How to Flood and Drain Hydroponic Systems

Expert hydroponic watering advice to ensure that you grow the healthiest plants with a flood and drain system.

When it comes to growing the healthiest plants, flood and drain hydroponic systems—also known as ebb and flow systems—are highly flexible, precision-timed watering systems that give you a tremendous amount of control over your hydroponic set-up. A pump is used to flood your plants with a nutrient-rich solution at timed intervals and the solution is then drained into a reservoir, pulling fresh oxygen into your plants’ root zones as it goes.

Flood and Drain Hydroponic System
Flood and Drain Hydroponic System

What are the benefits of the flood and drain system?

There’s no danger of nutrient salts building up in your growing medium because any unused nutrients are drained back into the reservoir. The constant flooding and draining also ensures that your plants’ root zones receive a superb flow of fresh oxygen. This results in happy, healthy plants that grow faster and stronger.

Why is it important to get the timing of your flood and drain system right?

If you flood your plants for too long—or not long enough—you could kill them. So how often should you flood and drain your hydroponic set up? The answer lies in the size of your growing container, the density of your growing medium, the size of your plants, and the heat and humidity of your hydroponic garden.

We promise that this sounds so much more complicated that it actually is! Just think of it this way: larger growing containers take longer to dry out than smaller ones, and a growing medium that is denser takes much longer to dry out than a lighter growing medium. Larger plants can drink a huge amount of water, and heat makes water evaporate quickly.

Hydroponic Clay Pebbles
Hydroponic Clay Pebbles

What growing medium should I use?

This is where things can get a little complicated. Rockwool, clay pebbles, hydroton, coco, etc. They all have different flood and drain requirements, so here’s the low-down to put your mind at ease:

Rockwool: Rockwool holds a lot of water, so it’s worth checking the cubes before you water. If they’re saturated, skip the scheduled watering. Also, rockwool has great wicking capabilities so the solution only has to cover around 30-50 percent of the rockwool. It will automatically suck up the rest of the water itself.

Hydroton: Given that hydroton doesn’t have the wicking ability of rockwool, bring the water level up to the same level as the hydroton, which will ensure that your plants’ roots are saturated.

Clay Pebbles:  Dry clay pebbles release nutrient solution over time, which means you can flood and drain your hydroponic system frequently without worrying too much about the dangers of over-watering.

Coco & Clay Pebbles: If you’re not able to flood and drain your set-up very often, consider a mixture of 20-40 percent coco and 60-80 percent clay pebbles. As coco holds a lot of water, constant flooding and draining isn’t necessary. This will also buy you a little time to respond to any pump failure issues that may arise.

Hydroponic water overflow
Hydroponic water overflow

How often should I flood and drain my hydroponic garden?

When setting up a flood cycle, you need to consider three things: flood frequency, flood height and flood duration.

As mentioned earlier, flood frequency is determined by the growing media. Frequency is also determined by the size of your pants and the climate you’re growing in. If your plants are large or growing in a hot and dry climate, they’re going to need more water.

When you’re trying to determine the correct flood height—how high the water should rise up each pot during flooding—again consider the growing medium you’re using. However, a general rule of thumb is that the maximum flood height should never rise higher than your growing media.

The total time of each flood and drain cycle—the flood duration—depends upon the number of pots in your system and the growing medium being used. Get a stopwatch and see what works for your plants. And don’t hold your flood for longer than ten minutes, as leaving your plants’ roots completely covered for too long can attract disease.

Are there really no rules?

There are no hard and fast rules when it comes to setting up your flow and drain system because every system is different. Instead, it’s about timing the flood and drain cycle, keeping a close eye on your plants, and maintaining precise records of each cycle.

So, what’s the secret of success with flow and drain systems? Getting to know your plants. Familiarize yourself with the weight of a plant when it’s just been watered and the weight of a plant when it’s totally dry. You’ll soon get a good understanding of when your hydroponic garden needs to be flooded.

And don’t be too hard on yourself. Experiment and record your findings, then it won’t be long until you have your flow and drain system working like clockwork—and the healthiest, happiest plants in your hydroponic garden to show for it.

Get the Most Out of Your Hydroponic Plants