Perlite and Vermiculite are both soil substrates which are added to potting medium to enhance the structure and characteristics. There are very common soil amendments found in every garden shop because how they are often used in the soil medium when potting plants.
Perlite and Vermiculite are very different by nature although they are both added to soil to enhance aeration. Perlite gives the soil a more porous characteristic because it does not hold a lot of water, whereas Vermiculite holds water and nutrients and releases it in a slow and controlled manner which is better for plants.
Potting mediums often come with perlite or vermiculite already mixed to suit the needs of specific plants. These mediums are often heavier than if you were to just pick up a bag of perlite or vermiculite which are significantly lighter because of how they are made.
Yes, you can use both of these soil additives to enhance soil since they both share a common trait which helps make soil more porous and airier. But these two are very different and it’s worth knowing the significance of these differences when it comes to making the best potting mix for your plants.
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Perlite Vs Vermiculite
|Soil Remedial Properties||No||Yes|
|pH Ranges||7.0 – 7.5||6.5 – 7.0|
|Retains Soil moisture and nutrients||Good||Excellent|
|Increases Soil Drainage ability||Best||Good|
|Weight||5 – 8 lbs/CuFt||5 – 10 lbs/CuFt|
|Size||0 – 8 mm||0 – 16mm|
|Contains natural Minerals||Good||Best|
|Approved for organic gardening||Yes||Yes|
|Decomposes over time||No||No|
Where do they Come From –
They are both mined products which are odorless, sterile, disease-free, insect-free, and seed-free. Neither medium will rot, deteriorate, or decompose.
Both perlite and vermiculite are made by heating earthing rocks to high temperatures of over 2000 degrees fahrenheit in mining and processing plants.
The high temperature “pops” the stone and creates a somewhat popcorn like structure in both instances.
One thing comes to mind when you hear the word popcorn. “Light” and that’s true because the resulting structure is nowhere close to the weight of the parent rock which they first started off as.
The popping effect the temperature has on the rocks expands the original layout giving the rock larger and very airy internal structure.
Perlite is mined in a number of western states including Utah and Oregon, with New Mexico being the largest perlite-producing state. Other countries that produce large amounts of crude and expanded perlite include China, Greece, Italy, Philippines, Mexico and Turkey.
Is initially mined in countries such as the United States of America, Russia, South Africa, China, and Brazil.
How are they Made –
Both perlite and Vermiculite are made by thermally expanding naturally occurring earth rocks.
Perlite comes from the thermal expansion of obsidian.
Vermiculite comes from the thermal expansion of phyllosilicate minerals.
Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated.
Since perlite comes from volcanic glass it is made up of primarily 70 % silica and other elements such as aluminium, potassium, sodium. These elements are also beneficial to plants when added to soil.
Perlite is not Styrofoam, it is actually a low density industrial product used in construction, horticulture and materials used to make filters.
Perlite has a slightly polished appearance due to the bubbles with the structure and is oftentimes mistaken for Styrofoam or even eggs in the soil because of how similar they appear.
The size of the perlite substrate varies by the product sold and is determined at the production facility as demand requires.
The normal size of perlite is 0–2 mm and 1.5–3.0 mm in diameter.
Coarse grade perlite can range between 3mm to 8mm in diameter
Vermiculite is formed by the weathering or hydrothermal alteration of biotite or phlogopite. The color of rock changes into the brownish appearance based on the heat applied and the chemicals within the furnace at the time of production.
These rocks are very common and have a gold, bronze and yellows and even black appearance and are very resistant to weathering.
Vermiculite does not come from Vermipost or Worm castings.
Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated up to temperatures exceeding 2000F.
Like perlite the sizes are determined at the production facility and are usually produced in different grades.
The size of Vermiculite can range from –
- fine being between 0 – 2 mm,
- medium being 2 mm – 4 mm
- large being 4 mm – 8 mm
- extra large 8 mm – 16 mm
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What Nutrients do they Contain –
Vermiculite provides more minerals for plants than perlite, based on lab analysis.
Because Perlite and Vermiculite parent materials are found primarily in the earth, They can contain an array of other minerals which are beneficial to plants.
These minerals are found naturally in the earth and also give the raw materials of perlite and vermiculite their characteristic appearance, weight and texture based on how they are arranged.
After production the minerals remain with the perlite and vermiculite and when added to potting soil are released over time through watering and natural degradation. The plants will therefore use these minerals for growth and fruit or flower production.
A typical analysis of perlite would reveal a composition which includes (source)
- 70–75% silicon dioxide: SiO2 and other elements such as
- aluminium oxide: Al2O3
- sodium oxide: Na2O
- potassium oxide: K2O
- iron oxide: Fe2O3
- magnesium oxide: MgO
- calcium oxide: CaO
A typical chemical analysis of commercial vermiculite shows it contains (Source)
- 38-46% silicon oxide (SiO 2 ),
- 16-35% magnesium oxide (MgO),
- 10-16% aluminum oxide (Al 2 O 3 ),
- 8-16% water,
- plus lesser amounts of several other chemicals.
Vermiculite provides more minerals for plants to use based on the above analysis since silica or silicon is an inert material meaning that it does not add any nutritional value towards plant growth.
Perlite although it does not provide as much nutrients, gives the soil a more aerated structure allowing water to drain more freely which is beneficial to many plants as we would discuss further in this article.
How Do They Influence Soil Structure –
Apart form creating a better aerated soil, vermiculite is also used in soil remediation where soil is contaminated with heavy metals. The addition of vermiculite significantly reduces the uptake of metal pollutants by plants.
