Root over rock – how to

How to create a root over rock bonsai tree.

A young tree which has not yet produced lignified inflexible roots can be encouraged to cling to a rock in the following manner.
Select a stone that is perhaps a little deeper than the vision originally suggests because some of it will remain below the potting medium surface.. I have found tufa rock less than ideal because it will disintegrate over time, due to the effects of rain and frost. A textured rock with grooves running down over it would be ideal.

At re-potting time, select a container which will accommodate the rock completely. A tall plastic plant pot is suitable in view of what follows.

Wet the rock thoroughly and drape the immature roots over it, following any furrows or grain in the rock. Some of the roots should reach beyond the base. Secure them by binding firmly (not too tight) with previously soaked raffia which will rot away eventually when its function has served. Anything else might disturb the roots when being removed later. Put a layer of free- draining medium in the base of the container and set the tree bearing rock upon it. The spaces between rock and container wall are then filled gently with more medium until the whole rock and up to the original soil surface of the tree are covered. Water thoroughly and top up the medium to fill any space left by settlement.. Do not feed for three weeks by which time it is hoped that some bud burst or growth will be seen. Then resume your normal feeding and watering care as before. Trimming of the parts above the surface may take place during the growing period but don’t disturb the roots during that year.

In the following spring as growth again starts, cut away a section of the plastic container at the top and remove a similar depth of medium to expose the higher roots. A half inch might be right dependant on the size of the tree. This may be repeated at intervals during the next two growing seasons until most of the rock with the clinging roots is exposed.. There will be feeder roots around the bottom of the rock and underneath it in the layer of medium put below it at the start of the operation. By this time it will probably be appropriate to re-pot into a suitable bonsai pot, treating the rock and tree as one individual entity and allowing the feeder roots to spread laterally into the shallow but wider container. The roots by now will be holding the rock firmly and have assumed a more mature appearance imitating the colour and texture of the trunk bark.

This may seem to be a long drawn-out procedure but bear in mind that the tree parts above ground will have been continuously monitored and trained as any other bonsai.