Root Over Rock Style...
Here, we will be examining the processes used to grow a tree over a rock (in the root-over-rock style) and create quite an effective bonsai. In this example, we will use Ficus Microcarpa over a Japanese Ibigawa Rock.
Bonsai is an art which in many ways (according to the artist's perception) tries to mimic the sights and processes seen in nature. To follow this, the 'root over rock' style has been widely used in bonsai. This is when the roots of a plant are made to 'cling' to and grasp a rock - spilling over it and eventually disappearing into the soil. This is to mimic when a tree has started growing in a small rock crevice (the seed usually deposited by birds) and has to use its roots to 'venture out' and find more nutrients once its major source has been depleted. As soon as the roots reach soil, they harden up and grow 'around' the rock - the roots now acting effectively as the tree's trunk.
Another instance of this happening in nature is when a tree actually starts growing on another and eventually overpowers its host by 'strangling it' with its roots.
This can be seen in the above photo, where a young strangling fig sends its roots down a paperbark tree into the soil to search for more nutrients.
Because figs are so tenacious and very well suited to the 'root over rock' style - I will use that species for this example.
The first step for a 'root on rock' style is to prepare the subjects. Both the plant and rock are important - so choose a suitable rock for this planting that looks appealing, attractive, natural and is a suitable size - but doesn't overpower the tree. More information on which rocks to choose - A fig will be used, so choose one that looks healthy and that has an extensive root system. What is essentially needed is a plant which has long, tough roots that you can 'drape' over the rock when you position it to create the effect that the roots have grown over and down it. If the plant does not have a very long root system (at least one and a half times the height of the rock you have chosen), plant the tree in a tall, yet thin pot to encourage the roots to grow downwards. A sawn off PVC pipe can even be used - as long as the correct alterations have been made. Grow the tree for a year or so, until the roots have grown long enough.
Materials needed :
Suitable Rock (Japanese Ibigawa Rock); Plant suited to root over rock style (Ficus Microcarpa); Plastic Grafting Tape; Scissors; Concave Branch Cutters; Bonsai Secateurs; Knife; Root Hook/Fork; Clean, Sharp Sand.
(1)
Once the roots are long enough, cut off all unsightly or unnecessary foliage and wash as much soil as possible away from the root ball of the plant - taking care not to damage the roots. (Try to remove as much soil possible by hand first - and then wash with a standard garden hose).(2)
Next, take your chosen rock and your plant and place the plant over the rock. From here, experiment, and see what arrangement looks best. Try to not place all of the roots to one side, as a bonsai should be able to be viewed from all directions. Find the interesting crevices, nooks and crannies of the rock and implement the roots of the plant into these - to make the finished bonsai look as natural as possible. You can even 'overlap' thin, undeveloped roots, which, if left long enough, will merge together.(3)
The next step is to set the roots in place. Although there are many methods - using grafting tape in my opinion is the easiest and most effective. (It is best to do this with an assistant). With one person holding the roots in place, wrap the grafting tape around the rock reasonably tightly, making sure to cover it completely except for the bottom, were the roots will protrude into the soil. Also make sure that there are no areas where roots can escape from gaps in the grafting tape where they are not supposed to be.(4)
After the roots have been set in place - making sure that all of the roots protrude from the bottom of the rock - bury it with the plant in a pot of clean, sharp sand. It should be planted so that no part of the rock is visible and the bottom part of the trunk of the tree is visible.(5)
Now thoroughly water the bonsai - leaving it in the pot for one to two years. Although the roots may seem small and weak now, in just one growing season they will really thicken up, and if you have placed them right - produce a really great show.
(6)
Here is the fig I used growing in a large pot after having been trained to grow over the rock (under the soil) for a period of 2 years. I usually leave figs growing for two years - just so the roots can really thicken up and attach themselves to the rock. If the plantis fast growing (or you're just impatient!) it is possible just to leave it for one year. If you do happen to take the plant out of the soil and see that it hasn't really developed properly, you can just repot it back for another year.