What Vermiculite Does for Potting Mix and Plants
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Vermiculite is a magnesium silicate that is a byproduct of two types of minerals (biotite or phlogopite) that go through a process of weathering or hydrothermal alterations (they’re heated up) that leaves it in a porous and accordion like formation that allows it to aerate while retaining moisture making it perfect for use in potting mixes .
Although it does retain moisture, vermiculite also allows for the free flow of excess liquids by not letting soil or potting mix compact and become a dense layer. When liquids can drain through the potting mix and materials, it helps prevent waterlogging and diseases like root rot which keeps plants growing healthy.
Fun fact: The name vermiculite originates from the Latin word “vermiculor” which means little worm or wormlike body and was given because of its ability to grow and have a worm-like shape. Just like worms in the soil which help aerate dirt and improve drainage, vermiculite does the same in potted plants. The name was given long before it was used in potting mixes.
Curious about how vermiculite gets its shape, alternative materials you can use in potting mixes and why, or want to know some fun facts? This guide to vermiculite and potting mixes has these answers and more.
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How Vermiculite Gets its Shape, Color, and Texture
Vermiculite starts as a magnesium silicate as either biotite or phologopite and is currently mined in South Africa, China, and Brazil. Biotite is a darker color in shades of brown, green, or black, while phologopite can also be green like biotite, or yellow and reddish-brown. When these minerals are heated to 1,800 Fahrenheit or 1,000 Centigrade, they begin to expand via a process called exfoliation .
As the mineral expands the water heats up inside and begins to release as steam, this is what gives vermiculite its rough and accordion like appearance and texture. Raw and natural vermiculite has gold, silvery, and grey tones and lacks the shape and color you see in potting mixes. The signature shape and color we see for plants is from the exfoliation process. This shape is why it is one of the most popular materials used for potted plants.
Why it is Used in Potting Mixes
Vermiculite is a popular ingredient in potting mixes because of its ability to retail moisture, improve drainage, and aerate potting mix. Its spongy and porous structure helps it to retain moisture with a gradual release which helps ensure plants can stay hydrated.
Because it is porous, it can also create air pockets after the moisture has left to help prevent potting mixes from compacting, giving a plant's roots room to breathe, expand, and helps with drainage. Vermiculites ability to retain moisture and increase drainage makes it one of the best materials for potted plants.
Fun fact - Vermiculite’s first appearance as a mineral studied for use was in 1824 by Thomas H. Webb in Massachusetts, but it wasn’t until the early 1900’s that it began being used for commercial purposes where it was mined in states like Colorado and Montana. The Montana mines remained operational until the 1990s which supplied 70% of the United States Vermiculite consumption. It’s been found towards the eastern and central US in areas rich in Biotite like Arkansas during coal mining in the 1940s and 1950s.
Vermiculite vs. Perlite
You’ll see both vermiculite and perlite in potting mixes, and although they are interchangeable as they serve the same purpose, vermiculite tends to be more expensive than perlite because it is more scarce and expensive to manufacture. Perlite is also not naturally occurring as it comes from a process where obsidian is heated up so that water can escape giving it a new form and color, while vermiculite can be found naturally occurring.
Although vermiculite costs more than perlite, it is better at retaining moisture than perlite because of its ability to act like a sponge, so plants that need more moisture retention like Prayer Plants (Calathea) and Hoya will do well with it. Perlite is better than vermiculite for drainage so houseplants like Snake Plants (Sansevieria) and Cacti will do better with it.
Vermiculite is a naturally occurring mineral that works great for potted plants due to its ability to retain moisture, help with drainage, and provide aeration in the potting mix. Now you know where it comes from, how vermiculite gets its signature shape, and have some plant fun facts to share with your friends and family.