This helps plant growth within contaminated soil by creating an environment for beneficial bacteria and microorganisms (bugs) to thrive.
Water Retention Ability –
Vermiculite absorbs and holds more water than Perlite.
Perlite is made through heating volcanic glass which then is puffed like popcorn. This prevents its ability to hold water within its irregular structure.
This gives perlite the ability when added to soil, to help water to drain more freely creating a less moist soil. As a result it is often used in potting mix formulated for succulents which requires a well drained soil rather than keeping it moist.
However from research, I have found that water retention can be affected by the size of the perlite substrate being used. I am also accustomed to the uniform smaller sized perlite.
As a general rule, clay-rich soils need coarse grade perlite to provide good drainage while medium grade perlite provides a balance between air and water-holding capacity. Fine grades will help with moisture retention in fast draining sandy soils. (source)
Vermiculite on the other hand has a more sheet-like structure which gives it the ability to hold more water while still keeping the soil well aerated. It provides excellent soil moisture control.
Vermiculite acts more like a sponge and expands when introduced to water to 3 to 4 times its size.
This makes vermiculite an excellent potting substrate when used to germinate seedlings as the water retention keeps the soil moist and the structure keeps it well aerated.
When pressure is applied to perlite it crushes into a dusty material whereas when pressure is applied to vermiculite it compresses like a sponge. This is a tell tale feature that shows the water retention ability of vermiculite.
What Plants are they Most Beneficial for?
|Basil, Coriander, Parsley|
Can you Mix Perlite and Vermiculite? –
Perlite and Vermiculite can be mixed together in a 50/50 ratio to create a balanced soil mixture.
Horticulturists recommend that a 1:1 ratio of vermiculture and Perlite can be mixed and then added to potting soil to give it a well balanced mix.
This would combine good water retention ability and aeration within the soil to provide the best growing condition for potted plants as a general soil mix.
When it comes to plants with specific needs the mixing ratio can be tweaked such that it will provide the right conditions for that specific plant and there is no general rule of thumb when it comes to this.
As a plant owner you would know what your plant needs after monitoring its growth and development and therefore you can create a potting mix that is well suited for your plant’s needs.
How Much do Perlite and Vermiculite Weigh?
Volcanic glass perlite and vermiculite weighs up to 40 times less than its parent material after the thermal expansion process.
Perlite weighs 5 to 8 pounds per cubic foot (80-128 kg/cubic meter) while
Vermiculture Weighs 5 to 10 pounds per cubic foot.
pH Ranges –
Perlite has a pH range between 7 – 7.5 and is relatively neutral meaning that it would not affect soil quality when mixed together.
However it has been noted that in some cases addition of perlite to potting soil, sometimes increases soil alkalinity and additional measures have to be taken to rectify the pH spike.
This can cause fluoride burns on foliage plants that prefer more acidic conditions.
Vermiculite has a pH range between 6.5 – 7.0 and has the ability to regulate pH a lot better than perlite so it actually acts as a buffer against excessive acidity or alkalinity.
This helps plants in their ability to take up and use available nutrients from the soil.
Precautions when Choosing Perlite and Vermiculite –
Perlite and vermiculite are both used in the construction industry and in this case, other chemicals are added to the perlite and vermiculite to create a substrate that suits that particular industry.
With that being said, it can contain harmful substances such as asbestos (a known carcinogen), which is why you should only purchase and use horticultural grade perlite and vermiculite for your plants.
How to Handle Perlite –
Perlite produces a lot of dust when being extracted from the packaging. Holding a piece of perlite and applying pressure would crush it into a dusty material.
It is recommended that you wear a face mask to prevent breathing in the dust particles since it can cause irritation to the nostrils and lungs.
This is because it is mainly silica based and silica has a high affinity for water, therefore it will cause dryness and irritation if inhaled.
Ability of Vermiculture and Perlite to Hold and Release nutrients
Vermiculture provides better nutrient retention and release to the plants.
Vermiculture helps hold and release liquid fertilizer more slowly similar to yellow Osmocote balls which is important when it comes to plants with nutrient deficiencies and you’re trying to correct it.
Potted plants also require fertilizer to be added on a scheduled basis and having a good mix of vermiculture in the soil could help retain and release the nutrients to the plants slowly until the next fertilizer addition is required.
This helps in keeping the plant healthy and flourishing all year round.
Perlite on the other hand would not hold nutrients but gradually leaches it out of the soil with each watering.
This reduces the ability for the plant to access and use the nutrients and would therefore lead to nutrient deficiencies as time passes.
Vermiculite Uses in the Garden –
|Add to soil for conditioning and lightening||Helps young root growth, soil aeration and soil moisture retention|
|Used as a Mulch||Apply 2 -3 inches around roses or tomatoes|
|Used as a Soil Remedial||Add to heavily leached soil or soil with metal poisoning.|
|Germination of seedlingsHelps retain moisture, allows seed to grow more rapidly Protect bulbs and RootsPlace bulbs in a container and cover with vermiculite to prevent moisture and mildewSoil conditioner Add to loamy sticky soil to help aeration|
Which Is Better Perlite or Vermiculite? –
From the results stated in the answered questions above, it shows that vermiculite is the overall winner when it comes to an overall comparison.
But the conditions required by specific plants can call for a blend of both substrates to provide the right soil mix for plants to grow.
Some plants prefer a more predominant perlite mixture for a well drained and aerated mix and others require more vermiculture in the mix.
It all comes down to the plant and its specific needs.