The basic idea behind a flood and drain garden is to simply flood the roots of your plants for a few moments, and then allow the water to drain away. This flooding takes place once every 3-6 hours, depending on what you are growing and what kind of aggregate (soil alternative) you are using. I have found that my broccoli, tomatoes, and cucumber plants grow best with one feeding every 3 hours, with each feeding lasting 15 minutes. The means to accomplish this flood and drain routine are simple. First you need a reservoir for the water and nutrients to reside in. The reservoir needs to be opaque, so as to not let any light shine on the water. Next, you'll need another container to place the plants in. This container is often referred to as the table. The table will need to be a couple of inches deep, so as to allow the water to rise high enough to come in contact with plenty of the roots. Here are a couple different ideas:
This is a commercial product. The table sits in the top of the reservoir, acting as a lid to slow the water from evaporating. The table being directly above the reservoir allows the water to easily drain back into the reservoir.
This is a half of a 55 gallon barrel that was cut length ways to serve as a reservoir. The table is a plastic storage container that fits snuggly in the barrel and has a 4 inch wall.
These are two bus tubs that I purchased at Sam's Club for $12. By placing a lid on one, and then sitting the other tub on top of the lid, these become an excellent reservoir and table.
Once you have a table and reservoir, you will need to get them setup to be able to flood and drain. A submersible water pump is the easiest way that I have found to flood the table. These water pumps can be found at pet stores near the aquariums or at home improvement stores in the gardening areas for ponds and fountains. A pump that does 150-300 gallons per hour (GPH) will be sufficient for small tables and reservoirs that hold 10 gallons or less. The larger your table and reservoir, the higher output pump you will want. For example if you had a flood table that was 4 feet by 8 feet, you would need a reservoir that holds close to 100 gallons. In order to flood the table to a suitable level in 15-30 minutes, you would want a pump that pushes 800 - 1000 gallons per hour. My favorite way of feeding water from the pump into the table is with these fittings:
Just drill a pair of holes in the bottom of your table for these two fittings (half inch speed bit works perfect). In the picture, to the bottom left, there are the the bottoms of the fittings, which are designed to connect tubing to. Above them to the right are risers that are connected to the bottom fitting to adjust how high you want the water level to be. And to the top left there are small plastic grills that go on top of the risers to keep debris from getting back into the pump or reservoir. I use one fitting with just a grill on it (no risers) and I connect it to the pump. On the other fitting, I put two risers and the grill on it to act as the overflow for the water level, which drains directly back into the reservoir.
In addition to the two fittings, you may want to drill a few small holes (1/8") in the table to allow the water to drain back into the reservoir. Commercial products have all of the holes and fittings done for you already. Here's some pictures to give you an idea:
Notice the holes that are drilled in the floor of the table. I always put a hole in the lowest area of the table, as well as a hole in any area that is sunk in such as the strip to the right. The idea is to ensure that all water will drain out of the table. Stagnant water is a sure way to get algae growing, and you do not want that.
Notice the small black dot to the right of the overflow fitting (top, almost center of the red circle). That is a drain hole with a cover over it to prevent debris from blocking the hole. Also notice how the floor of the table in the commercial product is grooved to direct the flow of draining water to the drain holes. I have not found an everyday item that has a similar floor. I would recommend purchasing a table or "tray" from an indoor gardening store if you want the best solution.
Once the reservoir and table are combined and able to transfer water back and forth with no problems, you are ready to let it go to work for you. An electric plug timer that operates in 15 minute intervals is perfect. Harbor Freight sells them for $6. Set it to have one 15 minute on period every three hours. Add nutrients and plants. If you are using artificial lighting then another timer can be used for 12 hours on and 12 hours off if your plants are flowering. If the plants are growing still, you can leave the lights on 16- 24 hours. Some studies that I have read have shown that 24 hour lighting helps delay the flowering process of some green leafy plants such as basil and cilantro (which you don't want them to flower until you need more seeds anyways).
As far as potting each plant goes, you will want to research which aggregate will work best for what you are growing. There are several options that I am aware of: expanded clay (hydrokorrel), perlite, coconut material, and grodan. I have seen other kinds that are made out of plastic or even glass, but I am not familiar with any of these options except for the expanded clay. It came with the first system that I purchased and works wonderfully for my vegetables. Using the expanded clay is simple: pour about 1/2 inch of it into a pot, place the plant's roots on top of the layer of clay, and then fill the pot to about 3/4 full with the pebbles. One exception is that the expanded clay must be rinsed off before it is used. It is reusable, breathes well, holds moisture fairly well, and is easy to handle. I've had no reason to look for any alternatives.
That pretty much concludes my explanation of getting started with a flood and drain hydroponic garden. Hopefully I have been clear with my explanations.
I will revise this posting within the next few days. Feel free to comment about corrections or any questions that you my have.
Thanks, and happy gardening.
Joe
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