How Garden Ecobeds Work


Latest update 11th September 2016.

Ecobeds are 600mm high raised garden beds with built-in water tanks.  They are designed to reduce to a minimum the amount of water, fertiliser and pesticide brought into the garden from outside.

Although mine are smaller than I would like at 2.7m long x 1.65mm wide, they are restricted by space limitations in my garden.  The width is fine, its as far as I can reach without climbing all over the bed, but with more space, I would build them longer. Bed length is only limited by the length of lining material available.

Plants grown in an Ecobed are very healthy and productive.  Pests and diseases are controlled using biological means and physical exclusion.  Fertility is ensured by keeping the soil moist and well fed with compost.

An Ecobed's constant soil moisture is maintained whilst still using much less water than conventional beds.  Water travels upwards from the water tank into the soil by capillary action rather like water being soaked up by a paper tissue or a sheet of blotting paper.

Almost all the water consumed is used by plants during growth and transpiration.  None is lost to the subsoil and very little is lost by evaporation especially if plenty of straw mulch is used. 

Generally a full tank of water lasts about a week in hot weather, but an Ecobed full of mature legumes will only last 5 days in extremely hot and dry conditions because they are tall and fast growing and transpiration rates are high.

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 geotextile or shadecloth keeps the soil out of the tank without interfering with the upwards movement of water.

The water tank fills quickly because the slots in the distribution pipe are kept open.  The pipe's corrugated structure 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.

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.  When full, the tank's water maintains a column of moisture 300mm above its surface, and as the water level drops this column reduces in height too.  When the tank is nearly empty the column only reaches 50mm into the soil.

Despite this, well structured active organic soil will still hold moisture in its microbial aggregates above this zone for some time, but once the tank is allowed to drain completely, this moisture is quickly used up by the plants and they dry out and die.

Good organic soil holds moisture right up to the surface when the water tank is full.  If this doesn't happen with your soil, it needs active microbes to maintain the structures which hold water.  You will need to add generous amounts of active homemade compost 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 Rhizosphere 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. 

Ecobeds rely on homemade compost to keep their microfauna healthy and active.  Worms and micro-organisms in the soil are responsible for the ongoing good health and high rates of growth of plants.  I top dress the soil with compost a few weeks before a new crop is planted.  It gives the worm and microbe populations a boost ready for planting the next crop. See (The Soil Foodweb) to understand the interaction between the plants and the soil microbiology.

I keep the soil covered with straw mulch whenever possible to stop the surface from drying out.  This is particularly important when soil is being prepared for a new crop.  It keeps the soil and compost moist and protected from sunlight while the worms and microbes are busiest enriching the soil.

To ensure the Ecobed's worms are fed continuously, I regularly supply chopped kitchen and garden waste mixed with straw to the worm farms.  Its important to keep the worms well fed especially when food in the growing area is scarce just before harvest, they can't easily find food elsewhere, so they must be cared for.

The worm farms are always full of worms, and especially in late autumn when their eggs hatch.  Conditions seem to be ideal for baby worms and they stay there until they are at least half grown before venturing out into the growing area. 

Once a year I clean out the worm farms and replenish them with fresh organic waste.  The worm castings are full of plant ready soluble nutrients and I like to make an aerated compost tea from them to apply to the soil around my fruit trees and shrubs.  Surplus worm castings are added to the compost heap.

Propagating cuttings or seed is easy in my propagator.  A constant supply of moisture and a naturally regulated temperature provide excellent conditions for young plants and I rarely have failures.

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 microbes and keep their numbers and diversity high.  Because my thermal compost is aerated regularly, its beneficial (aerobic) microbes prosper and soil fed with it is generally very healthy.  The soil's microbe balance is shifted towards one where 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.

Vegenet with a 21% shade factor is the netting I use to exclude insects, but I use 50% and 75% shadecloth on my exclusion frames to protect the plants from very hot, dry and windy conditions.  They can be quickly 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 an Ecobed using a perimeter barrier of self adhesive copper strip.  This tape is bonded to the external perimeter of the 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 end plates.

Crops grown in an Ecobed benefit from close attention, but once the fundamentals are attended to they can be quite low maintenance.  The fundamentals include, propagating new plants, supplying water as needed (almost never in cool to mild weather), feeding the soil with compost after every harvest and spraying the plants with 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 once a week.