Ebb and flow systems are among the most popular hydroponic systems because of their simplicity and low maintenance. The plants grow in a soil-less growing medium that retains moisture and allows the roots to take in oxygen. Because the medium retains moisture, the system is not as vulnerable to equipment failure; the retained moisture sustains the plants for a short time while the equipment is maintained.
Ebb and flow systems can be simple, such as two buckets attached by a hose, or they can involve a complicated setup with computers automatically sampling the nutrients and adjusting the pH and nutrient levels as needed.
How Ebb & Flow Systems Work
Ebb and flow hydroponics systems are sometimes called flood and drain systems because they work by flooding the roots with nutrient solution, then draining the solution away. The plants grow on the top of a closed container or trough, with holes cut to allow the roots to dangle into the container. Nutrient solution is poured or pumped into the container, filling it. The nutrients then drain away into a reservoir until the next flood cycle. The length of the flood and drain cycle depends on the type of growing medium and the plants grown and can be anywhere from 30 minutes to several hours apart.
The main components of the ebb and flow hydroponics system are the nutrient reservoir and the growing bed. The reservoir and growing bed are connected by a hose or flexible tubing that allows the nutrients to flow back and forth.
In a very simple system, the growing container sits elevated on a table or shelf with the nutrient reservoir below. The nutrients are moved into the growing container by raising the nutrient reservoir so that the solution flows into the growing container. In an automated system, the nutrient solution is pumped up into the growing bed.
The Growing Medium
Hydroponics systems are soil-less systems. The growing container is filled with an inert growing medium that supports the root system and retains moisture. The choice of growing medium depends on the plant, type of system used and the ready availability of media.
Sand is a low-cost growing medium that is usually inexpensive. Sand is good for cloning or rooting transplants, but it drains poorly and retains too much water for most crops. Brick shards, sawdust or gravel can be used when readily available, but they are difficult to clean between crops and may change the pH of the nutrient solution.
Vermiculite and perlite retain water well. Their light weight can be a problem and may not support heavy plants.
Rockwool is a manufactured material made from volcanic rock. It is more expensive but retains water well and is often molded into cubes that fit together, making transplanting easier.
The nutrient solution feeds and waters the plants. It contains all of the nutrients that the plants need for healthy growth. The formula is tailored to fit the needs of the plant at every stage of the life cycle. Plants are started on diluted 1/4- or 1/2-strength nutrients. As the plant grows, it moves to full-strength formula and is then changed to a bloom formula to encourage flowering and fruiting. The pH of the nutrient solution needs to be monitored and adjusted every three to five days; it changes as the nutrients are used.
Automation of an ebb and flow hydroponic system does not need to be complicated. For most home use, a timer and a submerged pump are all that is needed. The timer must be capable of turning the pump on several times during the day, filling the growing container with nutrient solution. When the pump goes off, gravity will force the nutrients back into the nutrient container.