ebb & flow question...flood frequency

I have designed an ebb and flow system using 8" slab trays fitted with covers with 4, 5" holes in each cover (American Agritech products) .

I intend to use 5" mesh pots for maximum root aeration. The covers will prevent any light from reaching the roots.

I will either use rockwool cubes or expanded clay pellets in the pots.

The system will be a sort of "hybrid" (used wrecklessly here) between an NFT and "classic" ebb and flow. American hydro calls this a "net well insert" for their 3' x 3' flood tray.


My question is more general in nature:

How frequent and for how long should the flood cycles be? Or what do I look for in order to quickly adjust the cycles/time appropriately?

Thanks for inputs as always.

i flood my table every 2 hours for 15 minuets when the light is on and one time when the light is off. example, flood your table when the light comes on and then 2 hours after that for 15 minuets until the light goes off. hope this helps as i am still learning too. there is a lot of helpful people here as well as info goodluck with your grow h2ofarmer
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How often to flood (flood frequency) is determined by three factors.
1.How long it takes for the plants to show drooping or wilting between floods.
2.How large the planter of rocks is (wether or not the roots are drying out too much).
3.The dryness of the root mat in the tray outside of the planters must also be considered, you cannot allow it to get too dried out between floods.

A good rule of thumb, with expanded clay in planters is to begin with floods every four hours while the lights are on and watch the plants for any signs of wilting just before the next flood. If 4 hours between floods causes the plants to droop, than shorten the time between floods by a half hour to 3-1/2.

As the plants grow larger, a mat of roots will grow out of the planters, onto the tray between the planters. The floods should be often enough to keep this root mat from becoming too dried out between floods, including the long dry spell overnight during the 12/12 flowering stage. You should monitor the condition of the root mat to make sure the roots stay semi-moist.

A good way to check this is to have the first flood start a few minutes after the lights come on, if the roots are dry before the first flood, you will need to have one fast flood at night. Otherwise the drying can cause stunted growth and reduced yield.

Keeping the tray covered with plastic wrap will help keep the root mat moist and help to slow down evaporation, thus preventing the need for a night flood and helping to keep the rooms relative humidity controlled.

A better solution is to build a cover plate for the tray which holds the planters slightly suspended above the tray to encourage a thick and healthy root mat growing in the tray, which will also cure the problem of roots getting too dry overnight. click here for more details

Remember to check the trays drains often to make sure they're not getting clogged by roots or loose medium (small grow rocks).

Flood duration should never exceed thirty minutes total, from the start of the flood until the tray has drained back to the reservoir. Often times, the companies that manufacture ready made systems like hydrofarm, furnish those half hour increment "pull up" tripper type timers, simply because they're the cheapest item to furnish and not necessarily because they are the right thing for the best results with ebb & flow.

It is best to purchase an inexpensive digital timer to handle the floods, since they allow you to program better flood times. The optimum flood is just long enough to allow the flood to reach the correct flood depth, plus a few minutes to allow the nutrients to wash thru the planters, carrying away accumulated salts from the planters. Try to have the total time not exceed twenty minutes if possible, and never allow it to exceed thirty minutes total time.

With the megagarden for example: The system reaches desired flood depth in less than four minutes and drains away in about five minutes, so a ten minute flood allows pleanty of time and finishes the task in roughly fifteen minutes total.

thanks for the help.

Yes I do intend to have covers over 8" wide flood trays with 5" net pots.

Do you have experience/knowledge of the best medium to use in the pots between small rockwool cubes or expanded clay pellets?

I'm hoping to veg clones in 2 -3 " rockwool cubes and then transfer the cube into the 5" net pots and fill around the cubes with small rockwool cubes or the pellets.

It's probably a trivial question, but I was wondering what would be best to use in the net pots for the flowering period.

appreciate the input.

The clay pellets in my book are the best .Ive seen the lava rocks use with the clay pellets.I like the clay better.I heard to many bad things about rock wool PELLETS causing root rot. Peace

Yeah, large particle agregate is the way to go with ebb and flo.

Wow great info guys, I just wanted to comment for once, I'm not lurkin' just no camera to show off what I'm learning thanks for asking that question

Hello ,I am new to this ,I am running a ebb flood and drain ,I changed my lights from conventional reflectors to a 36" cool tube that houses 2 400w mh bulbs ,my problem doesn't seem to bothering all plants but more than half seem to not be holding up the leaves quite as well as the others.Ph 5.80,temperature of room stays around 68-70 and water is around 68-70,TDS 1000,using ro water on a well ,the system floods for 2 minutes and takes another 1.50-2 minutes to completely drain.Floods about every4 hrs.Plants are about 2-3 wks old,lights stay on 24/7,room size is 5'10"long,4'8" tall and 3'10"deep not a lot of room down there.Can anybody help me.Also now the plants seem to be leaning towards the light did not do that before the light swap was that a bad move on my part?I change my water out every 10 days I use dynagro gro for veggie ,protech sislicone for roots,ph up and down.Forgot to add that downstairs concrete leaks and holds a little water on floor ,will this attribute to anything bad?Plants started in 1.5" rockwool cubes wrapped in insul.

My contribution is that Coco Coir has been working wonders. I germinated in those little expandable peat discs then when they were ready for the hydro system I just placed the whole thing in the 3" net pot with coco surrounding them completely. I only had to rinse the small particles of coco fiber that came through the net in some clean water before setting them in their holes. The roots stay moist on 3 floods a day (4 hrs then 5 hrs between.

My question is for what reason is it suggested that the flood is no longer than 30 Min? how about 45 or 60? i know that the roots can sit in water for too long but the aeration of the solution seems in my head to be substantially increased when it is allowed to waterfall back into the reservoir for longer. I haven't tested the DO or anything but could i get some feed back? I feel as if the less time the water is sitting still the better it is for sanitary reasons

Well...there are a lot of interesting insights here....


Here is an article with a flood calculator that I have used from the get go and it works perfectly. But you are going to have to read and do some testing to get it right.

Flood calc and related article here

Use it....but read every step (and the fine print). I have found no greater tool for flooding. Everything else is guessing.

Good luck