How a Self Watering Box Works

These boxes are designed to provide a gradient in the concentration of fertilizer and water in the soil. The idea is that the plant roots will go to the area that makes them happy.

The real Earthbox uses two areas (in diagonal corners of the box) where the soil is allowed to go down to the bottom of the water reservoir. These areas provide a wick to allow the water in the reservoir to infiltrate the soil above. It is only necessary that there be good contact between the wicks and the soil so the water has a path to get to the root area.

Soil is placed in the container (even with the sides all around and mounded in the center). You can use "potting mix" but garden variety dirt is cheaper. The only thing I do is take the dirt out of the ground and work it through a sieve I made from some 1X4 wood stock and 1/4" mesh "hardware cloth" (wire screen with 1/4" holes). That step gets the roots and rocks out. (and it allows me to see what an interesting collection of critters are hibernating in the soil)

For tomatoes, you will want to mix a cup of lime into the soil to buffer the Ph.

The next step is to place two cups of fertilizer in the mound in the center and cover it with dirt, so it is surrounded by dirt. This allows the water a path to the fertilizer. I use whatever I happen to have on hand, which is usually whatever is cheapest. I don't think a "timed release" (like Osmocote) fertilizer would be ideal in this application, but I haven't tried it so I don't know . . .

Next, cover the entire soil area with a layer of plastic (Black in colder climates, white in the South). The roots will still get oxygen from the small space between the separator (vinyl shutters in the case of Bob's Box) and the water reservoir.

You will need to make a hole in the plastic to plant your plants in (or seeds).

The "Earthbox" concept is not all that new. I was doing something very similar in the 60's but using a hydroponics solution in the reservoir and sterile growing medium. I got the design from a hydroponics textbook.

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