Perlite vs. Vermiculite: What’s The Difference?
Trying to decide between vermiculate and perlite for your garden? It can be difficult to figure out which of these soil additives is better for your garden needs. In this article, gardening expert and former organic gardener Logan Hailey examines the differences between them, and the best uses of both.
When you’re standing at the garden store, it can be difficult to figure out what soil additive is best for your plants. You may need something that is good at retaining moisture. Or you may need something that excels at draining excess water.
Perlite and vermiculite are two of the most common ingredients in potting mixes and pre-blended garden soils. Both are expanded minerals used to improve drainage and moisture retention in potted plants or seed-starting nurseries.
However, it is a common misconception that perlite and vermiculite are the same things. There are some major differences between these two materials. This guide will help you determine whether perlite or vermiculite is better for your plants. Let’s dig into everything you need to know about perlite versus vermiculite.
- 1 Overview: Perlite vs. Vermiculite
- 2 What is Perlite?
- 3 What is Vermiculite?
- 4 Final Thoughts
Perlite vs. Vermiculite Comparison Chart
|Best for||Plants that need superb drainage such as potted houseplants, succulents, Mediterranean plants, and seeds prone to damping off||Plants that need moist or boggy soil (seed starting mix, cutting propagation, moisture-loving houseplants, and drought-prone gardens)|
|Improves||Compacted, wet, or clay soils||Loose, sandy, or dry soils|
|Function||Quick drainage and excellent aeration, plus some water holding properties||Excellent water absorption and retention with moderate aeration and nutrient holding capacity|
|Water Retention||Holds up to four times its weight in water||Holds up to 16 times its weight in water|
|Color||White||Sandy to brown|
|Size||Super coarse, coarse, medium grade, and fine grade||Large, medium, fine, superfine, and micron|
|Distribution||Tends to float to top of soil||Tends to mix evenly into soil|
|Compaction/Longevity||Resistant to compaction over long time frames||Condenses under pressure and may not maintain aeration over time|
|Plant Nutrients||Little to none||Trace potassium, magnesium and calcium; attracts and holds plant nutrients|
|pH||Almost neutral (7.0) with some buffering capacity||Almost neutral (7.0) with some buffering capacity|
|Material||Obsidian rock (volcanic glass)||Mineral (magnesium-aluminum-iron silicate)|
|Processing||High heat expansion||High heat “exfoliation”|
|Origin||Blast or open pit mining in USA, Greece, Turkey, Japan, and others||Open pit mines in USA in South Africa|
|Toxicity||Non-toxic and chemical-free||Risk that the dust may contain trace amounts of asbestos|
|Safety in the Garden||Wear a mask while mixing||Wear a mask while mixing|
|Use in Organic Gardening?||Yes, OMRI-approved||Yes, OMRI-approved|
Vermiculite and perlite are mineral soil additives that improve the porosity and water-holding capacity of the soil. Whether used in a seedling mix, potting mix, or in your garden beds, both vermiculite and perlite are mainly used for water management. In general, perlite has the best drainage enhancement while vermiculite has the best moisture retention.
Perlite’s rounded shape is what makes it so great for adding aeration and drainage to the soil. It can hold about four times its weight in water but doesn’t retain nearly as much moisture as vermiculite. Vermiculite has a flat or flaky shape that adds some drainage but tends to hold onto far more water than perlite (up to 16 times its weight).
This means that perlite would be a great option for a potted plant that is prone to root rot (for example, pothos or lavender) while vermiculite would be better for a moisture-loving crop like perennial cuttings or carrots.
Because neither of them provides a major dose of nutrients (vermiculite has some trace minerals), these amendments focus on improving soil texture rather than fertility.
Perlite is particularly advantageous for heavy clay or compacted soils. Imagine the size and shape of microscopic clay particles— they look like stacks of paper sheets that easily become concreted together.
Mixing perlite in with clay would be like introducing bowling balls to the soil texture to give more space for airflow and water drainage. Most plants, especially houseplants, benefit from well-draining soil with perlite as an additive.
