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How it works
The
plants are grown in rockwool blocks or small pots filled with Hydroton. A system
like this works best for plants smaller than 24 inches tall. The nutrient
solution is stored in the reservoir and is pumped up to the tray with a
submersible pump through the fill/drain fitting. The pump is controlled with a
timer that turns on a few times per day. Or enough to keep the growing media
moist all the time. The pump only needs to run long enough to reach the top of
the overflow fitting. When the pump turns off the solution flows back down the
fill/drain fitting and out the pump. The amount of solution that goes into the
tray is controlled by the overflow fitting. Ebb and flow is one of the most
reliable and easy to build hydroponic systems.
How to build it
What you need:
Tray
Reservoir
Fill / Drain Overflow fitting Kit
Pump*
Tubing
Timer
* The pump needs to be strong enough to lift the water to the to tray but
not too strong or you will have a fountain! Most pumps have a measurement of how
high they will pump. It is measured in HEAD. If a pump is rated at four feet of
head, that's how high it will pump. Some pumps only have a rating in PSI (Pounds
per Square Inch). To find the HEAD, multiply the PSI by 2.31. In most cases, you
want a pump with a head rating of twice the height that you need to lift the
water.
The
tray must be above the reservoir so when the pump turns off, the water will flow
back down through the pump. You can place the tray directly on top of the
reservoir or make a stand for the tray and put the reservoir underneath.
The
Fill / Drain and Overflow fittings fit in a 1 inch hole. Some of our trays are
drilled and come with the fittings. Install the fittings and connect the pump
with a 1/2 inch I.D. tube. The overflow fitting may need to be extended below
with a piece of 3/4 inch PVC pipe.
The
overflow fitting may need to be adjusted. The tray should only flood to about 80
percent of the height of the growing medium. If you are using rockwool cubes, it
should flood about 2 inches. You may need to add or remove PVC pipe on the top
too. Test this before filling the tray with growing media. I prefer not to use a
screen on overflow fittings. All the leaves that drop collect around the screen
and changes the flood depth. The more debris around the screen, the higher the
water goes. If the water floods too deep, the growing medium will float and your
plants tip over. Or even worse, the tray might overflow!
After the nutrient you may need to adjust the pH. A simple thing to do that doesn't cost a lot and your plants will grow much better! Get a pH test kit and some pH down, just a quart, this is strong stuff and will last a long time. The pH almost always needs to be lowered.
In the photo above I'm using 1.4" rockwool cubes to start some basil seeds in a small tray but you want to use larger blocks, just put the blocks right in the tray.
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