The Ebb and Flow System in a Greenhouse
EBB AND FLOW SYSTEM
One of the most modern grow system methods is the ebb and flow, also known as the flood and drain system. This is a system that is suitable for large area irrigation for potted plants with minimal water consumption. As the name suggests, irrigation water comes up the table through the inlet once the pump or solenoid valve is activated (ebb/flood) and subsides once the pump is turned off or the solenoid valve is closed (flow/drain). During the ebb stage, the plants on the table will be able to absorb water and nutrients through bottom-feeding, thereby avoiding spreading water-borne pathogens and fungi through the wetting of the foliage. During the flow stage, the water and nutrients drain back to the reservoir through a separate drainage system.
Pictured above are Ebb & Flow tables 4ft x 24ft ( W x L)
WHY USE EBB AND FLOW SYSTEM?
Water consumption is a major concern of any commercial greenhouse grower. Municipal source water is expensive in the short and long-run and groundwater deep-well sources are unpredictable throughout the seasons. For these reasons, a properly designed and built greenhouse needs to have a rainwater harvesting collection system integrated with the gutters, where fresh water is collected and stored for use.
Greenhouse grow systems need to be designed in a way where the usage and consumption of irrigation water is coupled closely with a recirculation and recovery system. A properly designed greenhouse doesn’t consume more water than needed for plant absorption. A closed loop ebb and flow system achieves optimal water conservation by using and re-using the same source water for irrigation.
Water flooding the table (looks like a glaze layer)
ADVANTAGES OVER DRIP IRRIGATION
Compared to drip irrigation systems, an ebb and flow system doesn’t need as much maintenance or carry risks in emitter flow uniformity. Where a drip irrigation system uses emitters to direct inject water into the rootzone, a clogged emitter could cause problems which will be visible on the foliage. The ebb and flow method floods the table with a layer of water, so each plant receives water uniformly.
Irrigation setup: 32mm main > solenoid valve > 25mm secondary > 20mm inlet
Drainage Setup: 16mm polypipe > 2″ PVC > 6″ PVC back to pond
HOW DOES THE EBB AND FLOW TABLE WORK?
The Ebb and Flow system is a component of a larger water management system. At the start of the system is the watersource, which in this greenhouse is the rainwater collected from the roof gutters. Rainwater is then directed to the pond catchment populated with fish stock. A submersible pump connected to the irrigation controller via a pump start relay pulls water from the pond into a multi-stage filtration system to clean the water from sediments and pathogens and stored in IBC water reservoirs. From this stage, the irrigation controller works together with a booster pump and solenoid valves to push clean water into each specified zone for a specified amount of time. This process can be automatically set via the controller. As the water fills up the tables, the controller’s timer shuts off the solenoid valve and the table water seeps back down into the drain, which is also interconnected with the greenhouse gutter drainage piping, back to the pond.