How to Build a Garden Ecobin.

Latest Update 3rd May 2016.

The Ecobin is a self watering garden bed large enough to grow one or two tomato sized plants.  They are made from cheap polypropylene garbage bins, but the water tank and supply system transforms them.

The important things to remember are :-
  1. The maximum depth of the water tank (200mm) is controlled by the position of the overflow pipe.
  2. The water tank will overflow when it is being filled as soon as the water reaches that level.
  3. Even prolonged periods of heavy rain will not flood the Ecobin unless floodwater surrounding it exceeds 200mm.  In this case the bin will drain as soon as the external flooding subsides below the overflow pipe.
  4. The water tank is filled with Scoria to provide support for the soil above it.
  5. The water in the Ecobin's tank will support a 300mm column of moisture in rich organic soil and/or Scoria.
  6. These moist conditions are ideal for healthy plant growth, and because the soil's structures are not flooded, air can still circulate through the soil.  The soil stays aerobic and doesn't smell bad.
  7. The tank water level falls as plants take up the moisture in the soil, and you would expect the soil to dry out above the 300mm of capillary fed moisture.  In fact if you have a healthy organic soil, it will retain some moisture in its structure until it is used up by the plants.
  8. If the tank is left to dry out completely, the plants will continue to use the water retained in the soil structure until it is exhausted.
  9. Eventually the soil biology and the plants will become dehydrated and die.
  10. I refill my Ecobins as soon as the water level indicators says the tanks are empty.
  11. A well maintained Ecobin will grow healthy edible crops, will resist pests and will avoid wilting even in hot and windy conditions.
  12. The cycling of water levels in an Ecobin's tank from empty to full acts like an air pump drawing fresh air into the soil as the tank empties and expelling used air as it fills.
  13. A 50mm layer of fresh straw mulch applied on top of freshly laid compost will substantially reduce water loss through evaporation, and keeps beneficial microbes and worms active in the compost.
  14. The water level indicator gives plenty of warning to refill the tank, but it is not an automatic watering system.
The following illustrated guide shows you how to construct a Garden Ecobin.
Using a 50mm hole cutter, cut a hole in the side of the bin so that the bottom of the hole is 200mm above the bottom of the bin.

Cut a 600mm long filler pipe and a 100mm long overflow pipe from a piece of 40mm (i.d.)  PVC pipe, and loosely assemble the whole system.

There should be two tee connectors, a 40mm filler pipe, a 40mm overflow pipe and a length of 50mm slotted irrigation tube.  Make sure the irrigation tube is long enough to fit snugly in the bottom of the water tank.

Fit the assembly so the overflow tee slides easily through the pre-drilled hole in the Ecobin.

Remove the device and take all the components off the filler tube except the overflow tee.

If you look into the open end of the tee, you will see the filler pipe blocking the opening.   Mark the filler pie in the centre of this opening with a permanent marker.

Remove the tee and drill a 40mm hole in the marked position.  Slide the overflow tee down the pipe until it lines up with the hole (as shown above).
Glue the overflow tee in place with silicone, and once the silicone sets, glue another tee to the bottom of the pipe turned through 90 degrees.

Glue the 100mm long overflow pipe into the open end of the overflow tee.
Use the bottom tee to form a ring with the slotted irrigation tube.  Install the assembly in the Ecobin.

Make the water level indicator by cutting a 600mm long piece of 6mm oak dowel and glue it to a table tennis ball (float) at one end using silicone sealant.

Once the glue is set, spray the indicator with bright yellow enamel paint.  When the paint is dry drop the indicator into the filler pipe, float end first.   Drill a 7mm hole in the centre of one of the blue PVC caps and fit it over the water level indicator.  Fit the cap firmly in place on top of the filler tube.  Paint a 5mm wide black ring around the dowel just above the cap.

When in use, the distance between the cap and the black ring indicates the depth of water in the Ecobin's water tank.  When the ring has dropped level with the plastic cap, its time to refill the tank.
This photo shows the water distribution system in place.  Make sure the bin is watertight at the overflow outlet by sealing the joint with silicone on both sides to avoid water leakage and help hold the water distribution system in position.

Cut the end off the second blue cap to make a sleeve and make a 90mmm disc from a shadecloth offcut.  Cover the end of the overflow pipe with the disc and push the sleeve over it to hold it in place and protect the water tank against invasive insects and small animals.
Fill the bin to the bottom of the overflow pipe with 20mm screenings of Scoria volcanic rock, and fill the water tank with rainwater until it flows out through the overflow pipe.  Adjust the amount of Scoria in the bin so that it is level with the water.

Cut a sheet of geotextile to cover the Scoria, and make a hole so it  fits tightly over the filler tube.  Allow enough extra fabric around the edges so it runs up the bin wall at least 50mm all the way round. 

Fill the bin with good quality garden soil sieved to remove stones and other large pieces of debris.  Make sure you fill the bin carefully at first so no soil gets past the edge of the geotextile.  Leave a 100mm gap above the soil for homemade compost (50mm) and sugar cane straw mulch (50mm).
Apply a ring of self adhesive copper tape around the Ecobin about 280mm from the ground to deter slugs and snails from entering the growing area.  They get a shock when their slime come into contact with the copper and go somewhere else for lunch.  The tape is a bit expensive in Australia, but its worth every penny.  

These bins are growing peas and beans and since its still winter in this photo, the protected sunny position and the heat radiating from the gas water heater has helped them flourish.

I found later when the weather warmed that the moist conditions favoured powdery mildew and I had to move the bins away from the heater.  I used Eco-fungicide to control the mildew.