Strelitzia reginae

Source: Own work

Strelitzia reginae

There are two groups of techniques for hydroponics:

  • passive technique: the nutrient solution is stationary and the plant takes what it needs
  • active technique: the nutrient solution is rinsed or atomized along the roots

The application of passive or active hydroponics depends on the use: passive techniques are more suitable for growing on a small scale, e.g. house plants in the living room, while the active techniques more suitable for large scale cultivation.

1. Passive techniques:

In the passive or static techniques, the nutrient solution is stagnant and may or may not be oxygenated.

This is also called sub-irrigation or semi-hydroponics.

Deep water culture

Source: Tamaki Sono

Deep water culture

1.1. Stagnant nutrient solution without substrate:

Also called deep water culture. The roots of the plant are directly in the nutrient solution and the plants are installed without any substrate.

This is the most basic technique. The one you would use with cuttings when you place cuttings directly into a jar of water.

The plants can be secured with a ring, by placing them in a hole in a plate or in a floating basket, just above the nutrient solution.

This can be applied for a single plant, or a series of plants.

The container can be anything: a glass jar, bottle, recycled plastic jar, bucket, barrel…

The important thing is that the container does not allow light in, to prevent algae growth. This can be done by taking an opaque container or coat it with aluminum foil, white paint…

The system can be more sophisticated by the addition of an aquarium pump to oxygenate the nutrient solution, which is beneficial to the roots.

For prolonged use, it is important that the nutrient solution is monitored, the concentration of nutrients should not be too high or too low. You check with an electrical conductivity meter and then you can adjust the solution by adding water or nutrients.

It is also possible to throw away the old nutrient solution at regular intervals and a fresh solution.

Avocado in hydroponics

Source: Own work

Avocado in hydroponics

1.2. Stagnant nutrient solution with substrate:

The roots of the plant are in an inert and porous substrate.

The nutrient solution is brought to the roots of the plant by capillarity. The suction power of the roots determines how much the plant absorbs.

In principle, the plants are in a net pot (such as for aquatic plants), and they are above the nutrient solution. The nutrient solution takes up 1/3 of the height of the pot, the plant is in the upper 2/3 of the pot.

This technique is particularly suitable for house plants and office plantings: you can plant 1 plant per pot or have a plant arrangement in a common container without worrying how much water each plant needs as each plant takes what it needs.

1.3. Semi-hydroponics:

Semi-hydroponics is a cross between hydroponics and irrigation system for growing in soil.

The plant itself is in a pot with soil and this pot hangs over a nutrient solution.

The nutrient solution arrives at the roots by capillarity, by means of an inert and porous substrate (usually clay granules), or a ribbon.

This is not “real” hydroponics but it can be a good solution for those who do not have green fingers.

2. Active techniques:

In the active or dynamic techniques, the nutrient solution is brought to the roots or the roots are misted with nutrient solution.

This requires the use of a pump or vaporizer with electric drive.

This technique is more complex than passive hydroponics but it also allows for better control of the nutrient solution as this is stored in a separate container.

For a hobby breeder, active techniques are costly and complex. They are mainly used in horticulture.

2.1. Continuous-flow system:

The nutrient solution flows continuously along the roots, driven by a pump.

The plants themselves can be planted in different ways: in a slab of rock wool, in closed and inclined tubes without substrate…

The advantage is that the plants get an optimal proportion of a water-air-feed.

2.2. Ebb and flow system:

Ebb and flow or flood and drain is a system where the roots of the plants are submerged at regular intervals in the nutrient solution.

After a set time, the excess solution flows back into the reserve by gravity.

In this way, the roots get an optimum proportion of water-air-feed supply.

In addition to a pump, this system also has a timer.

2.3. Run to waste:

The nutrient solution is used only once and then disposed of.

In more complex systems, the nutrient solution is collected in a container where it is filtered and adjusted to be re-used.

Drip system

2.4. Bubbleponics:

Bubbleponics has the same setup as the static deep water system but the nutrient solution is pumped up to the roots to water them from above at regular intervals.

The advantage is that the plant is growing very quickly and does not need to develop roots first to reach the nutrient solution.

2.5. Drip system:

In a drip system, the nutrient solution is brought to the roots with individual drippers at each plant.

The plant itself is in a substrate.

One dripper per plant should be enough but as a precautionary measure, usually 2 or more drippers are placed per plant, in case one of the drippers would be blocked.


2.6. Aeroponics:

The nutrient solution is misted on the roots, continuously or at regular intervals.

There is no substrate, the roots are suspended in a growth chamber.

This system has the advantage that the roots have an excellent aeration.

2.7. Ultraponics:

Ultraponics is one of the most recent techniques. The nutrient solution is vaporized on the roots with an ultrasonic atomizer.

The ultrasonic atomizer is an electrical device with ceramic membranes, which vibrate at a certain frequency. When the water runs over these membranes, it is transformed into a mist of very fine droplets (less than 5 microns). These droplets are so fine that they can be absorbed immediately through the pores of the roots.

This mist circulates in the tubes in which the roots are housed, conveyed by a fan.

This technique is particularly suitable for the horticultural industry.