Cannabis Ebb and Flow System (aka Flood and Drain)

Cannabis Ebb and Flow System (aka Flood and Drain)

Cannabis Ebb and Flow System is a very popular method among first time hydroponicists.  It uses a submersible pump in a nutrient reservoir to pump nutrients into an upper tray containing the plants.  The pump is switched on several times a day via a basic timer.  The nutrient solution is pumped up to the upper tray and it floods the root system, getting rid of any old air that was in the root-zone.  Once the nutrient solution has reached the maximum level, it starts to drain back into the reservoir via an overflow pipe.  As the nutrient solution drains back down into the reservoir, the root-zone takes in a fresh supply of oxygen rich air and stale air is pushed out.

More oxygen = increased metabolic rate = increased nutrient intake = more growth!Cannabis Ebb and Flow System (aka Flood and Drain)

Cannabis Ebb and Flow System

Clay pebbles are often used in ebb and flow systems.  The tray is filled with pebbles and young plants grown up in rockwool cubes are inserted into the pebbles once roots start showing.  Other gardeners choose to grow their plants in pots filled with coco coir and clay pebbles, or a mixture of small chunks of rockwool and clay pebbles, and sit these pots in the flood tray.  The capillary action of the roots take up the water and nutrients they need.

Active Ebb and Flow is a low maintenance hydroponics solution, which offers growers more control and great results are possible.  Two key factors to get right are the automatic flood times and flood frequency.

Ebb and Flow System (aka Flood and Drain)When working out how long to flood for, remember the extra time it takes for the nutrients to drain back into the reservoir.  Ideally, you won’t want to be using a standard 15 minute segmental timer to control your pump as fifteen minutes (plus drainage time) is too long for the root-zone to be flooded – a negative to basic ebb and flows.  Obviously flood times will vary depending on the size and exact type of system you are using, but as a general rule of thumb, once the nutrients have flooded to their maximum level (delimited by some form of overflow drainage mechanism that will be incorporated into the system) then it’s time to stop pumping.   All good ebb and flow systems will come already supplied with the correct type of pump – one that allows the nutrient solution to drain back through it.

Ebb and Flow / Flood and Drain Hydroponics, Heath Robinson
Heath Robinson Hydroponic flood and drain Grow. Archived from the HG420 forums 2006 the strain is V3 (NLxG13/Widow)

Here is the grow specs taken from the grow thread:
3 x 600w air cooled hoods
the large 6″ Vortex fan is a two speed controled by a timer so it runs on slow speed when the lights are out. the smaller 4″ fan blows through the Cool shades which now vent out into the growroom.
my nutrient concentrations are,

so here is my rule of thumb:

Seedlings 6 CF

Seed plants and veg growth 10 CF

Flower 12 CF

These concentrations are quite a bit lower than most of you run but it works for me!

Harvest 1661g = 58.7 Oz Dry

The required flood frequency will increase as your plants mature and their nutrient requirements increase.  During the early stages, one flood a day might be sufficient.  Whereas, towards the end of flowering period your plants may require four or more floods a day.  Also, consider what medium you are using.  How much does it absorb the nutrient solution?  A restrictive medium like coco coir will need a lot fewer floods than clay pebbles. My personal favourite flood cycle to use with clay pebbles is flood for 15 mins every 3 hours.

More Hydroponic Systems 


  1. hi Harrison,

    I would recommend the blue lab truncheon for measuring CF its not the cheapest meter but it is definitely one of the best and will last you years.
    I dont like to use additives I am the same as you and only use PK13/14 and if you are lucky enough to grow som monster buds you might want to use liquid silicone to help stop bud rot. But it is only needed on very large dense buds.

    The best tips i can give you is to change out the nutrient solution regularly (maximum 2 weeks) but best if you do it weekly. Try keep your nutrient temps below 72f and try keep your CF around 12 and everything should work out perfect.


    1. Thank you Heath, it is truly great to hear from one of the best.
      I have been inconsistent with seeds, I am in a situation currently where I cannot use a cloned branch and must start from a seedling. I am still searching for that ever so strong gene pool strain that I can replicate over and over. Do you have any seed suggestions?


  2. Hello Harrison,

    CF (conductivity factor) is a standardized way of measuring how much nutrients (feed) are in a hydroponic solution. because hydroponic nutrients are salt based it is quite easy to measure how much nutrient is in the hydroponic because solution conductivity rises or falls depending on how much nutrient there is in a solution.

    EC (Electrical Conductivity) is another way of measuring your hydroponic nutrient strength exactly the same factor as CF, you calculate E.C by dividing the CF figure by 10
    an example woud be a cF 20 = E.C. 2

    Here is a link which explains in more detail about mixing hydroponic nutrients
    I hope that helps


    1. Yes thank you, that makes perfect sense. I just need to get a couple measuring tools and it’s good to go! I appreciate the help and the fast response.

      As an add on conversation, do you use any boosters to go along with your base nutrient? So far I use only use Ionic Grow, Ionic Bloom, and PK 13/14 with a lower end ppm concentration. Any suggestions you could pass along?

      Thanks again,

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