Step 1: Drill holes into the top before cutting the top off to make the subfloor. These holes serve to allow the water to seep up into the soil.
Step 2: Take three 1 gallon containers and cut them in half. This will be your support for the soil and seperate the water and the soil. Place each half of the containers on the bottom with the open part facing up towards you as shown in the picture to the left.
Step 3: Cut holes in the sides or bottom of one of the support containers - this is your "wick". Fill this part with soil before placing in the earthbox with the others.
Step 4: Cut a hole in the subflooring the size of the top of the wick. Afterwards, cut another hole the size of the top of a small plastic water bottle but place this hole in one of the corners. Next cut off the bottoms of two water bottles and place them inside each other to make a "snorkel" of sorts. Place the top of the snorkel in the hole you made for it in the subflooring.
Step 5: Now place the subflooring over the support containers you just made. Make sure that it fits tightly around the edges and that the wick lines up with the hole that you made in the subfloor for it.
Warning: if your subflooring doesn't reach all the way to the edge it might not work well when soil is placed because it will allow the soil to leak into the water and contaminate the water.
Step 6: You can now place the soil in the earthbox. While filling make sure that none of the soil is leaking down below the subflooring. You can also use half soil/potting mix and half manure or other fertilizer. For example using a mixture of potting soil and steer manure mixed 75/25 works well to keep plants nurished for several months.
Step 7: After filling the earth box to the top with your soil mixture it's time to place the cover on. There are a variety of ways to do this, the simplist is to use the plastic from one of the soil mixtures as the top. You can use rocks in each corner to hold the top in place or use the rim from the subflooring to hold the cover in place. The cover serves to keep the rain and weeds out and the moisture in to create the ideal soil for growing food.
Just as Water travels upwards against gravity in a sponge, it will also do the same in soil. This is thesecret to the self watering containers. 
Step 2: Take three 1 gallon containers and cut them in half. This will be your support for the soil and seperate the water and the soil. Place each half of the containers on the bottom with the open part facing up towards you as shown in the picture to the left. 
Step 3: Cut holes in the sides or bottom of one of the support containers - this is your "wick". Fill this part with soil before placing in the earthbox with the others. 
Step 4: Cut a hole in the subflooring the size of the top of the wick. Afterwards, cut another hole the size of the top of a small plastic water bottle but place this hole in one of the corners. Next cut off the bottoms of two water bottles and place them inside each other to make a "snorkel" of sorts. Place the top of the snorkel in the hole you made for it in the subflooring. 
Step 5: Now place the subflooring over the support containers you just made. Make sure that it fits tightly around the edges and that the wick lines up with the hole that you made in the subfloor for it. Warning: if your subflooring doesn't reach all the way to the edge it might not work well when soil is placed because it will allow the soil to leak into the water and contaminate the water. 
Step 6: You can now place the soil in the earthbox. While filling make sure that none of the soil is leaking down below the subflooring. You can also use half soil/potting mix and half manure or other fertilizer. For example using a mixture of potting soil and steer manure mixed 75/25 works well to keep plants nurished for several months. 
Step 7: After filling the earth box to the top with your soil mixture it's time to place the cover on. There are a variety of ways to do this, the simplist is to use the plastic from one of the soil mixtures as the top. You can use rocks in each corner to hold the top in place or use the rim from the subflooring to hold the cover in place. The cover serves to keep the rain and weeds out and the moisture in to create the ideal soil for growing food. 