Ebb and Flow

in Hydroponics Mon Nov 25, 2013 2:04 am
by ozzydiodude • The Weird One | 2.084 Posts | 10103 Points

Ebb and Flow is a form of hydroponics that is known for its simplicity, reliability of operation and low initial investment cost. Pots/containers or even the flood tray are filled with an inert medium which does not function like soil or contribute nutrition to the plants but which anchors the roots and functions as a temporary reserve of water and solvent mineral nutrients. Mediums include ( rockwool,hydroton,stg,coco and coco chips,perlite,lava rock)The hydroponic solution alternately floods the system and is allowed to ebb away.

Under this system, beside or behind it is a water/light tight reservoir containing either clean water (un nuted) or nuted water that is is periodically flooded for a short period (5 to 15minutes) then the nutrient solution pumped back into the reservoir. By placing the reservoir below the growing bed, the nutrient solution can drain back by gravity. Root disease occurrence and nutrient element insufficiencies can occur with repeated use of the nutrient solution. Because it is a "closed” system, the re-circulated nutrient solution will require reconstitution, filtering, and sterilization. Within the growing period, the nutrient solution may require replacement, within 5-14 days. The rooting medium will require washing to remove root debris and accumulated precipitates as well as sterilization before reuse.

Principles of operation
The fundamental principle of hydroponics relies on fertilized and aerated water which provides both nutrition and oxygen to a plant's root zone. It often involves relatively sophisticated mechanization processes which can be daunting to casual hobbyists. Nutrient solutions must usually be below the temperature at which pathogen growth can begin, yet not so cool that root activity is suppressed. Active aeration of the fertilizer solution is common, since root systems themselves remove oxygen, creating conditions which also can promote pathogenic bacteria and water-borne molds.

E&F utilizes the fact that the solution is not left in constant contact with the roots of plants, to avoid the need for oxygenating or chilling of the solution. Instead it relies on characteristics of root function to provide passive oxygenation at a high level which tends to suppress pathogen growth.(not always true. This would be pending on current growing enviro and set up.)

Simplicity is maintained through usage of a single, two-directional path for the solution. Water flows in and out using the same tube. When the pump has raised water into the tray, briefly submerging the roots, the pump is rendered inactive using a switch, typically a timer, and the water flows back down the same tube. This eliminates the need for more than one sealed fitting and reduces overall complexity of the system.
Another route to this "path" would be an overflow. Either a hole n tube in the bottom, which is cut to height of max water level then it connects back into the reservoir allowing a continuous flood cycle. Another method is roughly the same but the overflow goes on the side to max water level.

Ebb and flow systems come on according to the water-holding capacity of the medium in which the roots sit, how big the plants are to container size. Highly water-retentive media can require watering only once a day, while others require two to as many as six floodings, with each "flood" stage only lasting a few minutes. The time it takes to flood the roots is not a critical parameter, which means that pumps are often moderate in capacity and can be small for systems sustaining indoor plants. This makes the method popular with amateur and urban gardeners. Gravity acts as drain pump, and aeration is accomplished through thin-filming and positive displacement of air as it is forced out of the root zone by water.

Aeration in ebb and flow systems
Aeration of an ebb and flow system is an important aspect of its operation. Automatic displacement eliminates air which has been de-oxygenated by the roots as the water rises to its highest flood stage. When the pump turns off, gravity pulls the water downwards, which re-exposes the space around the roots to the air.

The film of water left around the roots during ebb has a high surface-to-mass ratio, which means that even as the roots absorb oxygen, its high surface area facilitates re-oxygenation, which can sustain the roots as long as their surfaces remain damp. The high oxygen content of water filmed in this way suppresses most harmful lifeforms, keeping the root zones disease free. In other types of hydroponics this function must be performed by cooling the solution to protect it from pythium, a form of water mold responsible for a condition called 'root rot', in which the outer cells of the roots die, turn brown and slough off when handled. But this is also not just applicable to other systems, you may need to cool your reservoir to keep temperatures down to eliminate water born diseases. This concern becomes greater in small closed off areas where the reservoir is in the same room. Need for supplementary oxygenation using air pumps is also eliminated, which increases reliability and reduces complexity.

Ebb and flow hydroponic systems are also quiet, while using less power than other hydroponic systems, which means that they can be used in environments where acoustic signature and excessive plumbing is objectionable, such as residential or classroom applications where space is at a premium.

There are many pros and cons with this system sad there are with others.
And you are the one that has to weigh out his/her odds and per plan and figure out what will work best for you AND your plants given your circumstances.

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