On the other hand, a microscopic view of sand particles would look like a bunch of bowling balls stacked on top of each other. Water would rush through them and it would be hard for any moisture to remain in plant roots.
Adding vermiculite would be like stuffing bread crumbs between the bowling balls. It sponges up more water to help the soil stay wetter for longer. Many plants benefit from this moisture.
Particle Size Comparison
Both materials come in varying sizes that are most suitable for distinct uses. For example:
- Fine-grade perlite (1/16 to 1/128” diameter) is almost as effective as superfine vermiculite (1/25” and smaller) for rooting cuttings and starting seeds.
- Coarse perlite (3/16” to 3/64”) is great for succulents and indoor orchids.
- Medium-grade perlite (1/8” to 1/32”) is ideal for a highly porous potting mix for a lavender plant or a seed starting mix for seedlings that need lots of aeration, such as cucumbers.
- Fine and superfine horticultural grade vermiculite is great for starting seeds and cuttings that need plenty of continuous moisture.
Wait – Aren’t They The Same?
While vermiculite and perlite have some similar uses in soil mixes, they are not the same material. Perlite is best for aerating the soil and making it drain faster. Vermiculite is better for holding onto moisture and keeping soil from drying out.
Perlite comes from the high heat expansion of obsidian rock (volcanic glass), while vermiculite comes from a mined mineral (magnesium-aluminum-iron silicate) that is “exfoliated” into flakes under high heat conditions. In their purest forms, both materials are completely natural and non-toxic, however, some vermiculite has been contaminated with asbestos in the past.
Perlite is a lightweight naturally-occurring mineral used to aerate garden soil. You may recognize it as the little white balls in the potting mix. It is great for applications that need a lightweight, ultra-porous material, such as hanging planters or potted plants.
Perlite is made of crushed and heated volcanic rocks that are formed by the hydration of obsidian deep underground. Once mined, perlite is heated until it pops like popcorn. It has the unique capacity to expand to 20 times its original volume under heat, which makes the final product fairly productive at absorbing and retaining moisture.
At the same time, perlite’s extremely porous particles make it moisture-wicking to enhance the drainage of soils. Rainwater and irrigation can pass more freely through soils with perlite, which means less waterlogging or disease problems. This dual function of absorption and drainage means perlite is one of the best-known materials for growing plants in containers.
Humans likely were aware of perlite as early as the Third Century BC. However, industrial mining of perlite is a fairly recent activity that started in the 1950s. Use in agriculture is even more modern.
It is said that perlite originally got its name from its pearly or waxy luster that looks like tiny pearls. Perlite is also used industrially in making fire bricks, molten metal topping, and non-asbestos-containing insulation.
While it may look like little balls of styrofoam, perlite is a completely natural and OMRI-approved material for organic farming and gardening. It is technically a mined mineral that is heated to create expanded lightweight bubbles that hold air and water.
There are no chemicals involved in making perlite. It is simply a heated “popped” mineral. Perlite is 100% non-toxic. It does not threaten the health of humans, animals, or the environment.
Although perlite is a naturally-occurring mineral, it is technically a nonrenewable resource because the obsidian rock takes millennia to cool, hydrate, and turn to perlite in the earth. But sustainability experts say that we have only mined less than 1% of global perlite reserves.
Most of the world’s perlite mines are located in the U.S., Greece, Turkey, and Japan. The American share of perlite reserves amounts to less than 15% of global resources. The majority are located in California, Arizona, Idaho, Nevada, New Mexico, and Oregon.
While perlite is a mineral from the earth, it is not technically biodegradable. The perlite balls in the soil are made from superheated volcanic rocks that won’t decompose over time. Adding perlite to the soil permanently alters the texture and improves its capacity for growing crops.
What Are the Benefits of Perlite?
