For decades, a debate has ensued over which possesses the biggest benefit to our plants and propagating activities. Vermiculite vs perlite. If we step outside the paradigm of that debate, we’ll see that it’s all pretty moot.
The familiar phrase “comparing apples to oranges” is appropriate here. Because vermiculite and perlite are similar (in appearance and areas of application), but not the same.
Vermiculite Vs Perlite
To start with, perlite derives from volcanic glass, where vermiculite is what remains after certain minerals decompose. Among other distinct differences, these two soil additives actually serve two equally distinct purposes. And are therefore not interchangeable.
Let’s get straight to looking at some of the advantages of each material and its applications with regard to horticultural use. Then we will look in great detail at each material and its origin and broader application.
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Advantages of Perlite
- Increases aeration and drainage in potted plants and raised beds.
- In hydroponic systems, perlite captures air molecules, maintaining proper oxygenation for plant roots.
- Perlite is light and airy and contains tiny tunnels through which moisture can travel and drain out, protecting seedlings and cuttings from rot.
- The expanding nature of perlite works to break up dense, clay or compacted soil.
- It has an unlimited shelf life and it won’t attract bugs or mold.
Advantages of Vermiculite
- Expands up to 4 times its volume in water and retains it long enough to benefit most plants.
- Vermiculite is naturally sterile and inert and won’t harbor disease, fungi, or algae.
- Vermiculite adds beneficial magnesium, potassium, and trace amounts of other minerals to the soil.
- Vermiculite works to increase moisture and nutrient availability, cutting down on inevitable leaching.
- Useful when propagating or potting houseplants and ornamentals that prefer consistently moist soil.
So from a top-level perspective, we can see in gardening and horticulture the materials have different properties and should be used appropriately and not as alternatives to one another. That’s not to say they cannot or should not be used together as part of a potting mix or raised bed soil mix.
What is Vermiculite?
When, in nature, minerals like biotite and phlogopite are exposed to water, they begin to decompose. Once the decomposition of these minerals is complete, the material that remains is raw vermiculite or magnesium-aluminum-iron silicate.
Due to random and variable chemical reactions during decomposition, harvested vermiculite can result in a range of brown or tan hues.
Its claim to fame is its ability to expand (3 to 4 times its volume) when exposed to moisture and retain it long enough to benefit most plants. Vermiculite is also naturally sterile and will not harbor disease, fungi, or algae.
How is Vermiculite Made
Before we can use this raw form of vermiculite in our gardening practices, it must first go through a process called exfoliation. Each harvested piece is heated to between 1,000 and 1,500°F (540 – 810°C).
Exposure to this immense amount of heat causes the raw vermiculite to expand and separate into hundreds of thin layers or plates.
Once cooled, this new form is broken down into small, pebble-like shapes that will not decompose or mold and are sterile and non-toxic.
How to Use Vermiculite in the Garden
Vermiculite pellets can absorb up to four times their weight in water. They can also keep certain nutrient molecules from leaching out, via molecular attraction.
Vermiculite may initially help break up dense soil. But, over time, compaction will still occur. This is far more useful in increasing moisture retention in sandy soils.
Once processed, vermiculite is no longer considered “natural”. It won’t decompose or increase soil fertility as the organic matter will. For this reason, it shouldn’t be added to the ground soil.
Potting Mix and Raised Beds
For plants that prefer moist soil, your growing medium, in containers and raised beds, can be up to ⅓ vermiculite.
This water-retaining material is also effective for seed starting. However, I wouldn’t recommend using it for propagation. Cuttings tend to rot in soggy soil.
Water Retention
When included in your potting soil mix, vermiculite works to increase moisture and nutrient availability (far better than perlite), cutting down on inevitable leaching. Prolonged access to water and nutrients results in healthier and more robust plants. As well as an elevated resistance to pests and disease.
Moisture Absorption
Vermiculite’s proficiency, in increasing and maintaining moisture availability for plants, derives from its natural ability to absorb water three to four times its own weight. This feature is particularly useful when propagating and potting houseplants and ornamentals that prefer consistently moist soil such as ferns and other tropicals.
Rooting Cuttings
For plants that prefer to dry out in between waterings, vermiculite may cause the soil to stay too wet for too long. Propagating these in vermiculite-based soil could result in stem rot and propagation failure. Adding a bit of perlite (to increase drainage) would increase rooting success.
Vermiculite Effect on Soil pH
Vermiculite has been touted as being pH neutral for decades. When, in fact, it can have a pH level between 6.5 to 9.5. Which can be problematic when used for plants with heightened pH sensitivities.
