Ingeniero

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 fibre, several peat mixes, lava rock, perlite and vermiculite. Of courseit 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 thesubstrate 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, draincorrectly, 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 nonpolluting and biodegradable. And if you are a perfectionist, it might even have to be natural. Some find all theseparameters 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 dumpingloads 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 notoften 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 firmcharacteristics 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 oxygenin 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...