How to Build a Garden Ecobed

Latest Update 11th August 2016.

This page shows how to build a highly productive organic vegetable growing system which minimises water consumption and uses little more than homemade compost and kitchen scraps to maintain fertility.
The first step is to dig down about 75mm below the surrounding terrain and clear the soil away to a holding area elsewhere in the garden.  A layer of plastic weed-mat is placed over the soil to help keep weeds and invasive roots out of the Ecobed, and a layer of finely crushed rock is applied on top as a foundation for the bed.  The pile of reddish brown crushed volcanic rock (in the photo) is 20mm drainage Scoria and is used in the Ecobed's water tank to support the soil above (see more later).
Nine sleepers each 3m long x 200mm wide x 75mm thick are required to construct the Ecobed's walls . Six of them were cut 2.7m long and 3 of them in the middle to make six 1.5m lengths.

Two of the 2.7m lengths and two of the 1.5m lengths were painted light brown and the rest sandy beige using high quality water based acrylic paint for external use.  Two coats were used to ensure complete coverage.  

Even though the preservatives in the Tanalised Ecowood timber are claimed to be safe for humans, they would not be so kind to beneficial soil microbes, so I'm especially keen to isolate the preservatives from the soil in my Ecobeds.
The light brown sleepers are joined at the corners using 125mm galvanized bugle head wood-screws (2 in each corner).  A sheet of heavy duty shadecloth is stapled to this base layer of sleepers as shown, and turned over so the shadecloth is in contact with the ground.  The short sleepers are screwed inside the long ones to produce an overall dimensions of 2.7m long and 1.65m wide.

Note** The shadecloth is part of the bed's defense against intrusive weeds, roots and sharp objects.
The next level of sleepers is attached to the base layer.  Starting with an end sleeper the timbers are pre-drilled at a 45 degree angle as shown above.  Two 100mm galvanized bullet head nails are driven through the bottom corner of both ends of the sleeper and hammered hard into the base layer until the nail heads became embedded in the timber.
Before fitting the side sleepers in layer 2, a 50mm hole is drilled through one of them 500mm from its end.  This hole is for the overflow pipe through which water is discharged when the tank is full.  

It needs to be positioned 75mm (centre point) above the bottom of the sleeper so that the tank water will overflow when it's 250mm deep.
You can see the overflow hole at the far end of layer 2 in this picture.  Once the end wall sleepers are nailed to the lower level, the sidewall sleepers are screwed into them.  Layer 3 is then fixed in exactly the same way as layer 2.
The 200um builders plastic sheet used to line the Ecobed's water tank is a standard 2m wide, and it is just wide enough to cover the bottom of the tank and 250mm up each side.  Length is not a problem and the end walls can be covered right up to the top.

Two layers of this plastic are used as added protection against leaks, and a curtain of plastic is applied over the side wall timbers where they are still exposed.  This layer is not used to extend the water tank it simply protects the soil from exposure to the timber's preservatives.

The first sheet is cut to length (about 3750mm) and laid loosely in the bed.  One end is pulled up to the top of the end wall and stapled in the centre of the wall.  The other end is attached to the other end wall in the same way.

The sheet is carefully smoothed into all the corners, and the ends stapled all the way across the top of the end walls.  The rest of the sheet is stapled along the side walls and in the corners as shown.  Do not staple the sheet below the overflow level in the bed as this could cause leaks.

The second liner is fitted in the same way.

Once the 2 liners are in place the curtains (2550mm x 500mm) are fitted to cover the exposed timber in the side walls.  They are stapled to the inside of the side walls and allowed to hang.
With all the liners in place, 50mm slotted irrigation tube is cut to length and laid around the inside perimeter at the bottom of the water tank.  This distributes water quickly when the tank is being filled, and adds a little extra water capacity by displacing Scoria.
The filler/overflow components are fitted loosely to the distribution tube to mark the height of the overflow outlet.  The outlet assembly is moved down the filler tube until it lined up with the hole in the bed wall (easily felt through the plastic).
A 38mm hole is drilled in one side of the filler pipe, at the marked position, and the tee connector glued into position using clear silicone sealant.
A second tee connector is glued to the bottom of the 700mm long filler pipe and set at 90 degrees to the overflow tee connector.  The 100mm long overflow pipe is glued into position as shown above.  They are left a couple of days so the silicone can set.
The water level indicator is made from a length of 6mm Tasmanian oak dowel.  At one end of the dowel, a table tennis ball is fixed in place using a blob of silicone sealant.  The silicone is "feathered" around the bottom of the ball and along the dowel to provide a strong bond between the two components.  

When the silicone is completely set, the dowel is cut to its final length of about 600mm.  (75mm of the indicator showing above the filler pipe when the tank's empty).  The device is painted yellow, and the empty position marked in black.  

A plastic cap, with a 7mm hole drilled in the top, guides the indicator as it rises and falls with the tank's water level.  It also keeps unwanted pests out of the water tank.   

