I have always loved root over rock bonsai, and thoroughly enjoyed researching and developing the process that grew the narrow leaf ficus pictured above. I have broken down some of my process below. I welcome feedback and questions so that everyone has the opportunity to continue learning.
This Ficus salicaria, narrow leaf ficus, was started from a cutting and grown on in a pond basket for about two years. The pond basket helps provide air pruning of roots to eliminate circling roots within the container, and they are not expensive at all. In this image you can also see the rock before the roots were grown over it.
At this point I pruned and wired the ficus to build the initial structure of the tree, while also working to complement the rock the tree will be grown on.
The pond basket does work very well to eliminate circling roots, but there were still some. I made the decision to use a supper roots container, which is pricy but works incredibly well and comes in many sizes. Because all roots are air pruned as they reach the edge of the container no rooting energy is wasted on circling roots. This builds an incredibly ramified root mass, in this case all around the rock placed in the supper roots container.
The ficus was bare rooted in order to place the roots over the rock in desired locations. I use grafting tape to hold the roots to the rock, and a few steel wires with rubber padding to hold everything in place. Once the repot was done I placed the tree in a humidity tent to allow the roots to recover. This works by drastically reducing transpiration which allows some photosynthesis to happen with little or no water loss.
I repotted the tree every June to prune excessive roots, and further train and hold young roots to the rock. I have already pruned many roots in this photo, and as you can see the rooting is very vigorous.
It is important to allow the foliage and top growth to grow freely, as the foliage and roots like to maintain a balance between each other. Look at all of the root choices to use to continue training the roots on the lower half of the rock!
This ficus is now 6 years old, and grown from a 6 inch cutting. I plan to show it this year, and welcome any feedback or comments. Thanks for taking a look at some of my techniques.