by Matt Gibson and Erin Marissa Russell
If you are standing in the gardening center, trying to figure out which additive your soil needs the most, wondering what the difference is between perlite and vermiculite, then this article is for you. The two additives are similar, but they are distinctly different in a few important ways. Read on to learn more about these two all-natural soil amendments that gardeners use to change the water retention and nutrient retention levels in their garden soil.
What Is Perlite?
Perlite is made from volcanic rock, which is heated and crushed until it explodes in order to transform the rock into small white pieces. It has medium water retention ratings and low nutrient retention ratings. It is added to soil mixes in order to improve the drainage capability of both soil-based and soilless potting mixes.
Perlite helps insulate plant’s roots from extreme temperature fluxuations. It’s also used as a protective coating on pelleted seeds. Perlite is lightweight, odorless, clean, and easy to handle. It has a pH of 6.6 to 7.5. Add perlite to your soil for plants which need their soil to dry out between waterings, such as cacti or succulents.
- Perlite is great for seed starting mixes and blending your own custom potting soil mix
- Helps lighten and loosen heavy, compacted soils
- White granular pieces that contain about 6 percent water
- Perlite has a neutral pH level
- Holds nutrients and three to four times its weight in water
- Clean, sterile, odorless, and non-toxic
- Works as a lightweight sand substitute
- Won’t rot or mold
- Tends to float to the top of potted plant containers due to its light weight
What Is Vermiculite?
Vermiculite is magnesium-aluminum-iron silicate. It is an all-natural mineral product that is mined out of the ground and then processed into a soil additive that mainly increases water retention and nutrient retention levels in soil. It looks similar to mica with its layers or stacks, which are suited for trapping water. It has high water retention and high nutrient retention levels. Vermiculite’s water-holding capability makes it perfect as an anti-caking agent in dry pesticides and fertilizers.
Contrary to rumor, vermiculite does not contain asbestos and it is not a type of asbestos. This rumor is due to some vermiculite that happened to be contaminated with asbestos in a mine in Libby, Montana, which was closed in 1990 due to the contamination. Vermiculite from other sources has since been tested and proven to be asbestos free and harmless. The medium is considered safe for commercial and personal use.
Vermiculite is best used for water-loving plants that need their soil to stay moist at all times. Add a healthy scoop of vermiculite to the potting soil of plants that like lots of water.
- Great for seed starting or blending your own custom potting soil mix
- Helps to lighten and loosen heavy, compacted soil types
- Helps soil retain moisture and gives plants nutrients
- Mixes easily and well with soil
- Clean, sterile, non-toxic, and odorless
Vermiculite and Square Foot Gardening
Mel Bartholomew, author of Square Foot Gardening, describes vermiculite this way, “As you probably know it holds water yet drains when it’s filled, just like a sponge does. The plant roots grow around the particles and take in whatever moisture they need and since the particles of vermiculite take a long time to dry out, moisture is always there for the plant, enabling it to grow quicker and more healthy.” It is one of the three combined ingredients in his recommended soil recipe for the popular Square Foot Gardening method. The complete soil recipe consists of one third vermiculite, one third compost, and one third peat moss.
Mel has always been a big fan of vermiculite and thinks that it is far superior to perlite. He calls vermiculite, “the most marvelous natural material,” and says that even though perlite is much cheaper, he doesn’t mind paying up for vermiculite, particularly the coarser size of the material.
Common Traits of Perlite and Vermiculite
Perlite and vermiculite are both lightweight sand substitutes for soilless potting mixes which are often used to improve aeration and texture in potting soil and garden soil mixtures. Both are odorless, sterile, disease-free, insect-free, and seed-free. Neither medium will rot, deteriorate, or decompose.
Both mediums are used as an ingredient in soilless potting mixes that are made for the cultivation of plants as well as for seed germination, propagation, hydroponics, containers, and transplants. They are both also commonly used as carriers in dry fertilizers, pesticides, and herbicides to improve coverage.
Differences Between Perlite and Vermiculite
Both perlite and vermiculite are put to use in the garden to improve drainage, prevent compacted soil and increase moisture retention. They are both used in propagation of new plants and for seed starting and cultivation for indoor growing, outdoor growing, and composting. The differences in the way each medium retains water and how much water each medium can retain make them suitable for different applications.
