What’s the Difference Between Potting Soil and Potting Mix?

Have you stood in the soil aisle of a garden center lately? Why does every bagged product have a variation of the same name? Take potting mix and potting soil. They sound similar to me, and I’m a fairly experienced gardener. But I spend most of my time outside, where garden soil and topsoil reign. Good grief, even those sound identical!

If you’re confused about potting mix and potting soil, we’ve got you covered. “Choosing the right potting medium will make all the difference for a plant,” says Lisa Eldred Steinkopf, known across the web and in her many books as The Houseplant Guru. She knows her stuff, and she’s here to help. For good measure, we also consulted Tony Provin, Ph.D., a soil scientist and professor from Texas A&M University extension.

Read on to learn all you need to know about potting mix and potting soil.

What is Potting Mix?

Potting mix is a “soil-like” planting medium that doesn’t actually contain any soil, Eldred Steinkopf says. “It anchors the plant and provides water and nutrients to the plant through its root system.” Potting mixes can be tailored to different plants, such as African violets or succulents, and “they may contain peat moss, coir, vermiculite, perlite, bark ash, sand and bark.” Potting mixes are typically sterile, which makes them excellent for seed-starting and indoor gardening, Eldred Steinkopf says.

If some of those ingredients aren’t familiar to you (coir, for example, is a fiber from coconut husks), Provin says the ingredients in potting mixes are bulking agents used to prevent heavy water saturation. That makes potting soil lighter and easier to handle than potting soil, a major bonus when filling flowerpots. “The [lighter] weight alone would be the number one thing [that appeals to gardeners],” Provin says.

What is Potting Soil?

Potting soil is soil enhanced with enrichments like compost and peat moss. Soil is the layer of the earth that supports plant life, and it naturally contains various broken-down organic matter from plants and animals, as well as minerals and microorganisms. Potting soil is denser and heavier than potting mix. Provin says you’ll definitely notice the difference if you’re trying to pack multiple bags of potting soil into the back of a Prius!

Because soil is dug out of the ground and contains the remains of long-lost organisms, it’s not sterile. That’s why it’s best for outdoor use, Eldred Steinkopf says. And while potting soil is formulated for outdoor pots and raised beds, it’s okay to use it right in the ground. Don’t confuse potting soil for garden soil or topsoil, though. These soil-rich media should not be used in pots without amending for drainage and nutrients.

When Should You Use Potting Mix vs. Potting Soil?

In general, potting mixes are best for containers, both indoor and outdoor, and seed-starting. Today’s potting mixes are specially formulated for various plants and uses, so it pays to do your homework. “If you are starting seeds, it is best to buy a seed-starting mix that is developed for optimal seed germination and growth,” Eldred Steinkopf says. “For your indoor plants, there are potting mediums for African violets, cacti and succulents, orchids and all-purpose mixes.”

Save the potting soil for outside. “The key difference is the presence of soil, and I would use that only outdoors,” Eldred Steinkopf says. Another thing to think about is the price. Potting soil is more expensive than garden soil, which is more expensive than topsoil. Potting mixes are the priciest of all. So, while you can fill a 6×6-foot raised garden bed with potting soil, you’ll be out a pretty penny. “Don’t be afraid to take soil and amend it, to meet in the middle [between potting soil and potting mix],” Provin says.

Same thing with houseplants. “I add amendments such as perlite, vermiculite, pumice, or orchid bark to make the mixes better for the plant I have,” Eldred Steinkopf says. “That is a personal preference and something learned from experience.” Many potting mixes contain fertilizer and a substance that retains moisture, but Eldred Steinkopf prefers to avoid those additives so she can make the medium her own. You can do the same as you gain confidence with indoor or outdoor gardening.

About the Experts

• Lisa Eldred Steinkopf is The Houseplant Guru and author of multiple books on houseplant care. She is regularly featured in publications across the web and in speaking engagements, where she shares her love and knowledge of all things houseplant.
• Tony Provin, Ph.D., is a professor and extension specialist at Texas A&M University, where he is the director of the Soil, Water and Forage Testing Laboratory.