Training Your Bonsai: How To Prune, Shape, And Maintain Your Tiny Tree

December 28, 2015

Shaping and maintaining your bonsai tree is known as “training,” and are the heart of the art of bonsai! Part two of our bonsai series will teach you how to prune, shape, and “train” your tree into an interesting shape and miniature size.

Once you have established a healthy plant following the guidelines in part 1 of our bonsai series, you are ready to begin the art of shaping, pruning, and training your tree. (We recommended waiting until your tree has had one full growing season to acclimate to life in a container before beginning any heavy pruning or shaping, as too much stress at once can harm or even kill your tree.)

Structural Pruning For Your Bonsai:

You will only perform this once in the life of your bonsai, but it will dictate the basic shape of the trunk and main branches, so approach this step with care and thought.

First, become familiar with the basic styles of bonsai – formal upright, informal upright, slant, cascading, multi-trunk, or windswept – and decide which best suits your plant.

Beginning in early spring, follow these steps:

  1. Place the tree at eye level and examine the tree from whichever side you decide will be the front.
  2. Decide on a trunk line. For example, if the natural trunk of your tree is arrow-straight, but you have your heart set on an informal upright style, select a branch on the upper third of your tree to be the new leader, and prune away the trunk above this branch.
  3. Once you have your trunk line, you are ready to select the main branches of your tree. There are a few basic rules about branch selection to keep in mind:
    • Remove all branches on lowest 1/3 of the trunk
    • Remove all limbs that hide or obscure the front of the trunk
    • Do not allow two limbs to grow at the same height
    • Remove disproportionately thick limbs from the top of the tree, maintaining thicker branches toward the bottom.
  4. Look at mature trees of the same species as your bonsai and try to mimic the spacing and quantity of main branches that occur naturally.
  5. Use proper bonsai tools, in this case as a concave cutter, to reduce the visibility of wounds and blemishes caused by such drastic pruning.

Branch Structure and Maintenance Pruning For Your Bonsai:

When structuring and maintaining your branches, the goal is to overcome your tree’s natural tendency to concentrate its growth toward its crown and outer edges, an effect called apical dominance. Left to its own devices, your tree will quickly grow out of proportion and lose its sense of age and scale. By pruning and pinching throughout the growing season, it is possible to create branches that both taper and bifurcate (called ramification), as would a natural tree. Follow these steps to structure and maintain your tree’s branches:

  1. Begin branch structuring in fall, when you can see limbs in detail, without foliage.
  2. Work systematically, from the lowest branches, up.
  3. Prune the lowest branches back, leaving 3-4 leaf nodes. Prune upper branches even harder, leaving only 1-2 leaf nodes.
    • Hint: Prune each branch just after (not before) the point where a new shoot is growing. This shoot will become new branch leader, maximizing taper and giving realistic movement to your branches.
  4. Now, the remaining branches can be wired, or “trained”:
    • Wrap bonsai wire in a spiral around the branch and carefully bend, “add movement”, to any section of the branch that is straight.
    • Make sharper bends at leaf joints, where trees naturally change direction.
    • If you hear or feel cracking, stop.
  5. Beginning in spring, flushes of buds will develop on your branches. Pinch out the most vigorous (apical) growth at the tips of each branch, diverting energy to inner and lower growth.
    • “Pinching out” is the technique of removing the new shoot from an opening leaf buds.
  6. Allow remaining buds toward the end of the branch to grow 2-3 leaf nodes before trimming back to the first node. Buds closer to the trunk, allow further development before trimming back to 3-4 nodes.
  7. Continue this same process of pinching out apical growth and proportionate trimming throughout the growing season, as new flushes of buds appear.

Root Pruning and Repotting Your Bonsai:

As with any containerized plant, there will come a time when the roots have grown to fill its container and you will need to move your bonsai into a larger container (such as a shallow bowl planter, which comes in a variety of sizes.)

In bonsai, repotting is only part of the equation. Roughly every two years, the roots of your tree must be pruned. This process sacrifices thick roots in favor of smaller feeder roots, encouraging a dense root ball that fits in a relatively small container. Follow these steps:

  1. Begin in late fall or early spring, when water and nutrients are in less demand.
  2. Lift the tree from its current pot.
  3. Gently comb through the roots with a ‘root hook’ to remove used soil and untangle the roots.
  4. Use a sharp pair of shears to prune back approximately 1/3 of the root bulk.
  5. Remove any roots that appear black, slimy, or decaying.
  6. Remove any roots that grow straight down, and encourage roots to spread radially from the base of the trunk.
  7. Prune back any thick or straight root to where finer roots are branching off.
  8. Once you’ve trimmed root ball, pour a shallow cushion of soil mixture into the new container and place your tree on top.
  9. Sprinkle soil mixture around the roots and, with a chopstick, work the soil into the gaps between roots.
  10. When you reach the top of the container, lightly pack down the surface and water thoroughly.

We hope you enjoyed our two-part series on bonsai gardening! For basic information on choosing your tree, container, and soil, read part 1 in the series.