Water as a substrate
By Noucetta Kehdi
“Aeroponics”, “Aero-hydroponics”, what does it all mean?
When choosing a hydroponic system, one of the important factors to keep in mind is substrate. Today there is quite a wide variety offered to the soil-less gardener. Among the most common are rock wool, clay pebbles, coconut fiber, several peat mixes, lava rock, perlite and vermiculite. Of course it is important to choose the best adapted to your growing method (see “Substrates” in Spannabis N° 3).
But do you really need a substrate? In fact, what does the substrate do? What is its action?
There remains a misconception among growers that attributes to substrate alone the task of setting up the relations of air and water with the root system of their plants. In reality the role of the substrate is about 15% in the plant’s growth, the other 85% being in the hands of the grower himself.
A substrate is the media in which a plant can grow. It generally is one, or a combination of materials, that provide support, aeration, plus water retention and distribution to the plant. Basically, as far as the plant is concerned, substrate must hold water, oxygen, and nutrient supply, drain correctly, and stay neutral so that it does not interfere with the plant’s development.
For the grower, the substrate must respond to several other factors: it needs to be dependable, economical and light. It must be easy to handle – and easy to dispose of ! Ideally it should be non- polluting and biodegradable. And if you are a perfectionist, it might even have to be natural.
Some find all these parameters too tedious to depend on. So the next question is to ask how necessary is substrate then? Can you do without it or can you at least reduce it to the minimum?
This is where Aeroponics and Aero-hydroponics come into the picture. These technologies respond exactly to these issues, and solve them in no time: no substrate anymore, or hardly any! No more carrying bags up the stairs, no more dumping loads of used material to the rubbish, no more substrate related pests and diseases, no more weight to clean and move around.
But then what is Aeroponics and what’s Aero-hydroponics?
Have you ever seen growing systems that mist the solution at the root level in a fog form? These would be Aeroponic systems, a technique were water is delivered to the roots as a high-pressure fog. This technique is not often used in its pure form. Although some companies like to call their systems “aeroponic” systems, you will generally find them only in research laboratories and universities.
Aeroponics has its advantages and its inconveniences. It saturates the nutritive solution with oxygen, which gives the plant’s roots the healthiest of environments. Its most interesting application is plant propagation. But if you want to keep the crop all the way to maturity, you will notice that the root zone will develop too fast and too much, at the expense of the aerial part of the plant. This is not what we are generally looking for … except in the case of root crops. And even then, it is not always practical because the roots often stay soft from being immersed in water, and won’t offer the firm characteristics needed, like for instance in the case of liquorice.
Aero-hydroponics is an adaptation of aeroponics. It really started in the mid 80s in California, where Laurence Brooke decided to bring aero-hydroponics into the mainstream market. He started with the “EGS” (Ein Gedi System), a unit invented at the University of Davis in California, which was used essentially to study the content of oxygen in water, and transformed it into one of the best propagation systems known up to now, the “RainForest”. This unit will spew out mist to the roots, not in the form of a fog system, but rather as a “vortex” spray. Today there are loads of aero-hydroponic growing systems on the market, some very efficient, some less, depending on the experience and the know-how of the manufacturer. You can even build your own with a little help from the many magazines and books you can find in “hydro” shops.
In Aero-hydroponics water fills with oxygen through different methods: spray, injection, cascade. It relies on a pump pushing water through different sprayers and irrigation tubing, and falling back down into the reservoir. A well-conceived aero- hydroponic system must offer a good balance among its different components, and proper ratios between the different flows of water and the shapes of its different components (tubes, reservoirs, sprayers and irrigation devices).
Both aeroponics and aero-hydroponics need no, or hardly any substrate. They use only plant supports in the shape of coconut pots, plastic net-pots, or just neoprene rings, and leave you with only water as a substrate.
Indeed, now the game is into the water, and in the gardener’s hands altogether. One thing you know is that you have eliminated the most “gruesome problems” of substrates, but you may wonder if you have switched to others … maybe as difficult to address? No, not really. To eliminate safely the traditional substrates, what you must ensure is water availability to the plant, good aeration, and a neutral environment. In aeroponics and aero-hydroponics, this is “basics”: perfectly well oxygenated water is presented to the roots and drainage is ideal.
Once this said and done, the rest is, once again, in the hands of the grower. He must ensure a well-balanced and comprehensive nutritive solution, a correct level of EC and pH, good ventilation, temperature, humidity, and cleanliness, as you would generally do for any plant, and any other growing technique.
Some people may think that aero-hydroponics is a difficult technique, and they may be right to some extent. The only real advantage of substrate is its buffering capacity: which means that contrary to water, where parts of your roots hang bare in the air, the substrate will surround the root zone completely, and thus protect it from environmental variations like temperature or humidity, or any “accident” that may happen. This is why it is often recommended that a beginner starts with “substrate-using” systems and switch to aero-hydroponic systems once they have acquired a little more experience. Some manufacturers will offer “dual” growing units, with special kits that allow you to switch from one “susbtrate-using” machine to a “no substrate using” machine, as soon as you feel more confident. And they will guarantee fast and free technical advice and follow up to their customers.
You can even choose aero-hydroponics as a beginner, if you wish. Just follow the instructions that come with your growing unit, and you’ll see how simple it is. And don’t forget that, whichever technique you choose, it is not the system nor the fertilizer alone, but the gardener who ensures the plant of a healthy development.
A few weeks ago in Berlin, I had the good fortune, and the pleasure, to meet Melchior, from High Five in Holland. As most Dutch growers, he used the traditional rockwool and drip system, and was quite happy with it. Last year, an Australian friend of his left him with a small aero-hydroponic system, a small replica of the “AeroFlo” systems. Melchior “played” with it for a few months and was definitely persuaded. His plants looked perfect, uniform, and harmonized. His harvest was great, much better than any other he had in years – and he is a qualified, experienced grower. One of his biggest satisfactions is not only the excellent yields he achieved, but the fact that he was ridden from substrate and all the hassles related to it. Today Melchior is the first Dutch distributor to introduce aero-hydroponics to the Dutch market. Let’s see what these excellent growers will accomplish with it!