I haven't used Rootblast (but I might now that I have read the website). From reading the website, I don't think it will help the roots penetrate the clay layer - you really need plants with strong tap roots to do that. What it might do for you is to increase the root network within the top soil and get more nutrient out of that. But it sounds like you are building a pretty rich and active top soil anyway. In your situation, I would focus on building the garden up and not worry too much breaking through the harder layer.
By the way, do you know if the silica pan is sitting on top of more hard clay or whether it is just a crust on top of looser soil? I just moved house and thought we had hard pan in the back yard - only to find that it is a 1-2 cm crust made up of clay and concrete dust from building the house. So once that is broken up with a pick, I think I can just mulch over it to get the soil going.
Thank you David, I think you are very right in saying that I should just build up the garden and not worry too much about breaking through to the hard stuff. That is exactly what I have been trying to aim for.
The pan is actually underneath the clay so I can only dig down so deep before I hit it however, like Earl has also mentioned about having raised beds & digging deep, again this too is what I am trying to achieve. I just thought that the rootblast was going to somehow miraculously break through the pan somehow.
Without rootblast, my veggies, flowers, shrubs & trees are growing rather well anyway which I believe is due to the compost I make & liquid fertilizers. I usually don't buy any commercial products for my garden as I am with the notion that if I can make it.....I do.
I'd go with David, raised beds rather than digging them in, but I would deep dig them first anyway to aerate the subsoil. I did that with my raised beds which have aerated Glen innes clay underneath, I think its been worth the effort.
Don't turn it over, just bury the fork and work ti to open up the soil and give your plants that extra space, air and drainage.
Also good cariovascular exercise.