As said, I use Actisil, which is meant as a foiliar spray. It contains silicon in the form of stabilised orthosilicic acid.
I tested it also on my clones.
I had 2 Cloners.
One sprayed with Actisil and the other cloner just water.
I could see significant better results with the clones sprayed with Actisil. (Anecdotical evidence!)
So it looked as it does not only builds stronger roots.
As I understand it, silicia reinforces cell walls. It helps the plants to withstand diseases, drought and heat.
This is a test done by an
institute.
And this is also a nice
read.
In the professional market there are silicia products that are meant as foliar spray and others are for irrigation.
There is a really big price difference in it.
I am told you can use the foliar spray silicia also in irrigation (but it is to expensive for that)
But the irrigation silicia can not really be used as foliar spray, because this silicia form is much harder to absorb by the leaves.