Potting soil can be confusing for gardeners. Different plants have different needs, and choosing the right potting soil can sometimes mean the difference between failure and success for your plants. However, there are many different types of potting soil to purchase, each offering their own formulation with different benefits. I thought I would compare the most common potting soil additives: perlite and vermiculite.

What Is Perlite And Vermiculite? Perlite and vermiculite are both non-organic additives that help aerate soil.  Their main use is to allow gaps in the soil, air pockets, so that water can drain out of the soil easily and allow air to circulate among the roots. This is great for preventing your potting soil from becoming a swampy mess every time you water your plants.

On top of aerating the soil, both perlite and vermiculite also can hold some water and release it slowly into the soil. Using soils that contain one or both of these additives means you need to water your plants less frequently.

Perlite and vermiculite are both sterile additives that will not introduce potential diseases or fungi into your potting soil. And they are both pH neutral so they do not affect the pH of your soil, something that some plants are very picky about. Both are non-toxic, safe to use with any plants, and very inexpensive.  Because of this, these are the most common additives that you see in various potting soils. Perlite and vermiculite are both used in a similar manner, but they are not interchangeable. They are quite different in composition and in how they improve your potting soil.

Perlite:

Perlite is volcanic glass that has been heated to extreme temperatures. The glass particles expand to about 10 times their size and are full of tiny air compartments. The enlarged particles often resemble tiny pieces of styrofoam, and in fact, many new gardeners sometimes mistake them for either styrofoam or assume they are fertilizer pellets. Perlite is extremely porous, allowing water to drain from the soil easily. Because each piece is made from tiny crystals, it also has a large surface area which allows trapped water to evaporate off it extremely well and also hold air. Perlite is great for use with plants that need well draining soil. It is frequently found in cactus potting soil, but works great with any plant that loves dryer soils or a plant that prefers to dry out completely between watering.

Vermiculite:

Vermiculite is the name for a group of minerals (aluminum-iron-magnesium silicate) that have many uses, especially in construction and horticulture. These minerals are mined from surface mines and broken into dry flakes, which are then heated until they expand. The dry flakes can grow into worm-like shapes when exposed to water. While vermiculite does aerate the soil a little, it lags far behind perlite in this skill. What it does best is retains water for the soil. Each thin, layered piece can hold up to 3-4 times its volume in water, releasing it slowing to the soil as it dries. This makes vermiculite perfect for water-loving plants, or any plant that hates having dry roots. Mushrooms are often grown in soil featuring vermiculite because of its ability to keep things moist. If your plants like a wetter soil, vermiculite is the best choice.

Which To Use? Both perlite and vermiculite are great potting soil additives. Deciding which one to use really depends on what plants you are growing and their needs. Before you purchase potting soil, check the soil requirements for each plant. Many gardeners find they have to use two potting soil types so they can have one of each additive on hand for their plants.

Resource: University of Minnesota Extension