how often to flood

Does anyone have a starting point for how often to flood and drain?
using 4" rockwool cubes, plants are about 3 weeks old. have been flooding once every 24 hours. cubes always seem to have plenty of moisture. the reason i am asking is because i hear other people say they flood 3-4 times
per day? don't won't to overwater but scared i am underwatering and slowing growth.

I assume your in a a flood and drain table correct. You want to flood 3-4 times a day every 6-8 hours.Usually 10-15 minutes works but you have the table with it overflow tubing so when it hit that overflow tube you can know its enough just time it.I also assume 4 inch cubes are buried in hydroton clay pebbles which is good.Good Luck

Phil, If you're using only rockwool (as is done in my op; I use plastic pots stuffed with loose rockwool 'floc'- see my gallery), flooding once a day is plenty. Rockwool holds many times its weight in water.

However, a 4" cube by itself isn't really big enough to contain the rootmass for a plant all the way to harvest. Also, when the plant gets to about wk3 of flowering, it will want about a litre of water per day, about 3-4x as much as a 4" cube will hold.

On the other hand, if you have a 4" cube in a netpot with expanded clay pellets in the bottom of the pot, FF is right, you'll need to flood 3-4x/day. Clay pellets don't hold much water by themselves.

You have too run some tests to see how fast your medium drys out.so you can set the timer to flood and dry then flood and let it dry and flood.Each medium holds moisture at different rates so you have too test them and see how long they stay moist,then you can set the timer to flood them when they dry out. Hope this helps.Peace

Tokecrazy is on it.

Running the system without plants will give you a very good idea of how much water is lost by evaporation alone, establishing a baseline to work from when you get plants in place.

Right on Toke. I was gonna say the same thing! I'm on my second ebb and flow grow in 4x4 plastic pots with a hydro mix. My girls are about 3-4 wks old and I have been watering like every 2-2.5 days. I flood the tray until it starts to drip back to the rez, and turn it off. It seems good right now, but you have to check your girls a couple times a day. They sort of let you know when they need water and food.

CQ

An accurate way to gauge how much water to give is by subtracting the weight of the pot & media/soil alone from the weight of the pot & media/soil immediately after it has been watered (and has drained fully).

Learn to love metric measures. Since water weighs 1 gram per millilitre, you will know that your pot of media/soil which weighs 500g more with water than without has exactly 1/2 litre of water in it.

If you do what Tokecrazy suggests, that is, running a pot of media with no plant in it under your lights and checking the weight of that pot periodically, you will know how much water is lost by evaporation alone.

Ideally, you're looking to have about 1/3-1/4 of the water remaining in the soil/media at the end of 24 hours. The type and consistency of soil mix/media, the surface area of the pot and ambient temp/humidity will all combine to vary the rate of evaporation.

A pot of media may be able to hold 1 litre of water, but if the water weight doesn't reduce to ~250-330g in 24 hours, you need to reduce the amount of water applied. In a flood system, that can be done by shortening the amount of time that the pot is flooded or reducing the flood depth (shorten the overflow tube or raise the plant up on a piece of tile).