Ebb and flow is a recirculating hydroponic system. A timer-controlled pump fills a tray or bed with nutrient solution to a set depth, holds it briefly, and then lets it drain back to the reservoir under gravity. As the solution drains, air is drawn into the medium, so roots get both water and oxygen each cycle.
In practice
Plants sit in containers of rockwool, clay pebbles or coco on a flood table. Floods typically last about 10-20 minutes, and the number per day rises from one or two for young plants to several in peak flower, depending on medium and container size. An overflow fitting sets the maximum level and prevents spills if a timer fails. Reservoirs need to be large enough to flood the tray without running dry, and solution is changed regularly because returning runoff carries salts and root exudates.
Don't confuse with
- Drip irrigation: delivers solution to each pot rather than flooding the whole tray.
- Bottom watering: a manual version of the same idea, without recirculation.
A recirculating (closed) system returns drained nutrient solution to the reservoir to be reused, saving water and nutrients but needing more monitoring and sanitation.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.Rockwool is an inert growing medium spun from melted basalt rock into fibres, sold as plugs, cubes and slabs, that holds water and air in fixed proportions.Clay pebbles (LECA) are fired, expanded clay balls used as an inert hydroponic medium that drains freely, holds a little water and anchors roots.Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.Pot size is the volume of medium a plant roots into; bigger pots give bigger plants within reason, but feeding frequency can let small pots punch well above their size.Drip irrigation delivers water or nutrient solution through tubing and emitters directly to each plant's medium, in measured amounts on a timer or controller.Bottom watering lets a pot absorb water or solution from a tray beneath it, so the medium wets from the base upward by capillary action.A reservoir is the tank that holds a system's water or nutrient solution, the place where pH, EC, temperature and oxygen are measured and adjusted.The wet-dry cycle is the alternation between watering a container and letting it dry back, which refreshes oxygen in the root zone between irrigations.
