If you have sandy soil, you will be well aware of their difficulties in holding both water and nutrition. Gardeners who live in Perth are used to dealing with this issue, and every garden centre, soil and landscaping yard there will have bags and buckets of bentonite, as well as compost, manures, zeolite and other soil additives to help build a better soil.
A good loam soil is a blend of sand, silt and clay. A good garden soil has these three components plus manure, compost and humus. Then over time, the action of the living elements in the soil combine all these ingredients into the rich productive garden soil we all want.
So, to improve sandy soils or old landscape yard soils, which appear to have broken down and become tired and often described as ‘gutless’, you need the vital ingredient of clay. Clay is essential to forming good soil structure. Unfortunately it is often missing from constructed soils available from landscape and soil yards, and from sandy soils often associated with Perth and seaside suburbs. The bentonite particles coat the sand grains, allowing them to aggregate and form the cohesive structure so desirable in a good soil.
Gardeners can source clay in the form of Bentonite, sometimes marketed as ‘soil conditioner’ or simply as Bentonite clay. It is added to the soil in a dry granulated form. How much you add to the soil, and how you add it, depends on your individual situation.
• Newly constructed landscape and sandy soils: Add ½ to 3kg of bentonite per square metre, and dig evenly through the soil (the sandier the soil – the more bentonite). If you can, take this opportunity to also add zeolite, biochar, manure and compost. This is your easiest and best chance to get the soil right before you start planting. Now water the soil. This is essential, dry bentonite will draw the moisture out of the surrounding organic material unless you add additional water. Finally mulch the soil, even before you plant, mulching will help retain moisture within the soil.
• Established garden beds: Avoid digging into the plant roots by applying ¼ to ½ kg dry bentonite over the beds and water in over time. Repeat as needed.