Building a Flood and Drain System
By Kent Elchuck
Setting up the system:
- Cut the two by fours to length so that when the sawhorse legs are set up the reservoir will be slightly lower than the table. Each pair of sawhorse brackets will be joined with another two by four to give the table support.
- Place flood table on the 3/4 inch plywood. For a do-it-yourself flood table, it will be made of 3/4 inch plywood.
Do it yourself flood table:
If wood is used to make a flood table, it should be 3/4″ plywood. Once plywood is cut to size, 1″ by 4″ wood should be nailed to the sides. For simplicity, assume that a 4 foot by 8 foot sheet of plywood is used for the table. Then two eight foot lengths of 1″ by 4″ wood should be nailed to the long lengths of the plywood. One eight foot length of 1″ by 4″ wood cut in half can be used for the short sides. Nail the small sides from the bottom of the plywood. Caulking can be used as a safety measure along the nailed seems.
Put the table on something that supports it. A quick sawhorse can be made with cheap 2″ by 4″ wood and with hinges that the 2″ by 4″ wood slides into. Another two by four (ie. an eight footer for an 8ft x 4ft flood table) is placed between the hinges to complete an instant sawhorse. One end should be an inch or so higher than the other end. In the middle of the two shortest sides two holes should be made about 2 inches from the end of the table using a 1″ hole saw.
Now, two layers of 6 mil black poly plastic should be used to cover the bottom and sides of the table. The spots where the holes should be made will be obvious if the table is store-bought.
Put a thru-hull fitting into each hole. Extra care is needed in the home-made flood table because the plastic should be carefully drawn through the thru-hull fittings and the hole in the plywood by making a small hole in the 6 mil plastic. When the thru-hull fitting goes through the table, black 6 mil plastic should be seen tightly secured against the threads of the thru-hull fitting. Now the plastic can be cut out from underneath the table and the female fastener can be used to tighten the thru-hull fitting to the flood table. The system will now be leak-free. Be careful not to cut into the top layer of plastic. If the top plastic layer has a hole, water can leak into the bottom plastic layer. This will create a balloon-like effect from the trapped water. Cutting plastic away from the thru-hull fitting can prevent water from trapping between the plastic layers.
- Put the pump in the bottom of the reservoir and secure a 1/2 inch female fitting to the pump.
- Now, connect two, four inch pieces of 1/2 inch tubing to the thru hull fittings [for holes that are made at the ends of the tables]. Heating the 1/2 inch tubing with hot water will make the connection easier. Next, connect two 1/2 inch elbows to the 1/2 inch tubing and then connect 1/2 inch black poly tubing to each end of the elbows. When the two ends of the black poly tubing meet in the middle, put in a t-fitting. This can be ran to the pump (with 1/2 inch female fitting).
- Connect the pump to 1/2 inch tubing. Just above the pump, a piece of the 1/2 inch tubing should be cut out and a 1/2 inch T should be inserted. The exposed end of the T should be connected to 1/2 inch tubing and then to a on/off tap that will act as a bypass valve. Another piece of 1/2 inch black poly tubing can be connected to the end of the tap, followed by an elbow so that solution splashes and aerates the solution, without making any mess. 6) Plants can go into a medium of choice.
1-4 gallon containers (mesh pots) can be placed on the table and be filled with soilless mix (i.e Sunshine #2 mix). The plants should at first be top-fed continually (for fastest growth) or periodically (slower growth with a lot less maintenance) until the roots are visible at the bottom of the container.
When the roots are visible at the bottoms of the containers, you should;
- put a 1″ inch layer of perlite on the table. Now, you can feed once a day or as often as you would like. Under identical growing conditions, yields were almost identical from one batch that was fed continually and the other batch that was fed in the morning. Perlite holds air and moisture in between feedings.
- put a sheet of reflective material on top of the flood table with holes cut to size to fit the containers. Reflective will help keep the roots cooler. The reflective can be used with or without perlite underneath. But, if there is no perlite, you will need to feed a few times a day. If perlite is used, one feeding a day is all that is required.
- Now, we bottom feed with flooding and draining. The pump should operate long enough to cover bottom roots (ie. 1/4″ – 3 inches). The reservoir should not be allowed to run dry and the tank should not hold more solution than the table can handle, just in case. But, if you want to make a huge reservoir to cut down on maintenance, an over flow valve can be made and inserted into the flood table. If perlite is used on the table, water level can rise higher per reservoir amount than if no medium is used. A medium can also hold air and moisture in between irrigation cycles. Pump can be set on a timer to run once a day or several times per day.
