How Garden Ecobeds Work

Latest Update 7th October 2017
  • Ecobeds are designed to reduce to a minimum the amount of water, fertiliser and pesticide brought into the garden from outside.  My Ecobeds are fairly compact at 2.7m long x 1.65mm wide, but space is limited in my small suburban backyard, and much longer ones are quite practical given enough space.
Design
  • The schematic above shows how Garden Ecobeds work.  They are lined with a polythene membrane to form a water tank which is full of 20mm drainage Scoria (crushed volcanic rock).  It supports the soil above it and its porosity provides pathways for the water to travel upwards into the soil even when the tank is nearly empty.  A barrier of shadecloth keeps the soil out of the tank without interfering with the upwards movement of water.
  • The tank is supplied with water through a distribution system comprising a vertical filler pipe, a slotted distribution tube and an overflow pipe.  There is a simple water level indicator inside the filler pipe which can be seen easily when walking past the bed.
  • The water tank fills quickly because the slots in the distribution pipe are kept open by the corrugated structure which stops Scoria getting close enough to block the slots.
  • My oldest Ecobed built in May 2012 is still filling as quickly as the latest one built in March 2015 using this design.
  • Although the 250mm deep water tank is full of Scoria, there is sufficient space between these granules and within their structures to contain about 450 litres of water.
  • The tank's water maintains a column of moisture 300mm above its surface, and as the water level drops, the penetration of this column reduces so that when the water tank is nearly empty, the column only penetrates 50mm into the soil.
  • Despite this, well structured organic soil still holds moisture in its aggregates above this column for some time, but once the tank is allowed to drain completely, the moisture is quickly used up by the plants with unfortunate consequences.
  • Good organic soil covered with mulch holds moisture right up to its surface when the water tank is full.  If this doesn't happen, the soil needs active bacteria and fungi to maintain the structures which hold water and nutrients.  However, it doesn't take long for high quality homemade compost to restore the microbiology and rebuild the soil's structure.  I add about 60mm of high quality homemade compost to the soil after it has been cleared every harvest to maintain a high microbial population. 
  • The rise and fall of water in an Ecobed's water tank acts like an air pump drawing fresh air into the tank through the soil as the tank empties, and expels it as the tank is filled.  Plant roots need fresh air to feed the beneficial (aerobic) micro-organisms in the plant's root zone so the air in the soil needs regular replenishment.  Water tanks should be left until nearly empty before refilling, and they should then be filled until they overflow to get the best out of this feature.  
  • Take a look at my blogpage for information about the Soil Foodweb
Fertility
  • Fertility is an issue in an Ecobed because a build up of minerals in its water tank will eventually inhibit plant growth.
  • Chemical fertilisers are highly soluble and drain through the soil into the water tank easily when it rains. This is obviously undesirable so we need to deliver nutrients to plant's roots in a way that doesn't lead to this pollution of the water tank. 
  • The beneficial microbes in biologically active organic soil release nutrients to plants in an organic form as required by the plants in their root zones.  Surplus nutrients, if any, are locked up in soil aggregates formed by bacterial and fungal activity until needed by the plants.
Pest Control
  • Pest and diseases are controlled in Ecobeds using biological and exclusion methods.  I maintain a very high organic content in my soil by incorporating lots of homemade compost to feed the soil's beneficial microbes and keep their numbers and diversity high.  Plant pathogens are out-competed and kept under control.
  • There are beneficial microbes on the foliage of plants too, and to keep airborne pests and diseases under control, their numbers are topped up every month by spraying the foliage with aerated compost tea. 
  • An Ecobed protects plants from flying pests using exclusion netting.  This netting stops all but the smallest insects invading the bed and provides 21% shade from the hot summer sun.
  • Purpose built exclusion frames are designed to make this easy and effective, but I use them sparingly trying to build a balanced community of pollinating and predatory insects and other flying creatures by growing herbs and flowering plants to attract them. 
  • Flying insect pollinators must be allowed access to flowers.   So flowering plants are left uncovered except when conditions demand extra protection from extreme weather. 
  • I use Vegenet with a 21% shade factor on my exclusion frames to keep flying pests off my plants, and I use heavy duty shadecloth to protect my plants from very hot, dry and windy conditions.  It can be fitted quickly over the Vegenet (if fitted), using the frame's comprehensive array of hooking points, when conditions demand and removed when milder weather returns. 
  • Slugs and snails are excluded from Ecobeds using perimeter barriers of self adhesive copper strip.  This tape is bonded to the external perimeter of each bed, and molluscs get a mild shock when they come into contact with it.  It has worked faultlessly for me since 2012, but is becoming quite tarnished on my older beds.  They will lose their effectiveness eventually and need to be replaced. 
  • A family of blackbirds have become a real pest as a result of their foraging expeditions looking for worms.  The worms in my Ecobeds are a particular target and they dig up young seedlings and small plants indiscriminately at the same time.  To protect young seedlings, I cover them with wire mesh tunnels complete with mesh end plates. 
If rainwater supplies fail.
  • Strip your Ecobeds of plants, reapply compost and a thick layer of mulch.
  • A full Ecobed water tank will last this way for many weeks before emptying even in hot weather.
  • This maintains the health of the soil while you are away from home.  You simply plant new crops when you return from your holiday.
  • Similarly, if your rainwater tanks run dry in a drought.  Rather than contaminate the Ecobed with treated water, shut the beds down as above, and restart when rain restores your water tanks.
  • Currently, I use a small household inline water filter to remove chlorine from treated mains water when I run out of tank water.  It seems to work fine and I can fill my 2000 litre rainwater tank overnight.  So far the use of this water does not appear to causing any adverse effects on the Ecobeds' biology, but it costs about AU$90 dollars for every 6500 litres in replacement cartridges.
  • Another option is to aerate a tank load of treated water to drive off the chlorine.  The guys at the Soil Foodweb Inc use this technique on chlorine treated water before using it to make aerated compost tea.  As an additional measure they use 5% homemade humic acid containing active microbes to neutralise other chemicals.
  • I use a bubbler to make aerated compost tea using rainwater.  The process is much the same as the one above, but if I decided to adopt this method to remove chlorine from treated water I would need to scale up my equipment to handle much larger batches (2000 instead of 15 litres).
  • You can see how I aerate 15 litre batches of compost tea on my blogpage at How to build a compost tea brewer.  Obviously a much bigger pump and bubbler would be required, but the basic design should work fine 
Summay
  • Crops grown in an Ecobed benefit from close attention, but once the fundamentals are attended to they can be quite low maintenance.
  • These fundamentals include, propagating new plants, supplying water as needed (almost never in cool to mild weather), feeding the soil with homemade compost after every harvest and spraying the plants with homemade aerated compost tea every month.
  • You can even go away on holiday in cool to mild weather, but if you go for a prolonged holiday in hot weather you will need a friend or family member to water at least once a week.