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  Why Aeroponics?
by Dr Lynette Morgan

Aeroponics is a growing method where the plant roots are suspended in the air with a fine mist of nutrient solution applied either continually or intermittently over the root surface. While we tend to think of aeroponics as a recent development in the hydroponics field, it has actually been in use since the 1940's, although largely as a research tool rather than as an economically feasible method of crop production. In the last decade however there has been the development of a number of aeroponics systems both for use commercially and as small 'hobbyist' systems. The reasons for the interest in aeroponic technology stem from the fact that using traditional hydroponics systems (media, NFT and flood and drain), has often made controlling conditions in the root zone difficult, particularly where growers are battling a tropical climate. And for this reason much of the large scale commercial development of aeroponics has occurred in countries such as Singapore where temperate crops such as lettuce and other salad greens can be successfully grown using aeroponics technology where other hydroponic methods failed.

For the smaller hydroponic grower, aeroponics offers other major advantages: Oxygen starvation, stagnation and water logging and over watering are common problems in hobbyist hydroponic systems and many plants have been lost to these causes without the grower even being aware of what is happening. It can be difficult to supply the plant's root system with sufficient oxygen, particularly in warmer conditions where the plant's oxygen requirement is much higher and less dissolved oxygen is held by the nutrient solution. Aeroponic methods ensure the plants not only have sufficient water, nutrients and of course oxygen, but the temperature inside the root chamber can be easily controlled, ensuring temperature stress of the plant does not limit growth. For this reason, the use of a well designed and maintained aeroponic system can give huge increases in growth rate and plant survival when compared to many of the standard NFT or media based hydroponic systems.

How Does Aeroponics Work
With an aeroponic system the young plants can be either raised as seedlings using especially designed lattice pots or cuttings can be placed directly into the aeroponic system for rapid root formation. Lattice pots allow the root system to develop down into the aeroponic chamber or channel where it is regularly misted with nutrient. There is a high success rate with plant cuttings which are rooted in aeroponics - in fact this method has been extensively used as a research tool into root development on many difficult to propagate plant species. The base of the cutting is supplied with high levels of oxygen and moisture in a humid environment which prevents desiccation and accelerates root formation.

Once the young plant has been established into the aeroponics system, the root system rapidly develops in the chamber or channel. What is important at this stage is that the optimum size of the droplets is maintained within the system for maximum efficiency. There is a huge range of aeroponic nozzles so selection of a droplet size range which best suits the plant and system used is fairly easy. Spray droplets less than 30 microns tend to remain in the air as a 'fog' and are not readily absorbed by the roots. The ideal droplet size range for most plant species is 20 - 100 microns. Within this range the smaller droplets saturate the air, maintaining humidity levels within the growth chamber, the larger droplets 30 - 100 microns make the most contact with the roots, while any droplets over 100 microns tend to fall out of the air before containing any roots.

Misting Frequency and Nutrient Reservoir
Aeroponic systems may mist the root system continuously, or intermittently and both methods work well, since water logging and oxygen starvation are not a problem in aeroponics. The major advantage of intermittent aeroponics systems is the saving in running cost, since the pump is only on for a short period of time, but the roots are still contained within the nutrient, moisture and oxygen rich environment between mistings. And since aeroponics systems do require larger pumps with greater energy requirements than other hydroponic systems, this saving is an important feature. Always look for systems that either link light levels to misting frequency or have the ability to program in a large number of misting cycles per 24 hours. As a general rule, a misting cycle of 1 -2 minutes of misting followed by 5 minutes off will ensure the root system does not dry out under most conditions.

Aeroponics systems are further divided into those which have a separate nutrient reservoir and pump the nutrient up into the root chambers and those with an all in one' contained chamber and nutrient tank. The simpler aeroponic systems spray the nutrient up from the reservoir in the bottom of the root chamber, where it drips back down after misting the root system. By the time the plants are mature, the root system has often grown down into the nutrient solution stored in the base of the chamber and blockages can occur. Larger aeroponic systems return the nutrient after misting to a separate nutrient reservoir.

