Thursday, December 9, 2010

Perlite vs. Vermiculite: How to tell the Difference

Several years ago, I had an experience where I specifically needed perlite for a gardening project. When I got to the gardening section of this store, I discovered that they were out of perlite. I asked a store employee for help, and he confirmed that perlite was indeed out of stock everywhere in the store. Instead, the employee tried to sell me vermiculite, insisting they were basically the same thing. While this is true in one respect, this mistake could also ruin your project. While working for the same purpose in one respect, perlite and vermiculite are completely opposite in another. So it is important to know the difference between perlite and vermiculite so that you are never influenced to do something that could ruin your gardening projects by incompetent store employees.

Vermiculite and perlite are both non-organic soil additives that are used to aerate the soil. As rooting mediums, they offer this same benefit. Vermiculite is a spongy material made from mica whereas perlite is a type of highly porous volcanic glass that resembles pumice. Perlite appears as small, round, non-uniform, white particles. Some people mistake perlite in potting soil mixtures for Styrofoam balls. While both mediums are used for aeration, they cannot always be used interchangeably.

Both perlite and vermiculite are great at retaining water, but vermiculite retains much more water and offers a little less aeration than perlite. Vermiculite literally acts as a sponge that will retain water to the point of saturation. Perlite holds water by having a large amount of surface area within the nooks and crevices of its vast pores. But being porous and made of volcanic glass it allows excess water to drain much more readily than vermiculite.

In a case where you have especially thirsty plants and want the soil to hold extra water, vermiculite would be a better choice. You might find that perlite will dry out too quickly in this situation. But if you were growing cacti, you would eventually discover that the amount of water vermiculite holds would lead your plants to rot. Perlite, on the other hand, would be well-draining and suitable for your cacti mixture.

Vermiculite is also used in mycology to add moisture to the substrate that mushrooms will grow on. Perlite would fail miserably at this task. Perlite can also be used in mycology or horticulture to raise humidity levels. Because perlite has more surface area, it fosters higher humidity by evaporation off this extra surface area. Vermiculite would not work as well for this though because it would retain much more of that water.

So essentially, perlite and vermiculite are the same in that they can retain more water than many other things, and they can aerate soil. But vermiculite differs from perlite because it retains water and creates a soil mixture that retains water, whereas perlite fosters a well-draining soil mixture. Likewise, vermiculite’s tendency to retain water makes it a good additive to mushroom substrates but a bad candidate for increasing humidity. Perlite’s hard, porous nature makes it a great mechanism for increasing the humidity of a given area but disqualifies it as a candidate for creating a substrate that will retain moisture.



  1. This is an extremely helpful post, just what I was looking for. Thanks for taking the time to share. Mark (of Vertical Veg)

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  3. Thank you for this information. I am new to succulentsee and you just saved my plants!!!!!

  4. Really like this information, thank you for your kindness. I'm going to buy these soil additives, but I don't know what to choose between these twos.