Drowning plants :(

After I built the "ebb and flow" bucket, I had the timer set to 15m every hour for lighted hours. I am using expanded clay medium. The plant appeared to do ok for day one, but today it is wilting horribly. The one i have hand watering once a day seems to be doing fine. I now have it set for 15m every 3 lighted hours.

Here is my question, how often (ballpark) should I be flooding the bucket?

I think you are letting the roots go too dry for a long period of time in between the floods. The rocks do not hold enough water to sustain the root for that long. If you have a mechanical timer, I would set it 15 on 15 off and see if it recovers. If the water isn't stagnant the plant shouldn't be drowning. I am used to working with coco, so I may be mistaken. Trying to help brainstorm.

You only need to flood long enough to get the clay thoroughly wet. The plants will feed off of the thin layer of water that the clay holds.That thin layer of water is the whole reason for flood/drain. Its NOT the flood that is special about flood/drain - its the drain time that can make it work better than other methods.

Its that thin layer of water that is the key to flood/drain. That thin layer will stay at 100% DO because its so thin. The thin aspect is what lets it reach 100% DO quickly. It takes a long time for O2 to disperse through thick layers of water, but really thin one reach 100% DO very quickly. Very thin. Plus roots just like some air around them - but not too much or too long.

So, its important to think of your plants "drinking" mostly when the water is drained out. Leaving the water sit in a full up table is counter productive in flood/drain. You may as well be doing DWC if you're leaving the roots in water too long. They will do best when they have the minimum amount of water - just enough to keep and refresh that thin layer on the clay.

So, you need to time your floods to the ,minimum needed to wet out the clay. Then time the drain cycles so that the next flood comes before that thin layer of water is all used up by the plants. Clay balls hold water for a long time, but remember the plant is drinking it up as time goes by. You will need longer 'dry' times at night when the plants drink less and shorter 'dry' times during the day when they drink more.

I personally think flooding for more than 5 minutes is keeping your plants from seeing the full benefits they can achieve with flood/drain. The whole time they are flooded they are getting less than ideal O2/water ratios.

You will have to do trial and error as far as the drain or 'dry' times to see what your particular setup and plants like.

oh - if you just transplanted them into the flood/drain from some other setup, they will need a few days to adjust to the changes in root environment.

Yeah what he said

The roots are not drinking the water yet + stress from transplanting = wilting the first few days.
Basically that's why a high humidity is a must - plants drink water through the leaves. If you have it outdoors - cover it by some plastic with few holes. If you have it indoors, buy yourself an ultrasonic humidifier. Or just spray it with some root booster from time to time.

Thanks everyone! I really appreciate the feedback.

I shifted it to a pot filled with mixed Coco/perlite, which is what I use for everything else I grow. I hand water fresh mixed nutes to everything else on the table (raised bed potted veggies) twice daily with the same "soil" mixture and have not had any problems. I was going to set the system up with a 2x3 foot shallow flood table as I have used that sort of setup with good effect on everything I have grown...6" or 8" rockwool blocks for tomatoes and peppers (mmmmm, loooove peppers!) and a few medical plants.

I am going to continue with this thread and rework the system into something I am more familiar with and keep journaling.

Roots can only absorb oxygen when they are wet.

When they are fully submerged in water, you have to make sure that there is plenty of DO in that water. (DWC or waterfalls for example)
Getting maximum DO is very, very easy. Just stirring your water every hour could be enough. Even the Kratky method works, so people make a big fuzz out of it. Often totally unnecessary.

When they are not fully submerged in water the whole time (soil, cocos, rockwool) they will absorb the oxygen in gaseous state. Not directly however. The roots are wet (a thin layer of moist) and the oxygen in gaseous state hits this thin layer of water and turns into Dissolved Oxygen.

With FD you use both technics: When the water floods in, there is plenty of DO available: because of the movement of the water. So it doesn't really matter that much if you flood for 5, 15 or 30 minutes. Plenty of DO all the time.
When the water drains, the roots (and the clayballs in your set up) stay wet for a while and there is plenty of oxygen in gaseous state.
Roots can stay dry for a while; this does not automatically cause problems.
Even if you would have no medium, so just a netpot with a collar, they will grow fine. Also if there is plenty of time in between your cycles.

With hydroton I flooded just long enough to reach full depth every 4 hours and no floods when lights are off.

For oxygen and staying moist that is enough.

Another thing (but I never tried it out myself) is this: Do the roots get enough nutrients when you flood just every 4 hours?
There was a study that indicated that when the frequency of flooding was higher, the plants had a higher weight at the end.

People also make to much fuzz about systems, minutes and what else.
And often they do not understand their own system.
Which leads to giving ridiculously advices that make new growers even more insecure then they already are.
They start thinking that growing is some kind of magic, or that you should be part of a secret society to understand it all.

Plants need CO2, nutrients, water and oxygen basically.
Nutrients.... that can be the hard part.
But the rest is so simple that people cannot believe it is so simple and thus come up with explanations that are overcomplicating it, and just plain wrong.