Perlite vs. Vermiculite: How and Why to Use Them (2024)

Back when I was new to gardening (green, you might say), I walked into a plant nursery looking for perlite, as I’d run out of it for my DIY potting mix.

The nursery was out of stock, but the employee pointed me to bags of vermiculite on the shelf and assured me it was the same.

“This is what we use in our greenhouse. It works the same way perlite does,” he promised. “You can use it in your potting mix.”

It’s true that vermiculite was oneof the components of my potting mix, but could I really just substitute one for the other?

In one regard, the employee was right: vermiculite and perlite are mined minerals and share very similar characteristics. Heck, even their names sound like they could be related.

But in another regard, the employee was off base. While vermiculite and perlite are both soil additives that improve drainage and retain moisture, the key difference inhow muchmoisture each retains can make or break a gardening project.

Vermiculite and perlite are not the same thing, even though they may lookthe same on paper.

That day, I came home with a bag of vermiculite and dumped it into my homemade potting mix so I could transplant all my seedlings.

Related: How to Repot Tomato Seedlings

Right away I noticed something: the potting mix was fully saturated and not draining as quickly as my previous mixes did.

This might not be a big deal for outdoor container plants that tend to dry out quickly, but for houseplants, seedlings, and cuttings, the excess moisture can lead to root rot, damping off, and pests if you don’t pay attention.

Here’s what you need to know so you don’t make this mistake.

What is perlite?

Nicknamed “volcanic popcorn,” perlite is made by heating volcanic glass to super high temperatures until it expands and “pops” into the white, porous, lightweight rock that resembles little Styrofoam balls.

(Despite similarities in appearance, Styrofoam should neverbe used in gardens or as a substitute for perlite.)

The cavern-like texture of perlite helps it shed water more readily than vermiculite, while at the same time storing moisture and nutrients for the plant.

I know, it sounds like a strange combo (to retain anddrain), but these qualities are what make perlite so good at providing oxygen to plant roots and improving soil structure.

What is vermiculite?

Like perlite, vermiculite is a naturally occurring mineral that expands when heated.

Scientifically speaking, it’s the name for a group of hydrated magnesium iron aluminum silicate minerals (phyllosilicates) that look like shiny, silvery gold to grayish brown flakes.

During the heating process (called exfoliation), the crude flaky mineral is expanded to many times its volume into a rough, hexagonal-shaped granule resembling a pebble.

These chunky granules are further processed into the coarse, medium, and fine grades of vermiculite that we see and know in gardening.

Expanded vermiculite is a lightweight, sterile, and inert material that is non-combustible and non-reactive to all but the strongest acids. It’s also non-toxic and safe to use in a variety of applications.

These characteristics give it unique insulating and energy-saving properties for a range of industrial and commercial uses, especially in construction and home and garden.

Vermiculite is used for special coatings and packaging, fire protection, loose-fill insulation, concrete screeds and plasters, swimming pool liners, and potting mixes or potting soils. It’s the same material used in gas fireplaces with ceramic logs to help the flame spread across the burner more evenly.

Does vermiculite contain asbestos?

The short answer: no.

If you’re buying horticultural vermiculite sold in stores today, then that vermiculite does notcontain asbestos and is not dangerous for your garden. (Though it’s recommended to wear a dust mask when handling large amounts of vermiculite, due to the fine particles.)

At one time, however, vermiculite did have asbestos, and it may still exist in places like the attic insulation of older homes.

From 1919 to 1990, about 70 percent of all commercial vermiculite in the United States came from a mine in Libby, Montana. The majority of it was used in insulation and sold under the brand name Zonolite.

The vermiculite from the Libby mine contained a naturally occurring asbestos calledtremolite-actinolite. After it was discovered, the mine shut down.

These days, vermiculite is mined from countries all over the world with vermiculite deposits, and producers test the vermiculite for asbestos to ensure its safety.

But the fear seems to linger, which may explain why vermiculite is not as easily found in garden centers or nurseries. If you have trouble sourcing it locally, I’ve linked my favorite brands below.

Perlite vs. vermiculite: how do you know which one to use in the garden?

Like perlite, vermiculite is an effective soil conditioner that can loosen compacted soil, provide drainage, and hold three to four times its weight in water.

But—and this is an important but—vermiculite is more compressible and lessporous than perlite, giving vermiculite higher water-holding capacity when it’s used as a planting medium.

Vermiculite acts more like a sponge in the way it soaks up water and holds on to it. Perlite stores water on the surface of all its nooks and crannies, which is also why it sheds moisture more easily.

Disclosure: If you shop from my article or make a purchase through one of my links, I may receive commissions on some of the products I recommend.

Common questions about perlite vs. vermiculite

Can you use perlite or vermiculite in organic gardening?

Perliteandvermiculiteare both natural mined minerals. Although they go through some physical processing, they’re both USDA-approved for use in certified organic agriculture. So if you do organic gardening, then yes, perlite and vermiculite are considered safe “organic” additives.

Can you grow plants in just vermiculite?

Because of its excellent water-holding capacity, vermiculite works well on its own as a growing medium for seedlings that need constant moisture without being oversaturated.

It’s especially good forindoor seed startingas vermiculite promotes faster germination and helps anchor young root systems, whether it’s used alone or as part of soil orsoilless mixes.

Can you mix perlite and vermiculite?

Yes, you can mix perlite and vermiculite in yourseed-starting mix or potting mix, since each ingredient has different functions and benefits.

Perlite acts as an aerator, helping the soil shed water. Vermiculite acts as a sponge to help the soil hold moisture. Both of them work in tandem to give your soil the right balance of drainage and water retention.

Can you use perlite or vermiculite in a raised bed?

You can use perlite or vermiculite directly in raised beds and in-ground garden beds to improve soil structure.

Mix the perlite or vermiculite into your existing soil so each ingredient makes up around 10% to 50% of the total volume of soil, depending on how much drainage or water retention you need.

What happens if you breathe in perlite and vermiculite dust?

The dust created by perlite and vermiculite are one of the biggest disadvantages of handling the materials. While they’re regulated as a “nuisance dust” by OSHA (Occupational Safety and Health Administration) and are not considered hazardous, long-term inhalation may make the lungs more susceptible to irritation or respiratory disease.

If you’re sensitive to dust or plan to handle large amounts of perlite or vermiculite in the garden, you can mitigate any problems by wearing a dust mask or covering your nose and mouth with a bandana.

This post updated from an article that originally appeared on February 27, 2020.