The first and most important disadvantage is that the plants are not protected from your mistakes. Soil has a buffering capacity, which provides a certain stability around the root mat. In healthy soil, all the physical and biological parameters are in balance. If you give your plants too much nutrient, a wrong mix, or something with the pH completely off, the micro-organisms in the top soil as well as the soil chemistry itself will tend to reestablish equilibrium. This happens also in hydro, but only to a limited extent. The nutrient solution has some buffering capacity, especially in terms of pH, but nothing comparable with soil. Something as trivial as a pH meter off scale can have dire consequences, such as killing your entire crop in a day.
Things happen fast in hydro
An image that I like to use is the comparison between driving a race car and driving your family car. At the wheel of a race car, you go much faster, but an accident is likely to have much worse consequences. Growing in hydro is the same. It goes so fast that you can literally see the plants grow… but you can kill them in one hour. Temperature is also a limitation. 18°C to 22°C in the root zone is the range at which plants grow best in hydro. They can tolerate much more. Up to about 26°C nothing happens, then growth slows down, and at around 35°C their roots, lacking dissolved oxygen, start dying fast, and so do the plants.
There are means of fighting the heat that we will see later ; nonetheless, it is a severe limitation, especially in tropical countries and indoors, where artificial lights generate a lot of heat. Another limitation is that you cannot grow every crop in hydroponics. All the roots or tuber crops, such as carrots or potatoes; everything that is harvested from inside the ground, require very special systems. The economics of a crop are also a limitation. For instance, wheat would grow well in hydro but this would not be economically feasible. The geographical location, as well as the local market, will determine which crop is feasible to grow and which is not.
There are other criticisms I often hear when I talk with people on the subject of hydro. The two main ones are that it is expensive to initiate, and it is unnatural. I even have heard the expression “plants on a drip”, used in its medical sense. It is true that hydroponics systems have a cost that can be steep, but in indoor cultivation you rapidly recover the money you spent. The reason is simple: electricity is expensive. When you grow plants under lights, you want to harvest your crop as fast as possible because the total usage of electricity, between the lights and climate control, is significant, even for the smallest growing operation.
The faster you get your harvest, the lower your production costs
Hydroponics saves time, and a lot of it. In this case time is really money. As for unnatural, I find this also debatable. After all, what is natural? Is planting an entire field with a single plant “natural”? Nature is diversity. Think about it; by definition all forms of agricultures are “unnatural” practices, strange as that may sound. When humans were still at the hunter/gatherer stage, our impact on the planet was nearly nil. Like all other living organisms, we would take our food from our environment, but we did not modify it very much most of the time. The problem started when we passed on to the agricultural stage, when we started to plant crops in fields. This allowed man to change from a nomadic life to a sedentary one. Soon the villages became cities, then cities-states, fighting with each other for more land, and that led to the civilization that is ours today.
All of today’s problems can be traced back to the first man who planted a field.
Hydroponics with its plastic tubes and mineral salts might seem weird at first sight, but at the end of the day, it is no more or less unnatural than agriculture itself. Strangely, people don’t seem to mind using mineral salts to feed their house plants in soil. They do it recklessly, with the risk of nutrients ending up in ground water or the city sewer. Conversely, they seem to mind using those same mineral salts, in an even purer form, in the safety of a plastic gutter.
They would resort to foliar feeding, not very common in nature you must admit, but they see roots bathing in a nutrient solution as unnatural. There are many islands where the land cannot feed the large tourist population, tropical countries where the soil is full of hungry pests, places where the land has been so abused that it has lost most of its fertility, places with no arable land at all.
Everywhere that organic cultivation cannot be the only option, hydroponics could be one of the solutions to feed a hungry world without destroying our environment. It is a type of agriculture that can provide man with nutritious and delicious produce as well as medicines in places where it would be impossible otherwise. Its level of “unnaturalness” is irrelevant.