Friday, 31 August 2012

Experimental Ecobed.

This Ecobed prototype was built in May 2012.  Water is supplied to the soil from a built in water tank.  Soil fertility is maintained by worms breaking down and distributing materials from the worm farm.  Pests such as slugs, snails, birds and flying insects are excluded from the growing area.  
  • The bed is 1500mm long x 900mm wide x 600mm high.
  • There is a 300mm deep water tank in the bottom half of the bed.
  • Water moves up into the soil from the water tank below.
  • The soil is supported by aged pine bark chips submerged in the water.
  • Shadecloth separates the pine bark from the soil.
  • A water filling and distribution system gives rapid top up of the tank
  • A water level indicator shows the water level in the tank at a glance.
  • A worm farm occupies a space at one end of the bed with access for the worms into the plant growing area.
  • A pest exclusion frame with removable panels is mounted on top of the bed to keep birds and flying insects out of the growing area.
  • A band of copper around the beds rim keeps slugs and snails out.
  • A vertical mounted hatch provides easy access to the water filling tube and the worm farm.
Details follow.

The bed is made from 200mm x 75mm Ecowood Planks and sealed with plastic pond liner.  The bottom 300mm of the bed is used as a water tank.  The soil above this tank is supported by filling the tank with well rotted pine bark chips.  On top of the tank is a layer of 75% shadecloth which stops the soil from falling into the water. 
Buried under the pine bark is a loop of 50mm slotted irrigation pipe used for water distribution and storage.  The 2 ends of this pipe are joined by a plastic "T"joiner.  A 40mm rigid PVC tube sits in the 3rd outlet of the "T"joiner and rises vertically up the front wall of the bed to about 70mm above the top.  This filler tube is clamped to the wall using 2 galvanised saddle clamps.
At each corner of the bed is a 1.8m length of 40mm x 40mm painted steel slotted angle.  It's used to hold the layers of planks together and to support the beds pest exclusion frame.

A fibro-cement board is used to create a partitioned area for use as a worm farm.  There is a 70mm layer of soil connecting the growing area of the bed and the worm farm (passing under the partition board).  By this rout the composting worms are given access to a larger habitat extending into the growing area.

The growing area is filled with a loamy well fertilised organic soil mix, and planted out with vegetables (onions in this case because of the time of the year and the bed's position in my crop rotation program).  The worm bed is slowly filled with finely chopped kitchen and garden waste (not onion family, bread, citrus or meat scraps).  I use about 4 cups of the waste mixed with 2 x the volume of shredded newspapers or straw (to maintain a good balance of carbon to nitrogen in the mix) once a week.  After a few weeks of feeding the bed I added 1000 composting worms.  The delay ensured there were enough micro-organisms in the broken down waste to feed the worms adequately.
The worm farm was covered with a layer of shadecloth to help retain moisture and keep unwanted pests out of the worm food, and a painted timber cover to exclude daylight.  The cover includes 2 removable trap doors enabling me to feed the 2 sides of the farm on alternate weeks. 
I believe the size of the worm farm may accommodate a much larger growing area, and if all goes well with this bed, I will build a much larger one to test this theory.
The rigid PVC tube used to fill the tank with water has an easy to read water level indicator made from a length of 6mm timber dowel and a table tennis ball super glued to one end.  The device floats on the water in the tube, indicating the level of water in the tank.  The dowel pokes through a plastic cap which sits on top of the filler tube.  This cap keeps snails and mosquito's out of the water tank.  Painted rings on the dowel indicate when the water tank is full or empty.  I use this to tell me when I need to refill the tank, and to make sure I don't overfill it.  The aim is to run the tank dry so that roots are exposed to air.  Water rises up through the soil again when the tank is filled.
  As an additional pest exclusion system, self adhesive copper tape is attached to the perimeter rim of the bed to stop slugs and snails entering the growing area.
You can just see the overflow pipe protruding through the front wall of the bed (bottom centre of picture).  This is a piece of 13mm flexible plastic tube which extends into the top of the water tank at a height of 300mm from the bottom of the bed.  It is protected from blockage using a small piece of shadecloth tied on the end of the tube inside the tank using a zip tie.  The overflow pipe is an emergency system designed to prevent the bed from flooding in heavy rain, or overfilling by mistake.

The finished bed photo shows the pest exclusion frame.  The removable panels are covered with 21% shade factor VEG NET.  This netting excludes most flying pests including insects and birds, and gives useful protection from the sun and hot winds when growing plants sensitive to these conditions..  It also excludes pollinators, so when pollinators are required, the panels must be removed.  Access to the worm farm and filler tube is gained through a vertically hinged door built into the front panel.