ebb and flow hydroponics

Ebb And Flow Sub-Irrigation vs Passive Sub-Irrigation

There are a lot of ways to grow plants hydroponically, each one uses specific nutrients. In this article, we will discuss about the sub irrigation advantages and disadvantages and especially comparing between Ebb And Flow Sub-Irrigation vs Passive Sub-Irrigation.

Techniques used in hydroponic gardening and farming:

  • Static solution culture technique
  • Continuous-flow solution culture technique
  • Aeroponics technique
  • Fogponics technique
  • Passive sub-irrigation technique
  • Ebb and flow (flood and drain) sub-irrigation technique
  • Run-to-waste technique
  • Deepwater culture technique 
  • Rotary technique

What Is Passive Sub-Irrigation Technique?

Passive hydroponics, semi-hydroponics, or passive sub-irrigation is a method of growing plants without soil, peat moss, or bark.

Instead, an inert porous medium transports water and fertilizer to the roots by capillary action.

Water and fertilizer are held in a reservoir and conducted to the roots as necessary, reducing labor and providing a constant supply of water to the roots.

In the simplest method, the pot sits in a shallow solution of fertilizer and water or on a capillary mat saturated with nutrient solution.

Since routine maintenance is much simplified, passive hydroponics can reduce the labor required to maintain a large collection of plants.

The Kratky Method is a specialized passive hydroponic technique that involves plants suspended in net pots above non-circulating water and nutrient reservoir.

The various hydroponic media available contain more air space than more traditional potting mixes, delivering increased oxygen to the roots.

Allowing air to reach the roots is particularly important in preventing root rot in epiphytic plants such as orchids and bromeliads, whose roots are exposed to the air in nature.

Passive hydroponics also may add additional ambient humidity through evaporation.

It is important in passive sub-irrigation to wash out the system from time to time to remove the salt accumulation.

Plants that require drying between waterings or a dry dormant period may fail to thrive under the constant moisture of passive hydroponics.

Passive Sub-irrigation and Hydroponic Farming

Plants are developed in a medium known as inert porous that transports fertilizer and water towards the roots of the crop with the help of capillary action.

This is done from an individual container that is necessary, reduces labor, and supplies constant water towards the roots.

To be said in simple terms, a pot is placed inside a liquid of fertilizers combined with water or with the help of a capillary mat which is filled with the nutrient liquid.

The diverse hydroponic media obtainable are coconut husk and expanded clay which contains more airspace than the traditional pots and this brings augmented oxygen towards the plant roots.

This is a very important method in epiphytic crops such as bromeliads and orchids, as they have their roots uncovered to the atmosphere in nature.

The biggest advantage of passive sub-irrigation is that it avoids a lot of root decay in plants and evaporations bring in the additional benefit of humidity.

This will feed your plants automatically using no pumps or timers.

By using a float connected to a reservoir the nutrient solution can be adjusted to maintain an inch or two inches in the growing chamber automatically.  

This is very simple to build your own sub-irrigation system using as many grow containers as you want for a custom system.

The autopot system makes hydroponic growing easy. No pumps or timers needed.


Read: What Are The Techniques of Hydroponics?

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The Disadvantages of Passive Sub-Irrigation Technique

So as we mentioned above passive sub-irrigation is a type of hydroponic growing system where the soil is replaced with water and nutrients suspended in solution.

Plants growing in hydroponic systems either grow with their roots directly in water or, as in the case of passive sub-irrigation, in moisture-retaining materials such as fiberglass, clay pebbles, coconut husk, or perlite.

In passive sub-irrigation, the inert medium acts as a wick to carry water from a reservoir below the planting up to the plant’s roots.

Like conventional hydroponic growing, the water contains all the nutrients the plants need.

Greenhouse Growing

In passive sub-irrigation, plants are grown in porous media that transport water and nutrients to roots.

Water is run past the media through a system of pipes and sits in the bottom of plant-containing trays.

Sub-irrigation systems usually exist in controlled environments, because the rate at which nutrients are mixed into the solution is very important.

Therefore using sub-irrigation systems outdoors is often difficult, so if you do not have a good indoor space for setting up a sub-irrigation system.

Expensive Equipment

Another drawback to passive sub-irrigation is that it requires special equipment, the cost of which can be prohibitive when you are first starting up.

Although costs vary considerably depending on the type of equipment you buy and how large a setup you desire, it is certainly more expensive than simply planting in the ground.

If you already have an indoor hydroponics system, then retrofitting it to become a passive sub-irrigation system may prove less expensive.