Each batch mined and bagged will be slightly different in terms of water retaining abilities and pH. However, once the pH of the vermiculite you use is determined, simple alterations in your soil composition can be made to negate the effects of a higher pH, if present.
Vermiculite Cost
On average, vermiculite often comes at a higher shelf price than perlite, simply because mining and processing it, for gardening purposes, is more labor-intensive than perlite. The farther you are from the source, the transportation costs may also be factored in.
However, its reputation for improving potting soil and nurturing healthy plants is often quoted as being excellent value for money. Cost may also vary based on where you buy it and when. Peak season typically wields higher prices. Conversely, good deals can usually be found end-of-season.
What is Perlite?
As volcanic lava cools, it becomes a smooth, glossy, black rock called obsidian. This igneous rock is rich in oxygen, aluminum, and potassium.
In nature, when obsidian is exposed to water and volcanic temperatures, captured water molecules vaporize, causing the obsidian to expand and perlite ore is formed.
Best known for its ability to aerate the soil and allow for proper drainage, perlite loosens dense soil, contributing to the creation of a loose and loamy growing medium. Which is more conducive to growing healthy plants.
How is perlite made
Perlite is currently mined in 35 countries and processed all over the world. In these factories, crude perlite ore is crushed, dehydrated of excess water, and ground down, in a tumbler, into small pellets. Which are then shipped to “expansion” plants.
Here, industrial furnaces are heated to 871°C (1600°F). Perlite ore pellets are then run through, where the remaining water molecules, in each pellet, cause them to “pop”, just like popcorn.
How to use perlite in the garden
Perlite is a natural choice for increasing aeration and drainage in potted plants and raised beds. But I wouldn’t recommend mixing it into ground soil.
Cheaper materials, like sand and compost, that provide the same benefits, should be used instead.
Perlite, once processed, is not considered organic because it doesn’t biodegrade. Pellets can wash away with rain or excess watering and collect in areas where it doesn’t benefit.
Potting Mix and Raised Beds
For clay or otherwise dense soil in raised beds, work a 2” layer of perlite into the top 6-12” of soil.
For moisture-sensitive, potted plants, perlite should make up one-quarter of the soil composition. For plants that require more moisture, vermiculite should be used, instead.
Improve Drainage
Expanded perlite is inherently light and airy (creating negative space in soil) and contains an intricate maze of tiny tunnels through which water can travel and drain out. Without this feature, dense soil will trap water and establish a soggy environment that can rot roots and kill plants.
Soil Aeration
Negative spaces in the soil are filled with oxygen that can revitalize tired plants and critical, internal processes that encourage healthy growth.
The expanding nature of perlite works to break up dense, clay soil. Or, fertile soil, in pots and raised beds, that may have become compacted over time.
Sowing Seeds
Seedling roots are highly sensitive to soggy soil. Perlite retains enough moisture to keep them hydrated while providing adequate drainage.
25-50% perlite in the seed starting mix will contribute to a supportive growing environment. As well as providing access to sunlight for those seeds that require it for germination.
Rooting Cuttings
The same applies to propagation. Perlite is an important component of this practice. Stem rot, from insufficient drainage, is the most common cause of soil propagation failure.
Cuttings can be rooted in perlite alone, provided that the pellets are well watered prior to adding your cuttings.
Can I Use Perlite Instead Of Vermiculite?
When it comes to vermiculite vs perlite, they have similar properties but are not interchangeable.
Vermiculite can absorb 3-4 times its weight in water. This is really beneficial for mature plants in pots, hanging baskets, and raised beds. Yet, maybe too much for new seedlings and cuttings.
Perlite’s ability to aerate and provide adequate drainage is more appropriate, here. Vermiculite doesn’t necessarily loosen dense soil as well as perlite does, either.
Does Perlite Hold Water?
As opposed to “spongy” vermiculite, perlite is made up of lots of little crevices where water can collect and remain for plant access. Combined, these pellets are capable of retaining 10-20% more water than soil without it.
Just enough water to support seedlings, propagation cuttings, and plants that are moisture sensitive. Like, cacti and succulents.
Yet, they don’t provide quite enough for moisture-loving plants, like ferns, canna lilies, and other tropicals.
Does Perlite Breakdown Over Time?
Perlite doesn’t decompose over time. Once added to your soil, its composition is permanently changed. Another reason why I don’t recommend adding it to ground soil. Once added, you can’t get it out.
But, it’s highly effective for use in containers. So, if you find a deal on a giant bag of it, go for it! It will have an unlimited shelf life and it won’t attract bugs or mold.
Perlite Effect on Soil pH
The preferred pH range of most plants is between 5.5 and 7.0. Perlite possesses an inherent pH of 7.0 to 7.5.
