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.
Related: Run-To-Waste Technique
Lets dive more deeper…
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.
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.
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.
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.
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.
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.
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