This means modifying your system so that, instead of suspending plants in water, they are only periodically exposed to it.

Fertilizer Frequency

A disadvantage of all hydroponics systems, including passive sub-irrigation, compared to traditional growing techniques, is the frequency with which you must supply the plants with nutrients.

Because they do not have access to soil, which contains many of the minerals and nutrients lacking in water-based growing systems, you must supply it to them in the water.

Buying these nutrients is an extra expense over the intermittent fertilization you might give garden plants, though as passive sub-irrigation does recirculate its water, unnecessary loss of nutrients is prevented.

Disease Development

Because passive sub-irrigation waters plants from below, relying on the roots’ capillary action to draw liquid up into the plant, most plants grown in this way are significantly less prone to foliage diseases.

However, when insects or disease problems do take root, it is often more difficult to manage them because you cannot simply apply drenches the way you would in the garden.

Therefore keeping an eye out for disease is very important, and using integrated pest management strategies becomes even more crucial.

Ebb And Flow Sub-Irrigation Technique

ebb and flow hydroponics
(source)

There are five popular methods of hydroponics, all of which have their advantages and disadvantages.

The method you choose should depend upon which characteristics are most important to you; is its ease of set up, lowest maintenance, largest yields, most reliable, or most cost-effective?

These are just some of the deciding factors.

While all five methods will sound similar, each is slightly different. Each method incorporates growing in a nutrient solution without the use of soil.

Each method will also be dependent on water, nutrients, and high oxygen content for the roots.

Ebb and Flow or “flood and drain” is an effective, relatively low-cost, and very versatile hydroponic system, which makes it great for beginners and pros alike.

Systems come in several shapes and sizes and can be used for the early stages of vegetative growth all the way through harvest.

The mechanics are simple: A hydroponic ebb and flow system work by periodically pumping nutrient-rich solution to the plant sites once, or more often, several times a day.

This flooding (the ‘flow’) meets the nutritional needs of your plants by saturating the grow medium with a solution.

After the mediums have been saturated, the pumps are stopped, and the ‘ebb’ process begins.

The ebb is the draining of the solution back to the reservoir.

This period in between the flood cycles creates a well-aerated and moist environment where your roots, and thus your plants, will thrive.

The ebb and flow system cycles are accomplished with just a few simple hydro components including a central reservoir, a flood tray or modules, submersible pump, timer, and sometimes float valves or overflow drains.

In most systems, float valves or overflow drains prevent overfilling, while one or two timers control the intervals at which your nutrient reservoirs flood and drain the solution (typically multiple times throughout the day).

This straightforward setup with a minimal number of components not only simplifies feeding but also creates a highly effective method of nutrient delivery and root aeration.


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How To Use Flood And Drain Hydroponic Systems?

The ebb and flow of the nutrient solution in a flood and drain system is intended to maximize the absorption of hydroponic nutrients and oxygen in the root zone for faster growth and higher yields.

Basically, water and air don’t occupy the same space at the same time in the medium, and because of this, we use the timing of irrigations to find an optimal balance between the air and water content of the medium over time.

Too much irrigation can compromise aeration; too few irrigations, and there will not be enough solution stored in the medium between irrigations to maintain adequate water and nutrient supply.

Whether you’re using a flood table or a modular system, there are 3 main factors that will affect the frequency or number of times per day you need to run the flood and drain cycles – container size, plant size, and water-retention characteristics of the growing medium. 

The first one there is a bit of a no-brainer, and of course, bigger plants consume more nutrient solution so this cycle frequency will need to be ramped up as your plants grow larger.

Adjusting for different grow medium types is more variable because there are countless medium mixing options, but it still follows a basic principle.

Softer mediums like Rockwool will hold more moisture while hard mediums like expanded clay pellets or stone will hold very little.

While we can’t chart every potential combination, the chart below illustrates general flooding schedules throughout the growing cycle for a few of the most common grow medium types.

Is Ebb And Flow Sub-Irrigation Technique Difficult To Use?

This system seems complex to beginners because it involves so many different components.

But they all come together quite easily and can be assembled in very little time.

Once assembled, this system needs little maintenance and produces plants efficiently with very little electricity or water use.

This method allows you to easily alter your garden, adding or removing plants as you wish without affecting any of the surrounding crops.

Like other methods, the basic concept is very simple–plants are placed in a tray, which is periodically filled with nutrient-rich water pumped out of a reservoir below.

The system uses gravity to return the water to the reservoir to be reused.

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