What is a flood and drain system?

So what is a flood and drain system?


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It’s one of the most advanced and user friendly media based growing systems available for hydroponics   and is known as the Flood & Drain System. Some folks know this as the Ebb and Flow System. This method of growing is being put into use by an ever growing number of commercial flower producers and can also be used for home growing. The popularity of the Flood and Drain Systems has grown because it provides the optimum in root zone exchange of oxygen, water and nutrients leading to maximum growth and productivity. A Flood and Drain system is suitable for both short and long term crops.


As the name suggests the system has two cycles where it supplies nutrient and oxygen to the roots. The flood and the drain cycles.

FLOOD CYCLE: In order to deliver optimum oxygen to the root system the root zone must be flooded with nutrients. This will push or expel all “dead air” from around the roots.

DRAIN CYCLE: Once the flood cycle has completed ( 2-15 mins) the system has to drain the nutrients quickly in order to pull fresh oxygen into the root zone area as the nutrients drain out. This will leave the roots damp with nutrient and should take between 15 and 45 mins. This is why Flood and Drain is so popular. It’s simple but provides excellent results and is also great for rooting cuttings.


In most cases the Flood and Drain System consists of a lower nutrient reservoir with a pump at its lowest level to deliver the nutrients to the upper level container where the root zone is located. Usually this is filled with expanded clay pellets. There is an overflow pipe in the upper level leading back to the lower reservoir and this is the drain point during the flooding process. This ensures that the upper level root zone container does not overflow.

While the pump is running the nutrient is kept at a pre-defined level in the upper container. Nutrient floods in and occupies all the spaces between the expanded clay and soaks the roots. The nutrients are never standing still during this cycle, because they are flowing up and then back into the lower reservoir through the overflow. The dissolved oxygen levels in the nutrient are quite high because the nutrients cannot stagnate by standing still, and this is vital for the growth of the plants.

When the drain cycle occurs the pump will switch off, and then gravity forces the nutrients back through the pump into the lower reservoir. Usually there is a filter to stop any potential blockage by particles getting into the pump. As gravity begins to drain the nutrient, the spaces between the expanded clay are evacuated, and air rushes into the spaces left by the receding nutrient.

The flooding cycle only needs to be as long as it takes to fill the upper growing container or tray, and the drain cycle should really be at least twice the length of time it takes to flood the container. Usually 15 minutes on and 45 minutes off is adequate. If any root problems appear then lengthen the drain cycle a little more. During the night hours you only require one flood cycle and then another one just before dawn. The number of cycles you require during the day hours will be governed by the amount of water/nutrient your plants will consume at any given stage of growth.



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