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Gardening with Perlite and Vermiculite

Perlite and Vermiculite: Mix Ratio & Soil Enhancements

Perlite & Vermiculite

If you garden regularly or just putter around with plants and flowers, you’re probably familiar with vermiculite and perlite. Most plant-friendly people are. Even people who don’t garden know the pair have something to do with dirt and plants, although few could tell us their specific role. Many people wanted to know the following:

What are perlite and vermiculite? How are they used? How are they made? Are they the same thing? Do they serve the same purpose? Are they natural, chemical, or man-made? You’ll learn the answer to these questions and even a few perlites of wisdom in this informative gardening soil article.


Perlite is a natural silicate rock, meaning it contains a large amount of silica (SI) in its composition, according to the Mineral Information Institute. Perlite is also a mineral that retains a fairly high water content between 2 and 5 percent. That moisture plays a critical role in transforming mineral from rock into the lightweight perlite found in garden centers and nurseries.

Perlite begins its life as obsidian or volcanic glass. The rapid cooling of lava before crystallization creates obsidian. Water has to come in contact with and hydrate obsidian to form perlite. It is this naturally occurring process of moisturizing that gives perlite its unique properties when processed.

The Process

The final bagged product of perlite we pick up at our favorite garden store is a far cry from its original structure when first mined. Earthmoving behemoths exhume perlite from open-pit mines where it eventually finds its way into a rock crusher. Afterward, companies sort perlite according to grade.

After extraction, the company transfers this volcanic glass to a facility where large furnaces await. They load the perlite into the furnace and heat it to a temperature of 1,600 degrees Fahrenheit or 871 degrees Celsius. At this temperature, transubstantiation occurs within the rock.

The moisture content within the glass vaporizes causing it to burst suddenly like a kernel of popcorn. This mini-explosion greatly expands the perlite, causing it to swell up to 15 times its normal size and become a soft, spongy material. This finished product becomes the final soil amendment in home gardens due to its water retention capabilities and ability to aerate the soil.

Moreover, perlite is extremely lightweight, weighing only 5 to 8 pounds per cubic foot. That’s pretty astonishing considering, by contrast, a cubic foot of dry, loose potting soil weighs between 75 and 110 pounds. Additionally, the newly formed perlite contains tiny compartments of air with its exterior possessing moisture-absorbing cells. Its whitish look and spongy feel often lead it to be mistaken for Styrofoam balls in a plant’s pot.

While incredible in many ways for the gardener, there are multiple uses for perlite in construction, as well as industrial implementations. Perlite is a common material in roofing insulation, masonry as a block filler to reduce noise levels, and numerous other applications. For this article, we will primarily concern ourselves with the horticultural applications of perlite.

As a Soil Supplement

In the garden, adding a ratio of perlite to soil or using it as a standalone soilless medium is commonplace. Perlite particles, when mixed into dirt or moss, create little clefts and air pockets that allow water and oxygen to proceed unimpeded to the plant’s roots. This unique characteristic encourages the dispensation of nutrients to the roots and, by creating space within the dirt, promotes better drainage of the soil. For roots, perlite is a favorable medium.

These properties are particularly important because a plant absorbs over 95% of its oxygen through its roots. Poor soil drainage can keep a plant’s roots wet, leading to root rot, as well as inhibit oxygen absorption, causing the roots to suffocate and leading to plant death. Combining soil, perlite, and proper watering creates a suitable plant environment.

Additionally, due to the unique shape of each perlite particle and its permanency, moisture and nutrients hold fast to the tiny crevices on the surface until the plant requires them. The granular quality of perlite allows for extensive drainage of any excess moisture that may accumulate. This channeling is paramount to growing a healthy plant that doesn’t like wet soil. Estimates project that overwatering causes nearly one-half of all plant fatalities.

Helping Houseplants Receive More Light

This extraordinary little supplement also possesses an important light-reflecting capability that can be beneficial to houseplants during periods of lower light, such as overcast days or during the short-sunned winter months. Winter can be a dry time for house plants because home heating significantly dries out the air inside, causing the tips of the plants to become brown and brittle.

By placing a tray of water near your plants with some perlite in it or by adding perlite on the surface of the potting mix containing the plant, you can significantly increase the value of the sunlight it receives through the window as the perlite acts as a reflector that directs light back to the plants. This reflection can make a massive difference in the overall health of the plant and promote good plant vigor.

