feature common to many systems is that plants are fed from above the roots
(i.e. referred to as “top-feed”). In flood & drain systems however, the
nutrient is fed from beneath (Fig 1.2). This process floods the root zone
to a pre-determined maximum level after which all the nutrient is allowed
to drain back into the reservoir. This process is controlled by a pump,
timer and a specialized ‘inlet’ and ‘overflow’ device:
- ‘Inlet’: This also
serves as the drain outlet. It is positioned as close as possible to the
base of the flood & drain tray. Once pumping stops, the nutrient is able
to fully drain into the reservoir via the inlet and pump. To allow reverse
flow the pump must be of a ‘centrifugal’ type. Complete drainage is
necessary to prevent water-logging.
- ‘Overflow’: This is
positioned at the maximum desired flood height. This means pumping can
only flood to the height of the overflow. To maximize feeding and flushing
of the root zone this valve should be set as high as possible. However, if
a medium is used, avoid wetting its top surface otherwise excessive
disease, pest and algal problems can occur.
Suitable media for flood & drain include
expanded clay, perlite or even none at all. The water holding capacity of
the medium determines the feeding frequency.
Advantages to Flood & Drain
- The flooding action helps prevent
salt build-up in the root zone and achieves uniform root zone pH and
- Flooding purges stale (oxygen
deficient) air from the root zone. Drainage draws fresh air back into the
- Flooding can enhance the penetration
of disinfectants throughout the root zone.
Disadvantages to Flood & Drain systems
- If no medium is used, pump failure
can result in plant death within a few hours, especially in hot weather.