Place a clone from a rockwool cube into a 1 foot rockwool slab. You will need to do the first couple of feedings from the top until the roots reach the bottom of the slab, or you can allow the table to flood lots of solution for the first couple of feedings. When the roots reach the bottoms of the 1 foot slabs, cut a custom sheet of reflectics material that will cover the table and fit securely over each slab.
Flooding and draining should be done several times a days at a water level over 1/4″. A timer is used to control the period for which the flooding takes place. The time depends on the flow rate and and size of the table. Using a wrist watch and a couple of manual floods will give you the amount of seconds that are needed to be programmed into the timer so that the solution fills the table to the desired level.
What to do with the flood and drain system?
Okay, building the system was the easy part. Anybody can build a system that can give faster and higher yielding results but you must run it efficiently in order to make it benefit you. This means that you need to have two other factors working as well; a proper climate and proper feeding. We are going to discuss proper feeding next.
FEEDING Water Quality
Good feeding starts with clean water and a good fertilizer.
You may have have good water running out of the tap. You can check the dissolved solids content of your water by dipping your ppm meter into the water supply. Hopefully, it does not register more than 0. However, even if it does not register more than 0, you may have more chlorine than you want. Using a good water filter that removes chlorine is recommended for you folk that use town water. For someone in the boonies who uses acid-rain free rainwater/groundwater that is purer than Snow White, you can probably get away with the natural stuff, a cheap sediment filter, or a 1-2 ml of 35% hydrogen peroxide /gallon.
For those of you with the polluted stuff, you can use a reverse osmosis machine that remove about 90-99.X% of dissolved solids from the water. Reverse osmosis machines cost a few bucks, especially those that handle large amounts of water.
Now that you have clean water, you need to give your plants a diet that is not deficient in the nutrients they need. The key to understanding plants is that they start off using only a little water and hardly any nutrient. As plants age, they take in more water and more nutrients/per water. For example, a 20 gallon reservoir may require little maintenance for newly-cut clones in vegetative growth. But, six-week-old plants that are about half way through flowering may mean you are topping up a small reservoir daily. Larger reservoirs will have less fluctuations in ph and ppm. 12 gallons of solution for every 12 square feet will require daily maintenance during bloom. A 40 gallon reservoir can allow you a few days of rest between top-ups/flushing during bloom. To keep costs down and quality up, you may want to feed for three days, then, flush for 1-2 days with plain water (or a diluted solution such as 400ppm). Since you may flush every three days, having a reservoir that needs no adjusting before flushing means you have more time on your hands to do other things. Using two reservoirs (the feeding and flushing reservoir) that can be changed from a connection running from the flood table is the easiest way to feed and do flushings.
If you want to make a reservoir bigger;
- Use a 1″ holesaw and cut a hole in the existing reservoir about 2″ from the bottom.
- Do the same thing with another empty reservoir.
- Insert 3/4″ thru-hull fittings into each reservoir. Make sure that the washers (or o-rings are on the inside of the reservoirs).
- Connect the two reservoirs with 1/2″ poly tubing (or 3/4″ flex hose) and c-clamps.
The easiest way to feed is to buy a formula that will give you what you need. Not all fertilizers are created equal. Some fertilzers have a better supply of nutrients and are ph buffered to work in various water supplies. Most hydroponic formulas are purchased in 1-3 parts. When mixing your own powder fertilizers, you will save lots of money.
Some fertilizers have good ph buffering capabilities. In many cases, you can add the product as per the instructions, then, change the reservoir every few days and add a new batch of plant food. This is not the most cost-effective option, but it is the most brainless choice.
For most all other fertilizers that are not ph buffered, the instructions go like this;
- mix a formula up to get the desired ppm (i.e. 800-1500 ppm)
- ph the solution to desired level such as 6.2-6.7 during veg, or 5.5-6.2 during flowering.
- The ppm and ph should be checked and adjusted daily until you get it dialed as to how the fertilizer will react to the plants during all stages of growth. After a few cycles, your feeding techniques will become second nature.
The hardest and cheapest way to do this is to make your own fertilizer with basic salts such as Calcium Nitrate, Magnesium Sulphate, Potassium Sulphate, Potassium Phosphate, and Chelated Trace Elements.
My book, The Innovative Gardener’s Guide provides some sample formulas for making your own fertilizer, tips for cleaning and calibrating your ph pen and ppm meter, and lots more.