What Is Vermiculite? Here's How to Use This Mineral, Which Can Replace the Soil in Your Container Plants

Whether you are new to container gardening or have been growing greenery this way for years, you know that nutrient-rich soil is the foundation of a thriving plant. If you're hoping to improve your dirt, consider vermiculite, a naturally occurring mineral. Vermiculite can amend your soil for the better or it can be used in a homemade soilless potting mix. Either way, the mineral boosts the health of your container plants and creates a well-draining, nutrient-rich growing medium—whereas standard garden soil can be too dense for container gardens.

To understand how to best use vermiculite, we turned to a few growing professionals. Discover our expert-approved tips on how to effectively grow plants in vermiculite-based soil—plus, learn more about its other applications and when to use it in place of perlite, a more common gardening mineral.

What Is Vermiculite?

Vermiculite is a micaceous, naturally occurring mineral that looks like small brown flakes; it is commonly used as an ingredient in soilless growing mixes, says Niki Jabbour of SavvyGardening.com and the author of Growing Under Cover. "Once mined, vermiculite is heated so that it expands into a lightweight material," says Jabbour. "These gold flakes hold and release water, as well as nutrients, which is why vermiculite is prized as a component of potting mixes."

Why Vermiculite Is Used in Soilless Potting Mixes

Home gardeners, this mineral should be on your radar if you want to create your own potting mix. It's especially effective in soil for container gardens or houseplants, says Jabbour. "Vermiculite holds moisture and nutrients, improves the structure of soil, and adds loft to lightweight growing mixes," she says.

It also keeps your soil light and fluffy, says Jeana Myers, a North Carolina State horticulture extension agent. Pure garden soil is too dense for houseplants and doesn't support ample airflow like a vermiculite-based soil can.

How to Use Vermiculite as a Soilless Potting Mix

Commercial potting mixes typically contain vermiculite in the blend, but you can grow plants in a mix that stars this mineral. "I would typically blend 2 gallons of peat moss or coir with 1 gallon vermiculite, 1 gallon of perlite, and 1 gallon of compost," says Jabbour. "I'll also include a cup of a complete granular fertilizer."

Jabbour likes this recipe for a few reasons: "It results in a well-draining, nutrient-rich growing medium that, thanks to the vermiculite and perlite, is light and airy and holds water well," she says. "This mix is perfect for flower and vegetable containers, as well as starting seeds." If you are using peat moss instead of coir, add 1/4 cup of powdered lime, she says. The acidity from the peat moss and lime boosts the pH, which results in added plant growth.

Other Uses for Vermiculite

In addition to using vermiculite as a soilless potting mix, this mineral can be used for other gardening needs.

Bulb Storage

Vermiculite can be used to store flower bulbs over the winter. "Tender bulbs like gladioli, dahlias, and cannas won't overwinter outdoors in my zone 5 garden," says Jabbour. "Therefore, I need to lift them in autumn and store them for the winter."

To care for these plants, she waits until they naturally die back before carefully digging the bulbs or tubers from the soil; she then stores them in a cool, dark, and humid environment. It's important to store the bulbs or tubers in stable conditions (between 40 and 50 degrees), as temperature extremes can cause rot or damage. "I use ventilated cardboard boxes or large nursery pots to winter over bulbs and tubers," says Jabbour. "I add several inches of vermiculite and carefully nestle the bulbs or tubers into the material."

From there, she covers the bulbs or tubers with more vermiculite and tops the container with a loose plastic cover to ensure ample airflow. It's important to check on the bulbs and tubers every month to assess the moisture levels in the container. For tubers that appear shriveled, Jabbour recommends spritzing them with water. And if the vermiculite is moist, she suggests leaving the plastic covers off the boxes so the mineral can dry out.

Root Cuttings

Gardeners can also put root cuttings from houseplants, annuals, and perennials in vermiculite, where they will establish new roots. "For annuals like geraniums or coleus, I take a 3- to 4-inch-long stem cutting, cutting just below a node (the spot on the stem where leaves emerge)," says Jabbour. "I remove the lower leaves and slip the cutting into a 4-inch diameter pot filled with moist vermiculite."

This can be topped with a clear plastic bag to hold humidity. Place it in a bright spot, but away from direct sunlight. "Depending on the type of plant, it should start to form new roots in a couple of weeks," says Jabbour. "Gently tug on the cutting after two weeks, and if you feel resistance, it's likely rooted." Gardeners can continue by transferring rooted cuttings to containers of potting mix and harden them to prepare them for outdoor growth.

Perlite vs. Vermiculite

Another mineral often compared to vermiculite is perlite, a mined underground volcanic rock. "Perlite is also heated before it's used in horticulture with the resulting material often compared to little balls of styrofoam," says Jabbour. "Perlite is the white, often spherical, particles we see in potting mixes."

Perlite's surface allows water to set in, which allows for added moisture to plants. Lightweight perlite is often used in potting mixes to help aeration and drainage.

When to Use Perlite vs. Vermiculite

Perlite and vermiculite are both used in potting mixes—and both minerals can be used to root cuttings. Perlite is better for propagating plants, since it's more lightweight, says Jabbour. However, she uses vermiculite for seed starting, as this mineral is easier to add to the soil surface. "Plus, it holds moisture, which most flower and vegetable seeds need to prompt germination," she says. No matter which material you use, Jabbour recommends wearing a mask when working with these minerals, as they are both dusty.