Vermiculite is perfect for plants that enjoy lots of water, such as some irises and forget-me-nots. Perlite dries out too quickly for water-loving plants. The amount of water that vermiculite holds is too much for plants like cacti, succulents, or rhododendrons, which need a well-draining soil. Using vermiculite for plants like these could lead to root rot or death.
Common Questions and Answers About Perlite and Vermiculite
Are vermiculite and perlite the same?
Although it’s a common misconception, vermiculite and perlite are not the same. Vermiculite is a silicate material that’s brown or beige in color and has a soft, sponge-like texture. Perlite is harder, is white in color, and is made out of mined volcanic rock.
Vermiculite and perlite also differ when it comes to pH level, which may be a consideration when you’re choosing which to add to your soil. Perlite is slightly alkaline, while vermiculite tends to be closer to neutral. (If you aren’t sure what your soil’s pH level is, our article “How to Test pH in Your Soil” can help.)
Vermiculite and perlite do share many qualities. Both products are inorganic, lightweight, and relatively sterile. And of course, both are used as a soil amendment to aerate soil—though perlite provides more aeration than vermiculite. Both perlite and vermiculite are highly porous, making them able to hold water in the soil so it’s available for your plants. However, vermiculite holds more moisture and keeps it available in the soil longer than perlite will.
So how do you know which one you should choose? If the plants you’re growing need the soil to stay on the wetter side, opt for vermiculite. Vermiculite is also the best choice if the plants in your garden are sensitive to alkalinity in the soil. Vermiculite is also the go-to when it comes to starting seeds because it protects seedlings against damping-off and other fungal diseases that can threaten them as they start to grow.
Although perlite doesn’t hold onto water as long as vermiculite, it boosts the humidity as it releases the water. Many plants thrive in high humidity, so if that’s a concern in your garden, perlite is right for you. Perlite is optimal when it comes to rooting cuttings from established plants because it helps prevent the rot that can otherwise be a challenge. Perlite is also the best option for planting epiphytes, cacti, succulents, and other plants that require plenty of drainage and aeration (and can tolerate a slightly higher pH level).
In short, choose perlite for cacti, succulents, epiphytes, when you’re rooting cuttings, and whenever quick drainage or maintaining high humidity is a concern. Opt for vermiculite to start seeds or whenever you’re working with plants that need their soil to retain moisture.
Can I mix perlite and vermiculite?
There’s really no need to mix perlite and vermiculite because each of them is best suited for different situations. Use perlite to root cuttings or grow cacti, succulents, epiphytes, and other plants that benefit from quickly draining soil with plenty of aeration. Perlite can also offer a humidity boost to plants that need it. Vermiculite is better suited for starting seeds and other situations when plants require plenty of moisture consistently available in their soil.
Can perlite be reused?
Yes, perlite can be used again after it’s been used to grow plants. That’s because perlite doesn’t decompose and doesn’t hold onto nutrients. To reuse your perlite, simply pick through it to remove any plant bits you find, such as root segments. Then rinse the perlite thoroughly. If sterility is a concern, you can sterilize your perlite in 10 percent bleach solution. (Use water to dilute.) After soaking in the bleach mixture for 20 minutes, rinse thoroughly.
Can you grow plants in just perlite?
Most plants can be grown with success in perlite without anything else added to it. You will need to water your plants, of course, and supply them with nutrients from an appropriate fertilizer.
Can you mix perlite with soil?
Mixing perlite into the soil in your outdoor garden beds or combining it with potting soil or another medium is the most common way to use perlite. To start seeds, use a mix of half perlite and half peat. Cuttings can use this mix too, or you can up the perlite to 100 percent. For garden beds, spread a two-inch layer of perlite, then mix it into the top six to 12 inches of soil. Potted plants can use a third perlite and an appropriate potting soil for the rest.
Does perlite decompose?
Perlite does not decompose over time because it is made from superheated volcanic rock. When you add perlite to soil, you’re permanently changing its texture and making it better for growing plants.
Does vermiculite decompose?
Vermiculite does not break down or decompose when it’s used in potting soil. That means vermiculite is a permanent way to amend and improve your soil.
