Principles of the wicking bed








Wicking beds are well known, the simplest and most common is to have a flower pot standing in saucer of water so the water wicks up into the soil. There are now many variants of this theme but having two separate containers one for the soil and plant roots the other one for the water. There is some wicking connection between the two chambers, sometimes just soil in others with a wicking material such as a cotton wick.

The type of wicking bed I have pioneered has only one chamber and works on the principle of increasing the water holding capacity of the soil.  Now I must declare my interest is in regenerating soil.  Soils around the world are slowly degrading due to a combination of tillage, use of inappropriate chemicals.  The loss of productivity from the poorer soils has been more than offset by the use of fertilisers, irrigation and genetic engineering or breeding of more productive plants.

While there will continue to be improvements in technology there will be some point when the degradation of the soil is so severe that they are no longer effective.  With the global population now at 7 billion people and expecting to increase to 9 billion within twenty years the sustainable production of food presents a major challenge.

Experiments I conducted on soil regeneration in the mid nineteen seventies clearly showed that the key to regenerating soil is to grew something (anything) and keep the soil moist.  If the soil is too wet or too dry the regeneration will stop.

Applying water using the wicking action ensures that the soil is always moist, never to dry or too wet. We now understand that fungi are critical in regenerating soil and they are very sensitive to water level.

The standard single chamber wicking bed is very simple; a water reservoir is maintained below the root zone such that water wicks up to the roots. Many wicking bed users have tried to improve on this simple system by going back to the two chamber system by having one chamber for water (often filled with scoria or rocks) separated from the soil by some form of membrane.

To my mind this just makes the system more complicated with no real benefit.  I have seen wicking beds made by simply digging a hole, throwing in an old tyre, covering with a piece of plastic to form an underground basin, then back filling with the soil.  Any rainfall is caught in the reservoir and wick up to the roots.  The grower just carries on in the normal way virtually forgetting about the underground reservoir.

There are many variations on the basic single chamber theme but it is important to understand the basic principles of how they work which is essentially increasing the water holding capacity of the soil.  Although this is well known this is so important I will review the basic principle.

Soil has two critical water levels. The upper level is the amount of water that the soil can hold without water draining away (e.g. the water is held in the soil by surface tension and known as the field capacity). All the small pores in the soil where surface tension is greatest are full of water while the water in the large pores drains away.

The lower level is set by the ability of the plant to extract water from the soil and is referred to as the wilt point.

The difference between the two is the water holding capacity of the soil.  Obviously these values vary with the soil and plant type but just to illustrate let us take a wilt point of 10% and a field capacity or 20%, this means that the water holding capacity per unit volume of soil is 10%.  For a plant with say a 300 mm root system this is not very much water so frequent watering (assuming water is available) is needed.

The aim is twofold, to increase the available water in the soil and increase the volume of soil that the plant has access to.

There are a number of ways of achieving this. The simple wicking bed has a water proof liner under the soil, which is filled with water and of course the soil or whatever is in the reservoir is now saturated so the soil hold much more water.  Let us for the sake of argument say the saturation level is now 30%.  This has increased the available water from just 10% to (30-10) 20% so nominally doubling the available water.  But also the volume of soil that the plant has access to is substantially increased.

In practise this means that the frequency of irrigation has increased from one of two days up to often seen days, (depending on the plant type).

But the overall aim is to increase the soil quality. This is done by the soil biology, the millions of weird and wonderful creatures that inhabit the soil.  But virtually none of these can photosynthesise (some algae can) so they need a source of energy which comes from plants.  This energy can come from simply adding some organic material (dead plants) to the bed or growing plants to provide the energy.

Some growers do not like the concept of having plastic buried in the soil, largely for environmental reasons. I do not totally agree with this argument but my current research avoids this issue.

I have found that leaves from certain plants contain waxes which will effectively seal the soil and make a waterproof layer for the water reservoir.  The Australian wattle is such a plant however most desert plants have waxy leaves.  My current research focuses on senna alata because it grows so fast and can be grown as an annual or permanent plant.  However I do see the benefit in bio-diversity and use a mixture of plants. For simplicity I refer to these as soil plants – plants grown simply to improve the soil.

There are other ways of increasing the water holding capacity of the soil, particularly the use of laminating where a layer of material with fine pores (e.g. organic material) is placed above a layer with coarser material such that the surface tension pulling he water downwards is removed.  This is a well-established technique used with sand to create a hanging water table. 

However soil is not created by one simple method and needs a system of different organisms.  I therefore inoculate the plants with mycorrhizal fungi. If the soil plants are left in the ground they become a permanent source of fungi which will transfer to the crop plants.

This has certain advantages. Mycorrhizal fungi are much more efficient than roots in extracting moisture so in effect making more water available so lowering the wilt point.

They also transfer water and nutrients from one plant to another.  My soil plants are deep rooted and are generally grown outside the wicking bed, this means they will put roots down deep into the soil and extract moisture and nutrients from deeper in the soil giving a much greater supply of available water.

I also add worm eggs, particularly the amynthus variety which are powerful worms which help aggregate the soil as well as moving the fungal spores throughout the soil.

However perhaps the biggest benefit is the ability to extract nutrients from the soil. We have a very good understanding of the nutrient requirement of plants, but we grow plants to eat and provide us, as animals with nutrients, minerals and trace elements.  It appears that the plant may not need these minerals and trace elements in any quantity - but we do.

Fungi are particularly effective in releasing minerals that may not be accessible to the plants.  They exude enzymes from the tips of their hyphae which can dissolve rocks and minerals.  There seems to be lack of understanding on how these minerals and trace elements affect human health.

I wrote a techno thriller called ‘00 and the soil princess’ (available on my web or kindle) which is pure fancy but  like all fancy has its origins in  facts, in this case a remote village in China.  The people in the village live to great age, in the nineties and hundreds and there appears to be no cases of cancer or diabetes. This has been extensively studied and there is a higher loading of selenium in the local rocks and water.

There proves nothing in the strict scientific sense. We live in an age which is dominated by evidence based science, without this science based evidence our political decision making system does nothing. We seem to have lost the ability to take action based on probabilities.

It is highly likely that our health would be improved with a diet increased in minerals and trace elements.  Science as yet cannot prove this beyond doubt, and it may only be possible to prove scientifically by adopting on a reasonable scale.

Science, quite rightly, has become a corner stone in decision making in our society. The reality is that science does not have answers to many problems and in these cases our political system seems unable to take decisions. In earlier times decisions were taken in a climate of risk, may be not always the right decision but action was taken.

This is certainly the case with climate change, where despite overwhelming evidence showing an almost overwhelming probability that greenhouse gases created by man are causing climate change with its associated extreme weather events a global action continues to elude us.

The third of my books on resolving climate change (available on kindle) is subtitled ‘ how science is failing us’  is not so much about the failure of science but our inability to take decisions where the science is presented as probabilities.

There is overwhelming evidence that soil could absorb some fifty years of manmade emissions.  Enough time to find and commercialise alternative energy sources.  This is a technology hear and now technology e.g. immediately available which at minimal expense could provide protection from climate change and ensure a sustainable food supply for the world. Yet it seems virtually impossible to get these concepts into the decision making processes to avoid climate change which remain bogged in the mire.