Also known as flood and drain hydroponics, ebb and flow hydroponics is a system in which a tray (or other container) full of marijuana plants is flooded several times per day with nutrient-rich solution. After a brief period to saturate the media, the tray is then drained back into the reservoir allowing the roots to partially dry out. This is repeated 3-4 times per day.
A submersible water pump is placed in a reservoir and attached to a timer with one or more feeder tubes going to your media or media tray. The main tube should be black (to prevent algae growth) polypropylene ½” tubing. Feeder tubes should be the same except in a smaller ¼” size.
Oftentimes an air stone is also added to the reservoir to oxygenate the water. The air stone is connected to an air pump outside the reservoir. The timer will turn the pump on for a specified period of time or until a float valve turns the pump off when the tray is full. The tray (or bucket) also has an overflow tube to prevent overfilling and spillage onto your floor. When the timer turns off gravity causes the water to flow back to the reservoir.
During the ebb and flow technique the media will then begin to dry out as the water evaporates and the weed roots use the solution for growth.
Several hours later the process will be repeated. If done too often, the roots will ‘drown’ or get rot; too infrequently and the roots will get too dry. The reason it is hard to suggest on/off or cycle times is because it depends on your grow room temperature and humidity, the size (gallons per minute) of your pump, the size of the flood tray, the number of plants, the marijuana strain and the stage of growth. You will need to do some experimenting and expect to change your timer settings every few weeks as your cannabis plants grow larger.
You will need to check your reservoir daily for ph and PPM and adjust if necessary. Even if everything checks out fine, it is a good idea to completely change your reservoir solution every seven days or so. Clean the container well if there is any odor, algae or slime.
Some growers use small individual containers filled with Hydroton (clay pellets) and place them in the flood tray. Others fill the tray with Hydroton without containers. This is simpler and cheaper, but individual pots give greater flexibility. Another popular grow media is large rock wool cubes. Seeds or clones can be started directly in them. The system below uses both types of media.
The plus to ebb and flow hydroponics is the hands-off automation once you get your setup dialed in. The downside is this type of flood and drain system uses more water than most other systems. Like all automated systems, you must be prepared in the case of equipment failure. Some indoor marijuana growers keep a spare water pump on hand or run two smaller pumps instead of one larger pump.