Silicate clays cannot be chosen on the basis of silicic acid content only. A holistic examination of the specific elements contained in the clay determines the effects on the growing medium and the plants. These sheet silicates do not absorb great amounts of water, nor do they bind up elements in the soil. The best of this group are the aluminum silicates. Toxicity is possible with the sodium silicates or the magnesium silicates.
Silicates are a decisive factor in the healthy development of plants.
Not only for the silicic acid content, but also for trace elements, pH buffering, and enhancement of the microbial population in the growing medium. The evidence that silicon is of importance to plants is found in plants themselves. Research has clearly shown that readily available silicon plays a large role in growth, mineral nutrition, mechanical strength, resistance to fungal diseases, and adverse chemical conditions within the root zone. Plants absorb silicon in the form of silicic acid, H 4 SiO 4 . In soil environments silicon in this form is available in the same relative concentrations as K, Ca, and SO 4 .