Hydroponics 101: Ebb and Flow Systems

A super-efficient hydroponics system used widely by indoor growers of all types is the ebb and flow or flood and drain system. This system comprises two essential parts: an elevated flood tray filled with pots and a nutrient solution reservoir. 

At carefully timed intervals, the reservoir floods the tray to provide nutrients to the potted plants. Eventually, the nutrient solution 'ebbs' and drains back into the reservoir placed below. This cycle delivers the ideal amount of hydration and nutrients to the hungry root systems, with virtually no waste.

Ebb and flow systems are simple in concept but somewhat complicated in the technicalities. Ebb and flow are prone to pH drift and nutrient spikes. However, many growers consider it one of the best hydroponics systems (and there are many alternatives!).

The Basics of an Ebb and Flow Systems

What is ebb and flow? It's a hydroponics system for growing plants indoors, without traditional soil. Ebb and flow systems involve a large deep tray regularly 'flooded' with nutrient solution to feed the potted plants placed within it. The nutrient solution runs on a set schedule, usually for five to ten minutes (timing depends on the system's details). Once the timer turns over, the system ebbs back into the reservoir. 

During ebb, the nutrient solution drains from the flood tray to return and recycle within the reservoir. The flood tray usually houses multiple plants and sits well above the reservoir to take advantage of gravity. 

What essential parts make up most ebb and flow systems?

  • Airstone
  • Submersible pump
  • Reservoir
  • Grow Tray
  • Growing medium
  • Digital Timer
  • Inflow and overflow hoses
  • Filters

Hydroponics stores are overflowing (no pun intended) with commercial ebb and flow systems, but you can also easily build a DIY system to suit your specific needs. For example, a robust, opaque Tupperware container with a lid works perfectly as the reservoir. Opaque is vital to reduce problematic algae growth, which is a nuisance in hydroponics.

A large, high walled tray would work as a flood tray, although the ideal options are ebb and flow trays designed with channels to avoid pooling water. The flood tray sits above the reservoir on a sturdy table or shelving unit. The inflow house moves water from the reservoir into the flood tray, scheduled with a digital timer. 

A mechanical timer is not ideal as it doesn't come in small enough increments (typically 15 to 30 minutes). Flood and drain hydroponics usually only need floods of 10 minutes or less, so a digital timer works best.

A secondary hose with an overflow allows the water to drain back into the reservoir when the flood period is complete. Just like with the DWC system, the airstone aerates the water within the reservoir. Although a submersible air pump is preferred for this hydroponic setup, inline can also work.

How to Build a Recirculating Ebb and Flow System

  1. Set up the Reservoir: Choose a tote (that comes with a lid) large enough to hold all water in the system. Connect a submersible pump sitting inside the tank with a digital timer (outside) and the inflow hose, which connects to the flood tray above. Set up the air stone on the floor of the reservoir.
    1. What Size Pump Do You Need? Calculate the square footage of the flood tray, and use the following formula to determine the size of pump you'll need:

(Square Footage x 1.25) x 10 = Pump size

  1. Set up the Flood Tray: Directly above the reservoir, you'll place the garden bed or flood tray. Place the drain hose (with overflow attachment) at the lowest point of the tray. Most commercial options will have this feature pre-cut. This ensures all water drains during the ebb and reduces risks of complete disaster should the timer fail.
  2. Set the Timer for Regular Floods: This may take some tinkering depending on the size of your tray, the number of plants, the growing medium and the stage of growth. Essentially you want to flood with just enough nutrient solution to saturate the growing medium, but without allowing the roots to sit in water. Usually, this is between five to ten minutes for each flood. Do not feed during dark hours.

A few recommendations based on growing medium (but again, test

within your own system):

  1. Clay Pellets: 5 to 10 times a day
  2. Rockwool: 1 to 2 times per day
  3. Coco and Perlite: 1 to 3 times per day
  1. Place the Pots: So long as you plan for the mature canopy space, you can fill a flood and drain system with as many plants as possible (adjusting nutrients to account for more plants). Fabric pots are ideal, as they allow for efficient absorption of nutrients during the flood, but plastic garden pots are also options. 

Ensure the seedlings and clones are well rooted before placing them in an ebb and flow system, or the young roots may not be able to access the nutrients. For young plants, top feed for the first week or so to ensure they are getting the nutrients they require.

  1. Monitor pH and Nutrients: Over time, plants absorb more water than nutrients. This concentrates the nutrient solution, and you'll begin to see severe pH drift. Monitor frequently, and adjust as needed. Top up nutrients and water every few days, and replace it every few weeks.

Step Up Your Indoor Grow With an Ebb and Flow System 

What is ebb and flow if not an indoor version of real-life floodplains out in the wild? It's a regular flood that feeds the root systems of plants before draining back into a larger reservoir. But unlike nature, it's exponentially more controlled and dialled in for bigger, more efficient growth.

While an ebb and flow systems are simple to set up, getting the nutrients and the pH levels right can take a bit of experimenting. Once you've got a handle on the flooding schedule, nutrient absorption, and pH drift, this system requires little upkeep. It's truly a set-it-and-forget it hydroponics system.

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