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 one of 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 in how much moisture each retains can make or break a gardening project.
Vermiculite and perlite are not the same thing, even though they may look the 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.
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.
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 never be 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 and drain), but these qualities are what make perlite so good at providing oxygen to plant roots and improving soil structure.
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.
Perlite and vermiculite are two common soil amendments that gardeners often use together in potting mixes and seed starting blends. Both are lightweight, mineral-based materials that help improve aeration and moisture retention in soil mixes. However, each has some unique properties that make them suited for different uses. Understanding the differences between perlite and vermiculite can help you determine when to use them alone or blended together.
What is Perlite?
Perlite begins as a volcanic rock that is crushed into small particles and then heated at extremely high temperatures. This causes the perlite to expand into lightweight, white particles that resemble styrofoam beads.
The key benefits of perlite include:
- Lightweight – weighs less than 10 lbs per cubic foot
- Improves aeration – creates air pockets in soil
- Promotes drainage – allows excess water to drain freely
- Neutral pH
- Holds some moisture and nutrients on its porous surface
Perlite is an excellent amendment for container mixes and seed starting blends because it prevents soil compaction while still retaining some moisture It’s especially useful for plants that require well-drained soil like cacti and succulents The porous structure helps oxygen get to plant roots,
What is Vermiculite?
Vermiculite is a mineral that comes from mica. It also undergoes heating to cause it to expand into lightweight flakes.
The main advantages of vermiculite are:
- Lightweight
- High water holding capacity – acts like a sponge
- Improves aeration
- Supplies some nutrients like magnesium and potassium
Vermiculite is prized for its water retention abilities. It can absorb water and nutrients and slowly release them to plant roots. This makes it well-suited for seed starting mixes and for moisture-loving plants.
Using Perlite and Vermiculite Together
Many gardeners find value in using both perlite and vermiculite together in their potting soil mixes. This allows you to get the benefits of both products in one blend.
Here are some of the key reasons to use perlite and vermiculite together:
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Balances moisture retention and drainage – Perlite provides drainage while vermiculite retains moisture. Using both creates a good balance of air and water in the soil.
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Versatility – A blend of perlite and vermiculite can be used for a wide variety of plants with different needs. You don’t have to customize mixes for each type of plant.
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Improves nutrient retention – Vermiculite holds onto dissolved nutrients and keeps them from washing out with excess water drainage. Perlite allows good drainage so salts don’t build up.
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Lightweight mix – Combining perlite and vermiculite creates a very lightweight potting mix that’s easier to handle.
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Lowers cost – Buying perlite and vermiculite in bulk and blending them is often cheaper than buying pre-mixed potting soils.
Mix Ratios
There is no single perfect ratio for mixing perlite and vermiculite. You can tailor blends to suit your specific needs. Some common blended ratios include:
- 1:1 perlite to vermiculite – balanced blend suitable for many plants
- 2:1 perlite to vermiculite – improved drainage for cacti and succulents
- 1:2 perlite to vermiculite – increased moisture retention for seed starting
A good starting point is an equal 1:1 ratio. From there you can adjust to add more perlite for drainage or more vermiculite for water retention as needed.
When mixing your own blends, start with a basic soilless potting mix as your base. Then add perlite and vermiculite to improve the blend.
For seed starting, a mix of 1 part potting mix, 1 part perlite, and 2 parts vermiculite provides an ideal lightweight and moisture-retentive medium for germinating seeds.
Using Perlite vs Vermiculite
While perlite and vermiculite work well together in blends, there are times when one may be better than the other for specific uses:
Use perlite for:
- Cacti, succulents, and plants that need fast drainage
- Maintaining humidity for orchids and bromeliads
- Rooting cuttings
- Improving drainage in existing potting soil
Use vermiculite for:
- Seed starting mixes
- Moisture-loving plants like African violets
- Water retention in indoor potted plant soil mixes
- Hydroponic growing mediums
Common questions about perlite vs. vermiculite
Perlite and vermiculite are 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.
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 less porous 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.
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- You want to loosen heavy clay soil. Perlite helps break up surface crusts and reduce soil compaction.
- You’re repotting houseplants or plants that like to stay on the drier side. Shade-loving houseplants, succulents, and cacti do better with less water, so a potting mix amended with perlite helps prevent root rot and fungal disease.
- You garden in a wet or humid climate. Adding more perlite to containers or garden beds helps keep the soil from becoming waterlogged.
- You’re starting seeds. Because vermiculite holds moisture better than perlite, it helps keep seeds from drying out during germination. Vermiculite is an excellent choice for covering hard-to-start seeds or seeds that need light for germination.
- You’re repotting outdoor container plants. Potted plants tend to dry out faster outside, especially if they’re in porous containers like terra cotta or fabric pots. Adding vermiculite to your potting mix helps them retain moisture better.
- You garden in a dry climate. Adding more vermiculite to potting soil and soilless mixes conserves moisture in the growing media.
Perlite vs Vermiculite
FAQ
What is the ratio of perlite to vermiculite in potting mix?
- 1 part vermiculite, or perlite
- 1 part peat moss, or coconut coir
- 1 part high-quality finished compost, or worm castings
Can I add perlite and vermiculite together?
Yes, you can combine vermiculite with other materials, like perlite, to create a balanced growing medium that improves drainage while simultaneously retaining water.
What plants do not like vermiculite?
Plants such as cacti and succulent varieties do not like vermiculite because it’s very good at retaining water, and they prefer soils that are well-draining. If using vermiculite with these plant types, you run the risk of root rot.
When not to use perlite?
When Should You Stay Away from Perlite? Since perlite is non-toxic, it’s generally safe to use in both an indoor and an outdoor setting — especially if you have curious cats and snooping dogs. However, using perlite in excess creates large dust clouds, so it might not be the best choice for those with asthma.
Should you use perlite or vermiculite in your garden?
When it comes to choosing between perlite and vermiculite for your garden, each has its own unique benefits. Perlite is great for improving aeration and drainage, while vermiculite is excellent for retaining moisture and nutrients. Here’s what I’ve learned over the years about both.
Can you mix perlite and vermiculite?
Yes, you can mix perlite and vermiculite in your seed-starting mix or potting mix. Each ingredient has different functions and benefits. Perlite acts as an aerator, helping the soil shed water, while vermiculite acts as a sponge to help the soil hold moisture.
Are perlite vs vermiculite safe?
Yes, both are natural, non-toxic, and approved for organic gardening. Conclusion: Which One is Best for Your Garden? Choosing between perlite vs vermiculite depends on your soil, climate, and plant needs: Use perlite for aeration and drainage. Use vermiculite for moisture retention. Mix them for the best of both worlds.
How much perlite & vermiculite should I put in my soil?
As a general rule, do not exceed 50% perlite or vermiculite in your soil, potting mix, or growing medium. The rest can be compost, peat (substitute) or just soil, etc. However, keep in mind that these are soil improvers, they are not soil!
Are perlite vs vermiculite a good soil amendment?
Gardening success starts with the right soil amendments, and two of the most commonly debated options are perlite vs vermiculite. These lightweight minerals are widely used to improve soil aeration, moisture retention, and plant growth, but they serve different functions.
How do you use vermiculite?
Mulching: Apply a thin layer around plants to help retain soil moisture in dry conditions. Soil Amendment: Work vermiculite into sandy or fast-draining soil to increase moisture retention. Hydroponic Growing: Use vermiculite as a standalone medium or mix with perlite for improved water retention.