The Importance of Filtration, Light and Pressure
Obviously if a mist of the correct droplet size is to be produced and delivered to the plants, a certain amount of pressure is going to be required - so larger pumps are required in aeroponics systems than would be used in NFT. In order to maintain this pressure, filters need to be kept clean, nozzles free from salts, debris and algae and pumps well maintained. Another important aspect is to ensure the aeroponic chamber is light-proof, growth of algae soon results in blocked nozzles and needs to be avoided. Both inline filters and pump filters assist with removing any particles form the nutrient which might block nozzles, and having sufficient pressure will also assist in keeping nozzles clear and function correctly.

Nutrients
With aeroponic systems the same inorganic nutrients and methods of EC and pH measurement can be used as in other hydroponic systems. However, extra care needs to be taken with certain 'additives' - particularly those which are organic in origin. These sometimes contain tiny particles of suspended solid matter which doesn't cause problems in NFT or media systems, but can block the aeroponic nozzles or jets.

Temperature Advantages
If you are constantly battling an overly warm or cool growing environment, aeroponic technology can allow the production of plants which would normally not thrive under certain conditions. By heating or cooling the nutrient before it is misted into the root zone, the temperature inside the growing chamber (which needs to be insulated) can be precisely controlled. Depending on how extreme the aerial environment, it is possible to grow crops with nutrient solution warming or cooling only in aeroponics, something which is more difficult to achieve in other hydroponic systems where the solution rapidly cools/heats as it flows through the system. In Singapore, by cooling the aeroponic solution by 10 - 15C below the ambient air temperature, cool season crops can be grown within modifying the temperature of the aerial environment. While this technique is still be investigated it is worth experimenting with on a small scale if hot/cool temperatures are a problem in your growing environment.

What Can Go Wrong with Aeroponics
While the incidence of root diseases is much less common in aeroponics, since oxygen starvation and root damage don't tend to stress the plants, these can still occur. One of the most important aspects to remember is to check the temperature of the nutrient solution in a regular basis. Plant roots can become stressed if root temperatures are too high/low, resulting in root death and the opportunity for pathogens to attack. Keeping a close check on the appearance of the root system is important. Roots which are thin, brown and lack the fine 'root hairs' indicate a problem and often indicative of a nutrient solution which is too warm. Nutrient solution temperature should not exceed 72F for most crop plants or 68F for cooler season crops such as lettuce.

Grower Ability
While building your own aeroponic system is not difficult, it can be a prolonged trial and error process. Aeroponic chambers have to be completely water tight, light proof, large enough to contain a mature root system, well designed to ensure good mist coverage and have a support system for the plants. The equipment required to run the system can be confusing - selection of nozzles with the correct droplet size and a pump with sufficient pressure to run the system are vital to the success of the aeroponics unit. Fortunately there are a number of excellent small aeroponic systems on the market where all the correct components have been put together into a workable (and leak proof) system, and purchasing one of these is a good way to become familiar with aeroponic technology before bigger projects are planned.

Running the aeroponic system is no more difficult than other hydroponic methods. The one important rule with aeroponic systems is regular checking and maintenance. If one of the nozzles becomes blocked or the pump fails for any length of time, the plants can rapidly desiccate as there is no reserve of moisture as would be found in a media based system. Tiny particles of nutrient salts, or vegetative matter often block nozzles in many aeroponic systems, so regular checks inside the chamber are important.

Perhaps one of the major attractions of aeroponics is the ability to watch the root system grow and develop - plants can be removed from the system and inspected for root damage, diseases, and with crops such as gourmet potatoes being grown in such systems, the process of tuber promotion can also be viewed. Aeroponic technology is progressing at a rapid rate, not only is this an easy to operate system of hydroponics but it has the potential for faster growth rates and higher yields than most traditional methods of plant production.

Click here to view Pipe Dreams Aeroponic Systems!