
Thus, perlite is less suitable for these plants because it will cause the soil to dry out too quickly. This means you either need to keep watering the plant more than you normally would or the plant will likely get dehydrated somewhere along the way.
For this reason, perlite is perfect for plants that need well-draining soil. That is, plants that don’t like too much water and prefer quick drying conditions. Most tropical plants fall under this category, which is why many houseplant potting mixed use perlite. Similarly, epiphytes, cacti and succulents are also like this.
If you use vermiculite in place of perlite with these plants, the soil will likely hold too much water which will eventually lead to root rot.
Perlite vs. Vermiculite: How Do You Know Which One to Use in The Garden?
The main reason why perlite and vermiculite do the same thing but have different effects lies in their structure. As such, they both hold water, drain excess moisture and prevent soil compacting.
But. Because vermiculite is less porous and can be compressed more than perlite, it ends up retaining more water. You can think of vermiculite more like a sponge which soaks up liquid and keeps it in.
On the other hand, the structure of perlite allows it to store water on its exterior (instead of soaking things in). it has small bumps and spaces that allow for this on its surface.
Since the water stays on the outside, the extra moisture easily slides off as well. Thus, making it drain better than vermiculite.
Knowing this, I’ll now explain the when to use perlite and vermiculite. If you prefer watching videos explainers rather than reading, here’s a great video tutorial on perlite vs. vermiculite.
In short, here’s when to use perlite and vermiculite.
Use Perlite If:
- You want to improve drainage – perlite is commonly used for plants that need well-draining soil. Thus, you can use it in combination with other media to improve drainage to avoid plants’ roots from sitting in water for long periods of time.
- Your plants like staying on the drier side – for the plants like drier conditions or soil that will dry out faster, perlite is a good choice as it helps prevent waterlogging and potential problems like root rot and fungal disease. This includes plants like succulents and cacti.
- You have dense soil or clay soil – perlite is also a good option for improving heavy soils including clay so that they don’t compact over time. This will allow the roots to get access to water as well as air.
- It rains a lot, you live in a wet region or have humid climate – if where you live provides more moisture than normal perlite will help drain that extra moisture. Areas where it rains a lot or is humid will cause excess moisture that can be problematic to plants that prefer drier conditions.
Use Vermiculite If:
- Your plants like moist conditions – vermiculite tends to hold water like a sponge does. This makes it perfect for plants that don’t like soil that dried out. It will likewise make up for lack of watering by releasing the excess moisture once the soil starts to dry.
- You’re starting seeds – during germination, seeds need moisture to keep them from drying out. As such, vermiculite is a better option than perlite which does the opposite and drain the moisture faster.
- You live in a dry climate – to prevent plants from loosing too much water quickly in dry climates you can use vermiculite to help it retain moisture.
- The plants are grown in containers outdoors – in general container plants need more water because of the limited amount of soil. Additionally, growing them outdoors increases evaporation because of the sun and other elements. Thus, using vermiculite will help keep the plants hydrated.
Can You Mix Perlite and Vermiculite?
Yes. Technically, you can mix any substrate together to create a potting mix.
The important thing is that recipe will achieve its purpose, which is to give the plant a friendly environment to grow in.
That said, in most cases you won’t be using perlite and vermiculite together. That’s because each of them functions in a different way.
Perlite works best for tropical plants, epiphytes, cacti and succulents that prefer drier environments or one where there is good moisture drainage.
On the other hand, vermiculite works better for plants whose roots like to have moisture readily available to it.
But, like all things, there are situations where the two can work together.
One is for seed starting. Another is for certain potting soils.
Perlite can provide the drainage and aeration while vermiculite works to help retain moisture. While the two may look like they are in conflict with one another, mixing them can provide the right balance where the soil is able to retain enough water to keep the plant’s roots hydrated while preventing waterlogging.
Many plants like this kind of environment.
Are Vermiculite and Perlite Safe?
Perlite and vermiculite are both made up tiny particles. As such, the finer the granules, the higher the possibility you’ll experience perlite or vermiculite dust. Basically, this is the dust the puff up when you’re mixing the substrates.
More importantly, these are considered “nuisance dust” which can cause irritation to your respiratory system. While they are not cancerous and not considered hazardous, you want to be aware of it and try to avoid breathing in a lot of it.
As such, if you’re starting out with these potting media or are sensitive to dust particles, I highly suggest wearing face mask or dust make which covers you nose and mouth. Additionally, put on some safety glasses as well to keep the dust from getting into your eyes.
Both perlite and vermiculite are commonly used substrates in creating potting soil. And while some potting mix recipes will tell you that you can use one in substitute for the other, it is worth nothing that the two media are not identical.
Both don’t work on their own. Instead they need to be mixed in with other substrates.
Use perlite if you want to improve drainage or increase aeration. On the other hand, use vermiculite if you’re want to improve the soil’s water retention ability.