As a soil additive, perlite’s primary role is aeration. Its airy texture helps improve the drainage of potting soil and seed-starting mixes so that water flows through them more easily. This results in healthier seedlings and potted plants with a lower risk of diseases like dampening off or root rot.
Perlite is essentially “volcanic popcorn.” It starts as a form of volcanic glass called obsidian. Obsidian is an igneous rock that formed from millions of years of quick-cooling lava deep under the surface of the earth.
When water meets that volcanic glass, it becomes perlite. Geologists have found that most obsidian turns to perlite in under 20 million years, which makes this mineral surprisingly young in geological terms.
After perlite is mined from the Earth, it is rapidly heated to 1400 to 1800°F by a giant “popper.” The water contained in the perlite transforms to steam and causes each tiny “pearl” to bubble up to 20 times its original volume. The result is “expanded” perlite which is much like popcorn. It is lightweight and filled with air, ready to be added to your soil.
Is Perlite Safe to Use?
Perlite is a very safe, natural, non-toxic material that has even been added to lotions and soaps to replace plastic microbeads. It is also considered completely safe by regulatory agencies. There is some concern over the very fine dust perlite generates that could harm your airways when inhaled.
When you look at groups of people who are exposed to the largest quantities of perlite (the miners and factory workers), you can feel even safer about using perlite in your garden. Studies show that mining dust from perlite production plants does not negatively affect the respiratory health of workers in the U.S.
Some gardeners and farmers take an added precaution by wearing a mask when dealing with large amounts of perlite. The general consensus is that perlite poses no significant risk to gardeners or farmers using it in potting soil.
Nonetheless, as an asthmatic, I always recommend wearing a mask when pouring large bags of perlite. It can kick up large amounts of dust and I prefer to keep that dust out of my lungs.
According to University of California Davis, there are currently no published reports that perlite could negatively affect your health. The government agency that regulates occupational health says perlite is considered a nuisance dust.
However, they admit that excessive inhalation over long periods of time could be irritating to your lungs. Just use a scoop for small amounts or wear a mask when pouring large amounts.
Pros and Cons of Perlite
Pros of Perlite
- improves soil drainage
- Very lightweight
- Resists soil compaction
- Prevents root rot in potted plants
- Great for seed starting & houseplants
- Neutral pH
Cons of Perlite
- Does not hold as much moisture
- Water drains away very quickly
- Dust can irritate your lungs
- Can blow away in the wind
- Tends to float in excess water
- Nonrenewable resource
- No plant nutrients
Vermiculite is a naturally-occurring clay mineral that looks like glossy flakes. It is made of magnesium, aluminum, and iron silicate and ranges in color from sandy to dark gray. Vermiculite is used in seed starting mixes, potting mixes, and rooting blends for cutting. It excels at holding onto soil moisture and slightly improving drainage.
Vermiculite particles can hold up to 16 times their volume in water, which means this material expands when irrigated. Unlike perlite, vermiculite is heavy enough to stay mixed into the soil and won’t blow away or float to the surface when watered.
Another big advantage of vermiculite is its ability to hold onto soil nutrients. It has a high cation exchange capacity, which means that minerals and fertilizers “stick” to it. Vermiculite attracts positive ions like potassium, magnesium, calcium, and ammonium. On its own, it also contains trace amounts of potassium and magnesium.
Moisture-loving plants like ferns, violets, peace lilies, begonias, carrots, and other vegetables. However, drainage-loving plants like cacti and succulents do best with perlite because vermiculite holds onto too much water.
Vermiculite got its name from the Latin word “vermiculare” which means “to breed worms,” a reference to its tendency to “exfoliate” (turn into long strands) when heated.
Vermiculite is a naturally occurring mineral clay made of magnesium, aluminum, and iron silicate. Vermiculite expands when heated and is industrially processed to yield the lightweight soil additive we see in stores.
According to the United States Geological Service, vermiculite ore is primarily mined in Montana, Virginia, and South Carolina. Palabora, South Africa is the other major producer.