Does vermiculite help drainage?
Vermiculite helps hold moisture in the soil so it’s consistently available for plants to use. If you’re looking for a soil additive to help make sure plants get plenty of drainage and aeration, perlite is a better option.
How much perlite do I add to soil?
How much perlite to add depends on what you want to grow. For seed starting, use half perlite and half peat. Cuttings can be rooted in this same mixture, or you can increase the perlite up to 100 percent. For potted plants, use one third perlite and two thirds potting soil. Garden beds get a two-inch layer of perlite mixed into the top six to 12 inches of your garden soil.
Is perlite a Styrofoam?
Although perlite does resemble Styrofoam, it is not Styrofoam. Perlite is a naturally occurring volcanic rock that has been heated and crushed until it changes in color and texture.
Is perlite good for clay soil?
Perlite is an excellent amendment for clay soil when you want to increase the drainage and aeration of the soil. Till or loosen your clay soil to a depth of six to 12 inches, then spread a four-inch layer of perlite across the top. Mix the perlite into the soil you already loosened. If your clay soil could use a boost of organic material, use half perlite and half peat for this process.
Is perlite good for succulents?
The drainage and air circulation perlite offers makes it an excellent soil amendment for growing succulents. Use one part potting soil (choosing one without vermiculite that offers excellent drainage), one part coarse sand, and one part perlite.
Is perlite safe for organic gardening?
Perlite can be processed organically. It’s a naturally occurring mineral that’s superheated and crushed. Look for packaging that is labeled “organic.”
Is vermiculite organic?
Vermiculite can be organic, but it is not always organic. Vermiculite is a naturally occurring mineral that humans mine, heat up, and package for gardeners to use. When the mining and processing is done organically, vermiculite is organic. Look for packaging marked “organic.”
Is vermiculite safe for gardening?
As a naturally occurring mineral, vermiculite is very safe to use. Rumors to the contrary that you may have heard are linked to one mine, which is now closed, which produced vermiculite tainted with asbestos fibers. Vermiculite currently on the market does not contain asbestos.
Should I add vermiculite to my soil?
Add vermiculite to soil when you’re making a seed starting mixture or whenever your plants need water to stay locked into soil so it’s consistently moist. Vermiculite is also a great choice when you’re working with plants that are susceptible to damping off or other fungal diseases.
What does vermiculite do in potting soil?
Vermiculite increases soil’s ability to retain water, letting it hold on to more moisture and stay damp longer. Vermiculite in potting soil also helps the soil retain nutrients and keep them available for plants.
What is perlite good for?
Perlite specializes in aerating soil and helping it to drain quickly. That makes perlite beneficial for plants that are susceptible to rot diseases. Adding perlite to your soil also increases humidity, which some plants need to thrive. Perlite is also an excellent option for rooting cuttings or growing cacti, succulents, and epiphytes.
What is perlite made from?
Perlite is made from volcanic glass (obsidian) with water trapped inside that is then superheated by humans and crushed until it changes in color and texture. The water trapped in the volcanic glass has a popcorn-like reaction when superheated and crushed, turning the substance white and making it foam-like.
What is the purpose of perlite in potting soil?
Perlite is used in potting soil frequently because it’s a great amendment for increasing the drainage of soil, loosening it up, and letting air circulate through the soil more freely.
What is vermiculite used for in gardening?
Vermiculite aerates soil and increases its ability to retain moisture (holding more water for longer) and retain nutrients, making them more consistently available to your plants.
What is vermiculite used for in plants?
Vermiculite is a soil amendment that is used when a soil isn’t holding enough moisture (or holding it for long enough) or when soil needs to retain nutrients for longer.
Want to learn more about using perlite versus vermiculite?
Better Vegetable Gardening covers Using Perlite in Potting Soil
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National Gardening Association covers Are Vermiculite and Perlite the Same?
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Gardening Know How covers Vermiculite Growing Medium
Get Busy Gardening covers DIY Succulent Potting Soil
Green and Vibrant covers Perlite
Maximum Yield covers Perlite for Hydroponic Gardens
NY Times covers Soil Mixture Recipes
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Vermiculite.org covers What is Vermiculite
Washington Post covers More on Potting Mix