Aeroponics

Aeroponics is derived from the Greek words for “air” (“aero…”) and “work” (“…ponics”). Although there is a debate of whether it is classified as a type of hydroponics, we think it is. As with the other types of hydroponics, it is a soil-less cultivation technique.

It does not need a growing medium but it needs mechanical moving parts and electricity to function.

Pros (most lead to higher yields)

Cons

Little to no growing medium needed

Requires relatively more expensive components as they need to be pressure-rated (such as powerful pump or air compressor and pressure rated tubes etc)

Uses less water than all the other systems – thus the overall weight is lower and makes Aeroponics perfect fit for indoor gardening

Nozzles need frequent cleaning to avoid clogging

Faster plant growth, better plant health and higher yields due to better root aeration – oxygen in roots is a stimulating growth factor

Maintenance is more complicated due to the criticality of system outages, higher water pressure system, having a timer and solenoid valve and cleaning of nozzles

Harvesting is easier for root vegetables as there is no growing medium

Requires close attention to ensure that roots do not dry up

More energy is available to the useful plant growth as no energy is used by the roots (they do not have to find their way through the growing medium)

The nutrient content of the water solution needs careful adjustments

Health monitoring is easier – roots are easy to access and observe for diseases

 

Harvesting is easier as the plants are in no contact with a growing medium

 

There is no growing medium to be removed and flushed

 

How is it different?

All other hydroponic systems use a growing medium which serves the purpose of supporting the plants and allowing moisture and air to be delivered to the roots.

In aeroponics, there is no physical growing medium (except in the start of the growth cycle to get the seeds started). The plants are supported using holding cups placed in the container’s lid; the container serves the purpose of housing the roots, blocking light reaching the roots, keeping the moisture in and allowing air to surround the roots.

The nutrient solution gets delivered to the roots through high-pressure  (around 60 – 100 psi / 4 – 7 bar) sprinklers/nozzles which create a mist of small droplets (up to 50 microns – to give you a perspective, 40 microns is the threshold of the human eye visibility / 70 microns is the diameter of a human hair).

The mist of droplets needs to successfully reach the roots and keep them well covered. There are though lower pressure systems that work well as long as the roots get fully wet with the nutrient solution.

It is important that the roots do not get dry to avoid plant stress. Thus a timer is needed to operate the booster pump at set intervals. Depending on the growth stage you need to be adjusting the intervals (eg, shorter intervals when plants are larger).

High vs Low Pressure Aeroponics

There are high pressure and low pressure aeroponic systems but let’s start from the principle of operation for each one.

High Pressure Aeroponics

It is a more complicated and expensive system compared with the low-pressure one but it offers higher yields. It requires pressure-rated components that are obviously more expensive.

As previously said, this system requires high water pressure (around 60 – 100 psi / 4 – 7 bar) to allow for tiny droplets to form when the nutrient solution is sprayed out of the nozzles.

There are three containers / tanks in this set up, all three connected with valves:

  • one that houses the plant roots,
  • a second one for the nutrient solution and
  • a third one under pressure – a pressurised tank rather (which has two compartments: one with air and one with the nutrient solution)

The pressurised tank has two compartments separated by an elastic diaphragm or an elastic rubber bladder; one with the nutrient solution and the other with compressed air. You will need an air compressor to pressurize air to the required psi, or you could get a pre-pressurised tank but this will not allow you control the air pressure if for example the pressure relief valve leaks and pressure needs to be topped up.

The high pressure in the nutrient solution part of the system is achieved primarily by the compressed air compartment. The compressed air pushes the elastic diaphragm which then transfers the pressure into the nutrient solution. Now that the nutrient solution is pressurised due to the compressed air, a booster pump ensures that the solution is maintaining the required pressure while the volume of the solution reduces by time as it is used up. The compressed air can expand the elastic diaphragm to a certain degree thus not able to maintain the pressure until the last drop of the nutrient solution. Hence the need for a booster pump.

The release of the nutrient solution through the nozzles is controlled by a powered solenoid valve connected to a timer. The timer is programmed for set intervals (usually a few seconds on and a few minutes off) and sends signal to the solenoid valve to open and close accordingly.

This frequent cycling of 100’s of times every day wears the solenoid valve which would eventually fail and will need replacing. So I would recommend you have a spare one.

The solution that is not absorbed by the plant roots runs off accumulates at the bottom of the root container. The return of it into the pressurised solution system is done by the booster pump which sucks the solution back into the pressurised section of the system.

Now, the pump has two places it can suck the solution from: the nutrient solution tank and the root container when run-off solution has accumulated. The control of the source suction can be done either manually through opening and closing the respective valves (e.g. closing the solution container valve and opening the root container valve when you want to empty the run-off solution) or automatically via a system of motorised valves that would of course require more expensive kit and sensors to be added.

Low Pressure Aeroponics

It is the most common type of aeroponic system due to its simplicity and inexpensiveness (compared with the high pressure systems).

In contrast with the high pressure system the low pressure system does not require a pressure rated nutrient solution container and there is no need for an air compressor as well. The elimination of the air pressurized part reduces the cost and the maintenance too.