TIP: By keeping the perlite moist, you can increase the humidity surrounding your plants, allowing them to take advantage of the extra moisture. While on the subject, vermiculite retains much more water due to its larger surface area, which creates even more humidity than perlite as it evaporates. More on vermiculite later.

Mix & Match

As mentioned, perlite makes an excellent amendment to straight soil in the right ratio, but it can also be an exclusive grow medium. It works well when mixed with equal parts of sphagnum moss, coco coir, or peat moss, but it depends on the perlite mix ratio. For the best results, you should shred the moss or coco coir before introducing it to the mix.

This combination of perlite and moss makes an all-natural grow medium that covers all the bases of good soil requirements. This ratio retains moisture while at the same time allowing for good drainage and oxygenation, which are crucial for a healthy plant. It aerates the soil due to each particle of perlite having its own irregular shape. Additionally, nutrients and moisture cling to the cracks and fissures on the surface, where plants can get them as needed.

Plants started from seed will appreciate the easier path provided by perlite, as its lightweight structure and lack of density permit their tiny shoots to push through to the surface with less resistance. The roots enjoy this perk as well. Other mediums would offer too much resistance for these roots and shoots to push through.

Water and Perlite

When it comes to watering indoor plants, they can be a bit finicky. Plants in general like a lightly but continuously moistened soil. Some plants, such as succulents, don’t require watering as often because they retain moisture in their broad, glossy leaves. Succulents prefer to go a bit dry before refueling. It can be tricky knowing when to water these plants and when to let them dry out. This situation is where incorporating perlite into the potting soil can help.

If an indoor plant, such as Jade or another succulent, dries out too much, which happens because people feel they don’t need to water them, this occurrence can cause the dirt to shrink up to where it separates from its container. When this shrinkage occurs, any water you add will run off the sides, and the remaining soil containing the root ball will not absorb it. Hard, dry dirt doesn’t absorb water readily, which is why flash floods occur. That principle remains the same even with a potted plant.

If you do encounter this problem, take the pot containing the plant and let it soak in a pan of water until it rehydrates completely. Add some soil mixed with perlite afterward to fill in the gaps. Fill it up to near the top of the pot and add water lightly.

Perlite works to help the plant receive and maintain the correct amount of water and nutrients. Its scrobiculate surface retains excess moisture, which the plant can extract when it begins to dry out. These characteristics make perlite useful to both the plants and the gardener.

This unique ability is especially beneficial for those of us who aren’t quite sure when to water succulents and for those who occasionally forget.

Perlite & Root Cutting

Perlite makes an excellent starter medium for cuttings, also known as clones. By itself or mixed, cuttings and roots seem to thrive in perlite, but there are two things you can do to help expedite the growing process. Keep the perlite moist and protect the cuttings from direct sunlight. Warmer temps will produce roots and new plants faster than when grown in colder temperatures. Too much direct sunlight can toast new shoots.

Got it-Now What About That Vermiculite?

Vermiculite is non-organic soil and is similar in certain ways to perlite, but there are some distinct differences. Both are lightweight, water retentive, non-toxic, and fireproof, making them alike in that sense, but industries utilize them differently. One major difference lies in the fact that perlite originates from volcanic glass, whereas vermiculite contains mica, a sheet silicate mineral. Companies heavily mine both substances. Vermiculite mines exist in South Africa, China, Russia, and Brazil. Like perlite, vermiculite also has many industrial applications.

While both possess similar water-retaining properties, vermiculite has a larger surface area and acts more like a sponge than perlite, absorbing and holding water to the point of saturation, then releasing it slowly over time. It also creates a soil environment that retains water. If you are growing a cactus or other plants that have low water needs, vermiculite is not the correct amendment for those types of plants. You will need a medium that offers quicker draining, such as sandy soil, coco coir, or a mix of different materials. Your best bet is to get some perlite in this instance.

Switch plant types, however, and things change. If you were growing mushrooms, for example, vermiculite would be an excellent choice for an additive to the substrate, the surface from which they grow, because of its moisture retentive properties. Vermiculite is also effective at aerating or expanding the soil.

That’s a Wrap

So, there you have it. All you need to know about perlite and vermiculite and how to choose the one best suited for your plant’s particular needs. Knowledge is power, and power feels good.

Now the next time you hear someone discussing perlite or vermiculite, you’ll not only know what they’re talking about, but you’ll also know what you’re talking about too.

Happy planting!

Alan Ray