In order to maintain the giant sequoias in a container for the many years that is required to achieve perfection in bonsai a combination of correctly performed topping and pruning must be done. The giant sequoias in the wild live in a root-bound state for their entire existence of 3000 years. The roots are self pruning. The soil in the natural groves of sequoias is often shallow with underlying granite bedrock. A mature giant sequoia requires about 1 acre of earth to spread roots capable of sustaining the enormous weight of up to 3 million pounds. Within that acre are many sequoias competing for the same space. Eliminating a root-bound condition is not necessary for the continued existence of the container grown sequoias but it is necessary to encourage significant new growth. The lack of space for new roots will create a condition where the plant must abort roots and then replace them, as they decompose, with new feeder roots. This will result in retarded growth. To best encourage new growth plant the tree in a larger pot. Once the tree reaches the desired size only time can create a gnarly ancient looking specimen.
The giant sequoia must never be bare-rooted. The woody roots of the sequoias send out white feeder roots that are necessary for nutrient consumption. The feeder roots are very brittle and will break at the slightest touch. The feeder roots are lost if the specimen is bare-rooted. Without the feeder roots the tree must rapidly regenerate new ones in order to survive. The tree will be seriously damaged if the feeder roots are removed. The most likely outcome will be death by dehydration in a month or more depending on the outside temperature.
The image at the top right shows the proper technique for root pruning a giant sequoia. This technique should only be used to reduce the size of the root ball so that it can fit into a smaller pot. A very sharp knife is used to slice the root-ball just as one would slice a block of cheese. Most of the feeder roots are on the bottom and sides of the root-ball. The bottom of the root-ball is never sliced. If you must reduce the height of the root-ball the material is removed from the top of the root-ball.
The image at the bottom right shows the top of the root-ball being shaved with a small knife to lower the height and clean up old small roots that have been exposed by water.