Stones, sand, organics


I receive many questions from wicking bed users about using stones or sand instead of organic material for the water reservoir layer and apparently this is being promoted on some user’s web sites.


First let us discuss stones. Wicking action depends on a small pore size so stones have very little wicking action.  It is true that some plants will put out roots, even through the air, in search of water so stones may work sometimes, but generally they are not good at lifting water.


Another problem is that soil will tend to infiltrate into the gaps between the stones making a sort of concrete which is very hard to work.


Sand is a much better wicking material and some sands with a mixed particle size are very effective at wicking but will still suffer from infiltration of fines.


To avoid this some people put a layer of cloth, such as geo-textile of shade cloth to prevent the soil falling into the gaps.  This again reduces the wicking action and adds considerable cost.


Organic material on the other hand has many advantages. The pore size within the organic particles is much finer so wicking is more effective.  Worms will move in and out of this layer as the water cycles up and down naturally aerating this layer.


But above all the aim of the wicking bed is to provide a sustainable agricultural system.  Recycling waste material is adding fresh nutrients to the bed.  The micro-biological action improves plant growth.  Many plants rely on symbiotic fungi to help them extract nutrients from the soil.


The only disadvantage of using organic material is that is will gradually reduce in volume and will have to be topped up from time to time.


This can be done by simply digging a hole into the bed spreading the excavated material over the bed and filling the hole with fresh organic material. If the hole is dug in a fresh place each time the process can be repeated over and over again without ever having to remake the entire bed (as can happen with stones).


Another method is to have a compost bin with holes in the base so worms can draw the material down into the bed.  






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