Soil vs. dirt — what’s the difference?

In the farming and gardening community, the brown stuff your veggies are planted in is referred to as soil, not dirt. But when you spend a long day gardening and wash it off your hands at the end of the day, we call it dirt.

So is there really a difference?

Soil vs. dirt

While we may consider the same material to be soil in one circumstance and dirt in another, the connotation is important.

Soil is nutritious, life-giving material for plants, and is also full of microorganisms, insects, organic matter, and bacteria. 

What is soil made out of?

Soil is composed of four types of materials: sand, silt, organic matter, and clay. The composition of soil varies from place to place and impacts things like the texture and nutrients of the soil, as well as drainage and aeration. 

What is dirt made out of?

So if soil becomes dirt when it is displaced (for example when you spill it from your planter or wash it off your hands), what is dirt made of? Really, it’s made of the same materials as soil, but it has left its natural ecosystem. The important bacteria and microorganisms are likely to die off without the rest of the ecosystem, and it doesn’t hold its structure like soil does.

So, dirt is essentially soil that is dead. 

Why are there so many different types of soil to choose from at the store?

Surely you’ve been to Home Depot to see twenty or more types of soil that you can buy to use in your garden. So if soil is living and dirt is dead, what’s the difference between topsoil, potting soil, and so many other variations?

Typically it comes down to the specific blend of nutrients provided in the soil and the texture of the soil. Many bagged soils will specify what types of plants they support — veggies, flowers, or even cacti. They have been formulated specifically with the nutrients that that type of plant needs, and are a great option for potting soil.

Topsoil

Topsoil generally refers to the top layer of soil on the ground (duh!) It contains ground-up rocks, clay, and organic materials. Topsoil tends to be heavier, denser, and retain more water, so it’s not always the best option to buy for healthy plants, especially things that will be living in planters. It is also usually devoid of the healthy microbial behavior that your plants need.

Potting soil

Potting soil is lighter and fluffier soil, specifically blended with nutrients to support plant growth. Some potting soil also contains vermiculite or perlite, which contain nutrients and help with water retention.

Seed starting soil

Seed starting soil is a particular kind of potting soil, and will typically be sold in smaller bags. It is designed to provide maximum nutrition inside of a container for growing seedlings. 

When you should use topsoil vs. potting soil

It can be tempting to grab the topsoil for everything because it tends to be a lot cheaper, but using topsoil for gardening will rarely yield positive results. It is great to use to fill large spaces or to use for planting grass. If you have tall gardening boxes to fill, you can include topsoil in the lower levels to help take up space, but be sure to incorporate a lot of organic material in the higher levels of the soil where your plants will live.

In most cases for indoor plants, you will want to use potting soil. You might also incorporate potting soil into garden bags or large raised beds to ensure there is enough drainage and your plants are getting enough nutrients. Choose the right kind depending on what you need — seed starting soil, soil for a particular type of plant, etc.

So really, displacement is the difference between soil and dirt: soil is living in its own ecosystem with thriving bacteria and organisms, and dirt has been removed from its ecosystem and is essentially dead.