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Soils 101: Why soil, not dirt?

Why is it that people like me (Doug) get bothered when someone refers to soil as “dirt”? Are there grounds for this minor irritation? (Perhaps.) Is it fair to expect those new to the world of gardening and the great outdoors to differentiate between two apparently synonymous words? (Probably not.) Let’s dig in and take note of the differences in the meanings of these two words. 

Let’s start with what natural soil actually consists of. An average soil is made up of: 

  • 45% mineral matter (sand, silt, and clay particles), 
  • 5% organic matter (decomposing stuff, microbes, earthworms, etc), 
  • 25% water 
  • 25% air (in other words, 50% pore space fluctuating in the amount of air or water depending on the most recent rain or irrigation event).  

The combination of these components creates a dynamic living environment that is ideal for growing plants. Native or natural soils are considered to be renewable. However, in colder climates it can take around 1,000 years to develop just one inch of new topsoil, while in warm humid climates it “only” takes several hundred years. 

Dirt on the other hand, or either hand, is actually just the mineral matter–sand, silt and clay particles, that gets under our nails, messes up our shoes and gets on our clothes. These particles by themselves are not a living environment; therefore, they are just dirt. 

Soil Graphic
Comparative particle size of mineral matter: sand, silt and clay.

So, there you have it, the difference in soil and dirt is that soil is a dynamic living environment because of all the components that it consists of, and dirt isn’t.

The “soil” most of us use in our raised beds is not natural soil, but is a combination of largely organic, and some mineral, components. Compost is often one of the primary components which can be derived from dead plant material or some form of animal manure–from worm castings to horse manure. A good growing media can be created for raised beds using these components. We often loosely call these mixes “soil,” but in fact they are not “true” soil, but rather are a suitable substitute for the real thing. What is natural to the earth is the only real soil. You may even hear of different substrates that are defined as soilless growing media.

With the development of microbe populations in the soil and building soil with regenerative practices such as cover crops, we can improve any soil or growing media, natural or not. And, with additives such as organic fertilizer or vermicompost, we can grow beautiful bountiful crops of all kinds, in soil, not dirt.