This is important to note because a high pH can block nutrient absorption. High levels can also cause fluoride burn (commonly added to tap water) with acid-loving plants.
The amount of perlite you add to your soil should take the plant’s pH preference into consideration so always conduct a test using a soil test kit before applying.
Perlite Cost
Cheaper than vermiculite, the price of perlite still reflects harvesting, processing, and transportation costs. Prices also fluctuate due to availability. Volcanoes don’t erupt every day.
For this reason, artificial perlite has been developed and has been shown to be very similar (yet not exact) in properties.
As with vermiculite, the cost may also vary based on where available and when. Peak season typically wields higher prices. Conversely, good deals can usually be found end-of-season.
Perlite Vs Vermiculite in Industry
It’s not just gardeners who use perlite and vermiculite. They have many other industrial applications, from horticulture, right through to fireproofing, biotech, and aquatics. So let’s take a look at some of the other uses of these versatile materials.
What Else is Vermiculite Used For?
Most people are familiar with vermiculite as an effective soil additive for plants. However, it’s proven to be quite versatile, being utilized in a number of different industrial applications.
Did you know that vermiculite is also a reliable element in product safety? Making things we use every day non-combustible and non-flammable?
It’s used in construction materials to make homes and commercial buildings safer and more durable. Vermiculite’s water retention properties make it also highly prized for use in roofing, flooring, and insulation products.
Horticultural
In small doses, vermiculite actually adds beneficial magnesium, potassium, and trace amounts of other minerals to the soil.
The air to water ratio present in vermiculite stimulates root growth and facilitates the production of healthy seedlings. And can help to loosen dense, clay soil in containers and raised beds.
Fireproofing
Non-combustible and non-flammable, vermiculite is effective in lightening the weight of concrete countertops and floor tiles in kitchens. And is popular in drywall manufacturing.
Vermiculite is also a cost-effective choice for manufacturers. Savings are passed down to consumers. Making construction materials far more attainable in the marketplace.
Industrial
Thermal resistance and sound absorption properties make vermiculite indispensable in manufacturing car brakes, clutch linings, gaskets, and rubber seals.
Decades ago, asbestos was used for these. Today, vermiculite is used as a much safer alternative. Commercial vermiculite was once combined with asbestos. But, that practice stopped in the 1980s.
What Else is perlite used for?
Gardeners are familiar with perlite, like vermiculite, as an effective soil enhancer. Yet, it too has shown to be effective in other areas of science and technology. Including more sustainable ways of raising crops and livestock.
Perlite is also used in manufacturing lightweight aggregates for use in construction. Such as insulation, outdoor decking materials, decorative stone, and tile products for kitchens and bathrooms. As well as pottery and applique molding.
Horticultural
Perlite has a capacity for moisture retention. But, unlike vermiculite, it’s primarily used to increase soil aeration and drainage. Perfect for seedlings and cuttings.
In hydroponic systems, perlite captures air molecules, maintaining proper oxygenation for plant roots. Cacti and succulents also benefit from much of their soil being perlite.
Aquatics
Perlite-based concrete, in pools, considerably reduces heat loss. Keeping your pool warm for longer and reducing heating costs.
Sterile and inert, perlite filters are used to filter beverage and pharmaceutical liquids. I use a perlite filtration system in my aquarium to keep the water clear and prevent algae blooms.
Biotech
Perlite’s unique features make it a reliable resource in the development of new pharmaceuticals. Crushed perlite particles create a labyrinth of pathways that can capture and filter out the tiniest contaminants.
Perlite cakes remain porous, hold their shape well, and are versatile enough for use on most standard equipment.
Cosmetics
Perlite’s limited ability to absorb moisture makes it a commonly used ingredient in cosmetics. Face powders, concealers, and foundations often utilize perlite powder as a means to soak up moisture without disturbing the skin’s ability to breathe. Contributing to the coveted matte effect and the reduction of oily skin.
Vermiculite vs Perlite: Verdict
As far as that old debate over vermiculite vs perlite, as we’ve seen, there are significant differences. How both forms in nature, their inherent characteristics, and how they’re mined and processed, all display the uniqueness of each material.
We’ve also seen how important it is to match the right material to the right gardening activity for optimum benefit. There are clear advantages and disadvantages for the use of each when measured against different gardening projects and tasks.
Where to Buy Perlite and Vermiculite
Perlite and vermiculite are available at most garden nurseries and home improvement stores, in a variety of bag sizes and quantities. But why leave the house? Here are a couple of likes to get you straight to the best places to buy perlite and vermiculite at a sensible price for use in your garden.
