The line between soil and hydroponics can seem a bit muddy (pun intended). The exercise of defining it may sound trivial, but it helps us to think through what the critical, differentiating characteristics and benefits are, as well as the drawbacks, for soil and hydroponic approaches to growing.
Here's a definition for soil:
noun: soil
the upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles.
"blueberries need very acid soil"
synonyms: earth, loam, dirt, clay
Here's a definition for hydroponics.
noun: hydroponics
the process of growing plants in sand, gravel, or liquid, with added nutrients but without soil.
Notice the end of the definition! - "without soil"
There are a lot of soils to choose from out there with recipes including a range of organic and inorganic ingredients. The same can be said about hydroponic media, which can range from literally nothing in aeroponics, to hydroton clay pebbles, to organic material like coco coir.
Here's a definition for soil:
noun: soil
the upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles.
"blueberries need very acid soil"
synonyms: earth, loam, dirt, clay
Here's a definition for hydroponics.
noun: hydroponics
the process of growing plants in sand, gravel, or liquid, with added nutrients but without soil.
Notice the end of the definition! - "without soil" ...not very helpful!
There are a lot of soils to choose from out there with recipes including a range of organic and inorganic ingredients. The same can be said about hydroponic media, which can range from literally nothing in aeroponics, to hydroton clay pebbles, to organic material like coco coir.
We’ve seen all of the ingredients used in the definition above for hydroponic soil but none of them all together. Would combining them suddenly transition your hydroponic system to a soil garden?
As with most things, there probably isn’t a black & white answer, just a big range of grey.
Personally, I like to think about it from a practical stance that would inform deciding between using a hydroponic setup vs a soil setup. What I see as driving this decision is nutrient availability and control. Soils contains nutrients that are available to the plants, while hydroponic media do not. Under this scope, nutrients are added to supplement, improve and replenish depleted soils.
Yet, with a hydroponic system, the nutrients available to plants were added to the system in a water solution and did not come from the media. This allows for hydroponic growers to have more precise control and the ability to make rapid significant changes. Unfortunately, rapid and significant changes in hydroponic systems aren't always intentional, and when they aren't, it usually isn't a good thing.
So, what’s your definition of soil? Is it about nutrient availability or something else?
Relevant Resources:
http://www.dictionary.com/browse/hydroponics
http://www.garden.com/garden-articles/what-is-dirt-made-of-anyway/63/