The rest of the system is similar to the high pressure system, except only for two things:

  • the choice of the nozzles/sprinklers will need to be made keeping in mind the rated pressure of the booster pump. The higher the pressure it can deliver the more effective mist nozzles are and less effective the sprinklers can get (which form larger heavier droplets)
  • the nutrient solution tank which, under conditions, can be eliminated as the root container itself can have the solution. However as said before, you don’t wat the roots to be covered not even a little by the solution. So the root container either has to be deep or the solution has to be of small volume – and you would have to keep an eye on replenishing more often.

Positioning of nozzles / sprinklers

The positioning of sprinklers or nozzles can be done in 3 ways: spraying upwards , downwards or horizontal.

Setting up the nozzles/sprinklers to spray upwards does not allow the droplets to easily reach the inner and upper parts of the root.

More effective soaking of the root (so that water gets into every part of the root) is achieved when the sprinklers/nozzles are positioned near the top of the roots and directed downwards. This way the droplets or mist reach the inner and upper parts of the root more effectively avoiding root dryness and poor yields.

In both of the vertical set-ups as above, the connecting tubes need to be either under the root container or above. In the first case it may be difficult to access them for maintenance (depending on the container supporting structure etc) and in the second case they will be among the plants and again maintenance will be tricky sometime.

The horizontal set-up will see the connecting tubes placed either inside the root container or outside in its periphery. In the latter, the maintenance/inspection of the tubes is easier.

In all three set-ups though, changing a nozzle/sprinkler will require lifting the root container lid which supports the plants in order to get access.

Typical Problems

Algae, bacteria and other microorganism growth in the solution. Avoid using transparent solution containers where light can pass through. Light encourages microorganisms to grow which can

  • change the chemistry of the solution
  • reduce the efficiency of water injection through the nozzles (less so with sprayers though) that can drop the pressure and the effectiveness of the solution mist/spray to reach the inner parts of the roots causing dryness
  • can cause root rotting, ultimately reducing yield.

Thirst. If you notice that your plants show signs of thirst, then check and try the following:

  • Check if the roots are thoroughly covered with the nutrient solution right after a spraying cycle. If they are not, check if there is an issue with the pressurisation system as below:

For High pressure systems check:

For Low pressure systems check:

1.  is the compressor faulty not providing the required pressure?

2.  is there a leak at the air tubes or joints?

3.  is the booster pump faulty not providing the required pressure?

4.  is there a leak at the water tubes or joints?

5.  Is the diaphragm of the solution container not elastic enough thus not being able to transfer pressure to the solution?

6.  are the nozzles / sprayers too small (check their rated flow rate at the pressure you are using)

7.  are nozzles clogged up and need cleaning or replacement?

8.  is the timer functioning properly or as set-up?

9.  Is the solenoid valve functioning properly?

1.  is the booster pump faulty not providing the required pressure?

2.  is there a leak at the water tubes or joints?

3.  are the nozzles / sprayers too small (check their rated flow rate at the pressure you are using)

4.  are nozzles clogged up and need cleaning or replacement?

5.  is the timer functioning properly or as set-up?

6.  Is the solenoid valve functioning properly?

Overwatering. Although overwatering should not be an issue with aeroponics as any excess water runs off underneath in the root container, it is important to not allow the level of the run-off solution to cover the roots (or parts of them). You need to frequently empty the run-off solution. Roots covered with water for too long means that it is likely the roots are not oxygenated enough.

What you will need

You would need to choose the nozzles to be suitable for producing max 50 microns at 100psi pressure.

  • A root container with a lid on top to hold the plant cups (this container will also serve the purpose of collecting the solution run-off under the roots)
  • A nutrient solution tank (you can eliminate that for the low pressure aeroponics under conditions explained above)
  • A pressurized tank (for the high pressure aeroponics) with pressure relief valve
  • An air compressor (for the high pressure aeroponics if the pressurize tank has a
  • A booster pump
  • A solenoid valve (mains powered)
  • A timer (through which the solenoid valve is powered and controlled)
  • Pressure-rated tubes
  • Nozzles / sprinklers (for high or low pressure respectively)
  • A check valve for the return of the accumulated solution in the root container to the pressurized section of the system
  • Manual valves to isolate sections of the system when required

Please bear in mind that for the high pressure aeroponics you can opt for a simpler set up than what I describe above. Either not have the pressurized tank and rely only on the booster pump or not have the booster pump and rely only on the pressurized tank. These set-ups can work but the complete system gives you better control.

In summary Aeroponics:

  • Simplicity: it is a system that requires mechanical parts and electricity to function. It is more complex than the other hydroponics systems especially the true high pressure one
  • Ideal for: all plants – advantageous for root vegetables as there is no space restriction
  • Not ideal for: low value plants as it is a relatively complicated and expensive system that you want to utilise at its maximum, so you want to be growing high value plants
  • Growth efficiency: great growth rate as roots are very well oxygenated leading to better plant health and higher yields
  • Water efficiency: the best water efficiency out of all hydroponic systems as nutrient solution does not evaporate and is delivered straight to the roots
  • Experience required: you can start by experimenting a bit, but especially with the high pressure system some experience in handling different interconnected systems is required.

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