When investigating the specifics of aeroponics, you may see some conflation between hydroponics and aeroponics systems, specifically with regard to the roots’ access to the nutrient solution. In true aeroponics, roots are suspended entirely in air and should never reach all the way to a pooled nutrient solution. Not only does this limit the oxygen that particular portion of the roots are able to absorb, but this kind of growth is wasteful and indicates that the plants are not getting adequate water/nutrients from the misting/spraying system. In a properly balanced system, plants will focus on growing bushier and more abundant roots which accelerate growth and production, rather than growing long roots just to reach the solution. In those situations, the growth rate and production of the crop suffers.
The unique value of aeroponics is a plant’s ability to easily absorb water and nutrients coupled with its ability to use those resources to maximum effect. Since oxygen is the driver and ultimate limiting factor in a plant’s ability to absorb and use both water and nutrients, aeroponics systems focus on providing unlimited access to air. Plants are grown suspended in air, in the absence of a growth medium so that no portion of the roots are limited in their exposure to air.
In the efforts to maximize a plant’s ability to absorb and use nutrients, researchers have discovered that roots’ ability to absorb both nutrients and oxygen depends on how the nutrients are presented. Essentially, roots are able to take in both oxygen and nutrients most quickly and efficiently when the nutrient solution is delivered in very small droplets. There are several types of typical aeroponics systems, and their primary differentiating factor is the size of droplets they deliver.
Low pressure
Low pressure aeroponics systems are typically configured so that plant roots are suspended either above a reservoir or inside a channel that’s connected to a reservoir. Nutrient solution is sprayed over the roots, which then is free to drip down back into the channel or reservoir, where it can be reused.
Low pressure setups are relatively uncomplicated, inexpensive, and built from widely available components, which make them a popular choice for small-scale hobbyists, but they have some distinct disadvantages. Low pressure pumps don’t have the power required to create very small droplets, and their larger drops aren’t able to completely penetrate a dense root mass. When parts of the root system dries up, those sections aren’t able to absorb adequate nutrients, which limits the plants’ overall growth.
Since it’s harder for roots to absorb the nutrients carried in larger drops of water, and the drops tend to gather and drip off quickly, the nutrient solution must be applied more frequently and in greater amounts. Often, roots don’t have an opportunity to dry off between soakings, leaving them constantly wet. In fact, this kind of low pressure aeroponics (LPA) is often referred to as “soakponics”. It’s pretty apparent that this situation doesn’t allow roots unfettered access to oxygen, so these setups aren’t able to maximize growth as much as other, more expensive systems.
LPA systems still do have their niche, primarily because they are relatively cheap to buy and set up. Inexpensive components like pond pumps are well suited to pushing large volumes of water at low pressure, for example, but since these pumps will typically be in constant use, the energy cost can be comparatively high. Overall, though, LPA systems are easy to maintain, and for all their disadvantages, they are more efficient than other non-aeroponics types of hydroponics. While they’re not suited for large or commercial operations, LPA systems are a good option for hobbyists or demonstration projects.
High pressure
High-pressure aeroponics systems are characterized by the size of droplets they are able to deliver. In these systems, nutrients are delivered in droplets ranging from 20 to 50 microns using a high pressure diaphragm pump and appropriately sized mist heads. Plants do best when droplets are in this range since they absorb the mist more efficiently. This means that there’s no need to provide a constant spray across the roots, as there is in LPA systems. Instead, mist is applied at frequent intervals for short periods of time, often less than 5 seconds. Since the droplets are so readily absorbed, there’s no need to spray the roots constantly and, compared to “soakponics”, HPA plants have much greater access to oxygen over time. In HPA, a typical cycle may be 5 seconds of mist every 5 minutes, which means plants may be fed a few hundred times per day.
HPA systems are more expensive than their low pressure cousins, not only because high pressure pumps and specialized nozzles are more expensive, but because they also usually include components for air and water purification, nutrient sterilization, etc. The system also requires electric valves, accumulator tanks, pressure valves, and other equipment to function seamlessly.
Overall, high pressure aeroponics is a more advanced system, highly efficient and cost-efficient because water use is minimal and roots absorb nutrients as soon as the droplets hit the root surface. Virtually nothing is lost or wasted, allowing plants in HPA systems to grow up to 20% faster than those in other hydroponics systems.
Fogponics (Ultrasonic Fogger Aeroponics)
Fogponics can be compared to HPA on steroids, except not quite. The concept of fogponics starts with providing water in a nutrient solution to the bare roots of plants, but these systems create tiny water molecules no larger than about 5 microns, which have an appearance more like fog than mist. This persistent humid environment is similar to a rainforest, but full of nutrient-rich fog. The tiny droplets persist and float through the air, allowing them to travel freely, completely penetrating the root mass.
One advantage here is that with such miniscule water droplets, very little damage is done to root systems, even if they are young or delicate. With larger droplets, even those in the 50 micron range from HPA, there is still a risk of root damage. On the other hand, since there is very little moisture contained in fog, it’s necessary to maintain foggy conditions at all times. A particular tradeoff here for the optimized growth environment is an increase in maintenance chores, since accumulated salt and scale is more prone to affect ultrasonic foggers.
