Going with the Flow: Ebb and Flow Hydroponic Systems

By Jeff Sanders
Published: December 27, 2016 | Last updated: April 27, 2021 12:32:25
Key Takeaways

Ebb and flow, or flood and drain, hydroponic systems are popular with hobby growers because they are easy and inexpensive to build, can be built to fit any space, and provide a happy home for plants to thrive in. Here’s how these systems work, and what you need to build your own.

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Ebb and flow, or flood and drain, hydroponic systems are popular with home growers for many reasons. Besides how easy they are to build, you can use almost any materials you have lying around to build them, so you don’t need to spend much money to grow plants hydroponically.


Also, these systems can be built to fit any available space, both indoors or out, and there is no limit to the different and imaginative ways to design them for that space. Along with being inexpensive and easy to build, plants grow well in flood and drain systems. The flood and drain system works basically like it sounds, by simply flooding the plant’s root system with nutrient solution periodically rather than continuously.

How an Ebb and Flow System Works

The ebb and flow hydroponic system is quite simple. The main part of the system holds the containers the plants are growing in. It can be just one plant, or many plants or containers. A timer turns on the pump and nutrient solution is pumped through tubing from the reservoir up into the main part of the system using a submersible fountain or pond pump. The nutrient solution continues to fill the system until it reaches the height of the pre-set overflow tube so it soaks the plants’ roots. The overflow tube should be set about 2-in. below the top of the growing media.


When the water filling the system reaches the overflow tube height, it drains back down to the reservoir, where it recirculates back through the system again. The overflow tube sets the water level height in the flood and drain system, and ensures the nutrient solution doesn’t spill out the top of the system while the pump is on. When the pump shuts off, the water siphons back down into the reservoir through the pump, draining the system.

Build Your Own Flood and Drain System

To build your own ebb and flow system, you need:

  • Containers for the plants’ roots to grow in
  • A reservoir to hold the nutrient solution
  • A submersible fountain or pond pump
  • A light timer to turn the pump on and off
  • Some tubing to run from the pump in the reservoir to the system to be flooded
  • An overflow tube set to the height you want the water level
  • Growing media of some kind

There are many different ways to build an ebb and flow system good for growing small to medium-sized plants. Large plants simply need larger systems. You can use just about anything to build one, including buckets, tubes, two-liter bottles, storage totes, water bottles, an old ice chest or trash cans. Just about anything that holds water can be used. The imagination doesn’t stop there, either—there are many ways to flood and drain the roots in the system, too.


Make sure there is a way air can get in the top of the overflow without spilling water out. A “T” connector with an extension that is a few inches above the water line will work nicely. This will keep air pockets from forming in the system and make sure it floods and drains properly.

Make sure the overflow tube is bigger than the water inlet tube from the pump. Otherwise, because the water is only going out through gravity, and water is coming in through pressure from the pump, you could wind up pumping in more water than what is going out the overflow. This could lead to water building up and spilling out the top of your system, unless you reduce the pressure from the pump.


Three Main Ebb and Slow Systems

Series of Containers Design – This type of set-up is most commonly used when many different plants in containers are being watered at the same time. It’s important to remember that the system with the plants to be flooded needs to be above the reservoir so the water can flow back into the reservoir by simple gravity, and thus drain the system correctly.

The multiple containers are all connected together through tubing so when the system is flooded, they all flood evenly, and all at the same time. For simplicity, instead of having a separate overflow for each container being flooded, there’s usually only one overflow tube. It connects to the system at the base all the containers are connected to.

When the water height reaches the top of the overflow, it spills over and goes back into the reservoir to be pumped through the system again. The height of this one overflow tube will set the height of the water level in all of the connected containers with the plants in them, as long as it’s level. You can change the water height in all of the connected containers by simply adjusting the height of the single overflow tube.

Flooding Tray Design – The flooding tray set-up is useful when you want to place plants in the system temporarily, need to move them around a lot, or are starting plants to be placed in another, larger system. Instead of flooding separate containers with plants in it, this method only floods one container, usually a shallow square or rectangle container that sits on top of a table. The reservoir usually sits directly underneath.

Water is pumped up from the reservoir into the flooding tray on one side, and the overflow is on the other side of the flooding tray. This ensures water circulates from one side of the tray to the other. Like any flood and drain system, the overflow tube height sets the water height during the flooding cycle and can be adjusted as needed.

Plants are grown in regular plastic pots or baskets, and placed in the flooding tray like regular potted plants. However, unlike regular potted plants, hydroponic growing media is used to pot the plants instead of potting soil. Once the plants get big enough, they can be transferred into a permanent hydroponic system.

One downside to using the flooding table is that algae tends to grow on it, so it should be cleaned out regularly. The top of the tray is usually left open, and light is allowed to get into the nutrient solution in the bottom of the tray, allowing algae to grow. The algae alone isn’t really bad for the plants, but it does use up dissolved oxygen in the water.

Serge Tank Design – The serge tank type of flood and drain set-up is useful when more vertical space is required. With flood and drain systems, the reservoir is typically lower than the hydroponic system so the nutrient solution can drain out of the system via the force of gravity and back into the reservoir through the overflow, and when the pump is off.

But you can still set up a flood and drain system even when the water level in the reservoir is higher than the hydroponic system it’s supposed to flood and drain back from by using a serge tank.

The serge tank system costs more to build because there are many more parts needed. It works on the principle that water seeks its own level. In other words, the water height in one container will be the same in another container when they are connected below the water line. The serge tank serves as a temporary reservoir that controls the water height in all the containers with the plants in them, and is only full during the flooding cycle.

The system operates by pumping nutrient solution from the much-larger main reservoir into the serge tank when the pump timer goes on. As the water level rises in the serge tank, the water level rises evenly in all the connected plant containers at the same time.

When the water level gets high enough, a float valve in the serge tank turns on a pump in the serge tank. The pump in the serge tank then pumps water back into the main reservoir. At this time, both pumps are on—the pump in the main reservoir and the serge tank.

After the timer for the pump in the main reservoir shuts off, the pump in the serge tank is still on. The pump in the serge tank continues pumping all of the water back into the main reservoir, draining the system, until the water level gets low enough. At that point, a second float valve shuts off the pump in the serge tank.

This article was originally published on For more diagrams of these hydro systems, check out this handy resource.


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Written by Jeff Sanders

Profile Picture of Jeff Sanders
Jeff Sanders runs a hydroponics website called to help hydroponics enthusiasts learn how to build their own hydroponic systems, as well as learn about many topics related to hydroponics.

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