Soil vs. Dirt: What's the Difference?

It may be pedantic to point out the difference between "soil" and "dirt." The dirty little secret is that there have been farmers and gardeners for centuries successfully growing plants in what they may have incorrectly called "dirt." They may have gotten the terminology wrong, but they were right where it counts: the end product. Nonetheless, for purposes of learning, it can be useful to draw such distinctions: In the process of getting the terminology right, you will absorb information that is useful in becoming a better gardener.

Here's what to know about the differences between soil and dirt, and how other media used to grow plants differ (and why one will be better than another in particular situations).

Are Dirt and Soil the Same Thing?

Dirt and soil are not the same thing, but they are certainly related. The easiest way to remember how the two are different and yet related is to think of soil as having dirt in it, while also having extra things in it that make it superior to mere dirt. You can't have soil without dirt, but if soil loses those "extra things," it degrades back into something less useful: dirt.

What Are the Components of Dirt?

The dirt in your soil is primarily composed of three types of particles: clay, sand, and silt.

You have probably heard these terms used in connection with soil types. What makes a particular soil a "sandy" soil, for example, is not that it's just sand (the other two particles are probably present, too) but that the percentage of sand is relatively high.

Clay, sand, and silt are all nice things. It's just that the dirt they form is insufficient, on its own, for growing plants.

What Are the Components of Soil?

So what is added to a soil's mere dirt to make a suitable medium for growing plants? Essentially, it is life. Clay, sand, and silt particles are great and offer nutrition potentially, but they lack life. On a more scientific level, we can say the problem is that plants have trouble accessing this potential nutrition in its raw form; it has to be unlocked. It is living creatures in the soil (mainly microorganisms) that unlock the minerals and make them accessible to plants. That's one reason why gardeners add organic matter to their soil: These indispensable microorganisms live in organic matter. 

So, soil is made of dirt (clay, sand, and silt) plus organic matter teaming with life.

Soil, Potting Soil, and Potting Mix

Another distinction to draw for beginners to aid in their horticultural progress regards products used as planting media that have "potting" in their name. This is a confusing topic for beginners because the green industry often slips into imprecise language and uses what should be two distinct terms interchangeably.

Potting soil and potting mix are both different from "soil." But they are also different from each other.

Potting Soil

It would make more sense for retailers to call potting soil "garden soil," because consumers are better served using it for in-ground gardening and for filling up large raised beds than for potting up plants. Potting soil is designed to be very close to a good natural soil. It's essentially a natural-soil substitute for those who lack healthy soil on their property and/or need soil in a hurry for a garden project and don't mind paying for it. Like regular soil, potting soil is made up of dirt and organic matter (often compost).

Potting Mix

Potting mix, by contrast, does not contain soil or dirt. In fact, people often call it "soilless potting mix" to drive home the point and minimize confusion. Ingredients of a typical potting mix would be:

• An organic material such as coir
• Components that improve drainage (in addition to offering other benefits) such as perlite and vermiculite
• Slow-release fertilizer

The result is a medium fluffier than soil and perfect for growing a variety of plants in a container such as a whiskey barrel or potting up individual plants. Since it is relatively sterile compared to soil, it is also great for starting seeds.