As far as silica goes it helps strengthen cell walls , builds up resistance to pests/pathogens and can help ease the burden of overdosing with nutes, Because most of the silicon in the plant’s crust is held in forms plants cannot take up. These include silicon dioxide (silica) and various silicate minerals. While plants can’t take up silica, they can take up another form of silicon —monosilicic/orthosilicic acid. Bacteria can convert other silicon compounds into monosilicic acid. However, this process takes weeks or months. By the time silicon is in a plant available form, the plant might be too far along in it growth cycle for the silicon to be of much value