Soil supplies nutrients and water that plants need to grow. According to the Soil Science Society of America, there are 22,000 different soils in the U.S. Calling it “dirt,” which so many Americans do, is a serious misnomer, even if most people know what you mean. But how does this affect potting soil and potting mix?
While some sources maintain that potting soil is garden soil and very different from potting mix, this is not true. Instead, supposed differences come from a perception that has created a multitude of definitions. Many of these boldly show how potting mix differs from the potting soil. But, in reality, potting soil and potting mix are both potting materials that contain a mixture of ingredients.
What is potting soil?
It stands to reason that potting soil is suitable soil that we use for potting plants. If you have good quality topsoil in your yard, you might consider using this instead of store-bought potting soil.
As the Soil Science Society points out in a PowerPoint presentation, Getting the Dirt on Soils or Why is Soil Important, topsoil is the most productive layer of soil. But it can take more than 500 years to form one inch of topsoil.
So, there’s no guarantee that you will have good-quality garden soil. If you have recently built your home, you may also find that during the construction process, much of the valuable topsoil was removed by construction workers. It happens all the time!
Also, there are three basic types of soil that make up the 22,000 different soil types the Society mentions. These are sand, silt, and clay. And different plants do better in some types than others.
An important caveat is that, in general, garden soil tends to become compacted and saturated with water. It isn’t pasteurized, so it also becomes an ideal environment for weeds, disease organisms, and insects.
When we buy commercially produced potting soil for our plants, we have the opportunity to pick and choose according to what particular plants like the most.
Different types of potting soil
Whether you shop for potting soil online or at your local garden center, you will find that there are different types of potting soil. For example, FoxFarm Ocean Forest Potting Soil contains bat guano, earthworm castings, and all sorts of micronutrients.
FoxFarm calls it “organic” and says it has a light texture and is well aerated. It is ideal for “containerized plantings,” i.e. potted plants.
Hoffman produces a Purely Organic Potting Soil that they refer to as a “potting mix soil conditioner.” It is intended for repotting plants, outdoor containers, hanging baskets, and window boxes.
They say it contains a “wetting agent” that maintains moisture in the soil for longer. This means that you don’t have to water your potted plants as much.
Wetting agents are chemical substances that lower the surface tension of the soil. Yucca extract is one type of wetting agent used for organic soil mixes.
Of course, the fact that bagged potting soil contains various additives means it’s a bit of a mix. But then, when we want to improve our garden soil, we add things like compost and other soil amendments, including fertilizer.
Sometimes potting soil is labeled for in-ground use, meaning it’s intended for use in your yard. While it’s bagged, it mimics the components of natural soils including various mineral elements, for instance, Miracle Gro’s garden soil for vegetables and herbs.
Just remember that neither garden soil nor potting soil is, or contains “dirt.” We’ll let the Soil Science Society of America have the last word here.
Soil does not equal dirt! “Dirt is the stuff under your fingernails or that you sweep off the floor.”
What is a potting mix?
Potting mix is a bagged mix of materials suitable for potting plants. Commonly, potting mixes contain zero soil.
Tina Smith and Dr. Douglas Cox of the University of Massachusetts Amherst Extension explore Bagged Potting Mixes and Garden Soils for Home Gardeners in an online article. Here they state that potting mixes, which are also known as soilless media or compounds, usually comprise combinations of coir, peat moss, perlite, pine bark, and vermiculite.
At the same time, many people use the term potting mix to describe potting soil. And indeed, some manufacturers use the terms soil and mix in their sales descriptions.
For example, Expert Gardener markets an “expanding soil concentrated potting mix.” Dr. Earth markets a premium, organic, all-purpose “potting soil” that is an all-purpose indoor and outdoor container “potting mix.”
Sungro’s Black Gold All-Purpose Potting Mix is described on Amazon as an all-purpose potting soil. But the description also states that it is a “slow-release complete fertilizer” that is made with sphagnum peat moss with worm castings, forest humus, and pumice.” No mention of soil at all!
This company’s Natural & Organic Potting Mix Plus Fertilizer is also described on Amazon as an “all organic potting soil.” This, though, is a “rich, loamy mix,” which implies that it contains loam (fertile soil). It also contains perlite and pumice.
Espoma’s organic potting mix is intended for all potted plants. Ingredients include alfalfa meal, earthworm castings, feather meal, kelp meal, and Myco-tone, which results in an “all-natural potting soil.”
It’s enough to confuse anyone.
What is the difference between potting mix and soil?
If you consider the examples of potting mixes and potting soils we have mentioned, you will see that there are different types of potting soil and different potting mix blends. But, let’s get back to the question, Is there a difference between potting soil and potting mix?
In a broad, ambiguous way, you could be forgiven for saying that potting soil and soilless potting mix are different. It stands to reason that they would be because a soilless potting mix doesn’t contain soil.
But some potting mixes clearly do contain soil.
Additionally, there are many different soils and potting mixes that are produced specifically for certain types of plants. You will find:
- cactus and succulent soil mix
- cactus, palm, and citrus mix
- houseplant potting mix
- African violet potting mix
- professional aloe plant soil
- orchid potting mix
- raised bed soil
… and more.
You will also find a seed starting mix that is even lighter and better aerated than any other type of soil mix. Jiffy brand’s seed starting mix is made with Canadian peat moss.
Espoma has a seed starter for all potted plants made with 80-90% Canadian sphagnum peat moss, perlite, yucca extract, and limestone added to adjust the pH of the mix.
If you can’t find exactly what you want and need to retain water in potting soil, you can use perlite, vermiculite, or even sand. Perlite and vermiculite are not the same, but they both have a neutral pH.
Ultimately, it makes more sense to compare garden soil with potting mix rather than so-called potting soil.
Can I mix potting soil and potting mix?
There’s no real reason you shouldn’t mix potting soil and potting mix since they are often much the same. One time might be when you want a soilless growing medium.
When you embark on a discussion that involves the differences between potting mix and potting soil, you’ll be faced with a multitude of ifs and buts. It’s much the same as trying to compare apples with apples, which is virtually impossible.
A common difference between potting soil, potting mix, and starting mix is that potting soil is often the only medium that contains soil. But it gets complicated because this is not always the case.