Vermiculite is a biodegradable clay, but it takes a long time to break down. As vermiculite decomposes, it feeds soil microorganisms and the nutrients absorbed in its microscopic clay sheets become available to plants. It also adds grit to the stomachs of worms, which can be very beneficial for your soil or compost.
What Are the Benefits Of Vermiculite?
When added to soil, vermiculite can improve the moisture retention, drainage, nutrient holding, and overall vitality of your plants. It can be added to the seed starting mix to keep seeds moist while they’re germinating. It can also be added to potting mix and compost to improve drainage and nutrient holding.
Vermiculite is great for keeping softwood cuttings moist as they root. Compared to perlite, vermiculite is a better option for moisture retention because it holds onto moisture inside its flake-shaped clay structure.
Vermiculite is derived from crystalline rocks that naturally decompose and weather over thousands of years. It is mined from the ground and then heated and expanded through a process called exfoliation.
The result is a lightweight, flaky mineral material that turns brown from the temperature of the furnace. Expanded vermiculite granules are then bagged alone or added as an ingredient in potting mixes.
Is Vermiculite Safe to Use?
Vermiculite does not pose significant dangers to home gardeners due to the small amounts found in potting soil and the tendency for vermiculite to be pre-moistened before use in the garden. Nonetheless, vermiculite can be dangerous to be inhaled.
When pure, vermiculite is a completely natural mineral that is completely safe and non-toxic. However, the historical manufacture of vermiculite (specifically for use as insulation) was contaminated with a toxin called amphibole asbestos.
In the modern day, a recent EPA study found that some vermiculite products still contain low levels of asbestos, a chemical known to cause cancer, lung disease, and breathing issues.
The big uproar against vermiculite came in the 1990s when one of the largest vermiculite mines in the world (located in Libby, Montana) was found to be contaminated with asbestos. In 2000, the EPA named the area a Superfund site and declared a public health emergency for the town of Libby.
Large volumes of vermiculite particles can irritate your nose and throat if you breathe them in. It’s best to use vermiculite outdoors in a ventilated area while wearing a mask. Vermiculite should be used while moist to ensure that dust fibers are not released into the air.
Peat moss, sawdust, or shredded bark are safer alternatives to vermiculite. These are natural alternatives that do not emit any chemicals or residue that could cause potential harm.
Pros and Cons of Vermiculite
Pros of Vermiculite
- Highest water retention
- Holds onto plant nutrients
- Contains potassium and magnesium
- Neutral pH
- Natural mineral clay
- Great for high-moisture plants
Cons of Vermiculite
- Prone to compaction
- May be contaminated
- Can have asbestos chemicals
- Not good for root rot
- Mining may impact the environment
- Less widely available than Perlite
Perlite is like mineral popcorn, while vermiculite is like a sponge. You can find perlite and vermiculite in almost every soil mix on the market. Both materials are great for adding aeration and drainage to potting soils and seed-starting mixes. They are lightweight, fluffy, and easy to use. They also both come from natural mineral resources that are approved for organic gardens.
But moisture retention is where these two products diverge. Perlite cannot hold nearly as much water as vermiculite does. Perlite improves drainage while vermiculite holds onto moisture. Vermiculite sponges up water (and nutrients!) to keep the soil moist over time. This can be great for ferns, but terrible for cacti or succulents.
Ultimately, the best material for you depends on the plants you are growing.
Choose Perlite For:
- Plants that love drainage and dryer soil
- This includes cacti, succulents, desert plants
- Starting seeds that are prone to damping off
- Rooting hardwood cuttings
- Aerating compost
- If you’re concerned about dust or chemical exposure
Choose Vermiculite For:
- Plants that need more moisture and wet soil
- This includes ferns, carrots, or micro greens
- Keeping the soil to stay continuously moist for seed germination
- Rooting softwood cuttings that can’t dry out
While there are some major differences between these two potting amendments, they both can have use in the garden. If you want the best of both worlds, you can always mix both perlite and vermiculite into your soil blends!