Before the water tank is filled with water, the indicator is placed in the filler pipe with the guide cap on.  The dowel is marked as close to the cap as possible with a black permanent marker.  A complete ring is painted around the dowel at this point so it can be viewed from all sides.  This provides an easily seen visual indication of how much water remains in the water tank.
Its most important to make sure the outside edges of the main sheets are kept above the overflow height of the water tank when stapling them in place.
This photo shows drainage Scoria being added to the water tank, and levelled with the water when the tank is full to overflowing.

As you can see the filler system has been installed and fixed to the bed wall using a galvanized saddle clamp and a timber packer.  It secures the system and keep the filler tube vertical.

The hose used to fill the Ecobed's water tank has an in line valve and extension tube.  It allows the water supply to be quickly turned off when the tank overflows and the tube extension reaches past the overflow pipe to avoid water loss during the filling process. 
A layer of heavy duty shadecloth keeps soil out of the water tank.  Note the shadecloth is oversize allowing an overlap of about 100mm all round to secure the edges.
The soil is kept inside the overlap when filling the growing area.
There's no bottom to my worm farm, and the gap below provides plenty of access to the growing areas of the bed.  I use heavily painted untreated plantation pine for the inner end wall of the worm farm.  The inner side wall of the worm farm is unpainted fibro-cement sheet.
The Ecobed is filled with soil to about 100mm from the top, and the water tank filled to overflowing.  After allowing the soil to settle overnight as it absorbed water from the tank, 60mm of homemade compost is added as a top dressing and covered with organic sugar cane mulch.  The bed is left for 4 weeks to encourage its population of worms and soil microbes to multiply as they feed on the compost.

Worms are harvested from garden beds and other worm farms.  They are added to the new bed and supplied with plenty of chopped kitchen and garden scraps buried under a layer of sugar cane mulch in the worm farm.  You may need to supplement this by buying a few composting worms from an on-line supplier.

Birds are always on the lookout for a quick meal of worms, so I use a layer of heavy duty shadecloth fitted over the mulch with a small overlap pushed down the sides to keep it in place and the birds out.
This self adhesive copper tape is an excellent deterrent against slugs and snails, however its important to guard against inadvertently bringing these molluscs into the bed as eggs in compost.  This has only happened to me once since I began using copper tape, but hot compost properly made by the thermal process kills any eggs and I have found no slugs or snails in my Ecobeds since I began using it.
This photo shows the pest exclusion frame partly built.  The bottom rail is screwed into the bed wall along with 6 vertical supports made from 65mm x 19mm x 900mm untreated pine timbers, and 4 similar vertical supports made from 42mm x 19mm x 900mm timbers.  They are spaced evenly along each side.
The reason for using 65mm wide uprights in the centre of the sides frames is to allow me to use 2 short pieces of timber for the top side rails instead of one long one.  My car can easily carry these short lengths from the hardware store, but not the 2780mm pieces otherwise required.

The fixings are 75mm galvanised countersunk wood screws, and the top rails and cross bearers are 42mm x19mm untreated pine.
I use 50mm galvanised countersunk wood-screws for this fixing at the bottom of the 65mm centre verticals.
The other four 65mm vertical supports are mounted in the corners and fixed as shown above.
The top fixing of the corner uprights works well using 75mm galvanised countersunk wood-screws.
Here is a view of the pest exclusion frame in place.  It has been painted in situ using the same type of paint as the sleepers.
The bottom rail is pre-drilled for the 30mm galvanised bullet head nails used as hooking points.
These hooking point nails are hammer in at 150mm spacings (extra ones in the corners) leaving the head and about 7mm of nail exposed.  This position is ideal because the fabric is stretched over the edge of the bottom rail keeping it tightly sealed against pests.  The nails are hammered in at an angle because of the difficulty drilling vertically in this position.  Once they reached the required depth, I bent them until vertical with a few light taps of the hammer.
Here is the completed Ecobed with exclusion netting fitted.  Use a lightweight net (20% shade factor) in pieces 2850mm wide.  It allows a single piece of net to be run from the hooking points on one side of the bed, over the top of the frame to the hooking points on the other side.  To keep this sheet taught longitudinally, fix upward facing hooking points along the tops of both end rails at 150mm spaces.

This leaves the ends of the bed unprotected, so cut a piece of net big enough to cover them allowing an overlap at the top and bottom of about 30mm (beyond the hooking points).  This secured the top and bottom of each end sheet, but leaves the sides of each sheet with a loose overlap.  2 additional hooking points are fixed in the top of the side rails at each corner so the overlap could be anchored securely round the corner.

There are no hooking points mounted horizontally to snag on cloths and bare skin, but care should be taken with the upwardly exposed nail heads partly embedded in the top rails.  These nail heads are rounded and are unlikely to cause any damage, but please take care, if you use this system.
These simple removable hatches mounted on each side of the Ecobed provide good access to the bed for planting, harvesting, soil prep and spraying without removing the net.  They are each mounted using 4 removable Tek screws.   The rather crudely cut holes are in the main net behind the hatch.