Thickening a Bonsai Trunk

It can take more than a decade to get the look of your bonsai right.

Growing bonsai is an art form for those with great patience. Even small bonsai trees take years to grow, just like their larger cousins. One of the most important elements of the bonsai art form is growing branches that are arranged in the most aesthetically pleasing form. However, the shape and thickness of the trunk is every bit as important. The trunk often catches the eye before anything else does. Before you try to develop the branches of your bonsai, you must first learn how to get the right thickness for its trunk.

Lower Branch Growth

One method of thickening your bonsai's trunk is to allow a branch near the base of the tree to grow very large. Because this branch is the first, the largest part of the nutrients remain at the base of the trunk instead of being sent up to higher branches. This configuration causes the trunk near the branch to receive extra nutrients as well, promoting faster growth than the upper portions of the tree. Once the trunk has achieved the diameter that you want, you can remove the lower branch if it does not meet your aesthetic requirements for the tree.

Growing Wild

Another method of thickening your bonsai trunk, meant only for deciduous trees, is to let it grow in the field or in a large pot for a few years before transplanting it to the small bonsai pot. The unrestricted space will cause it to develop a larger trunk more rapidly than it could in the bonsai pot. Once the tree has reached the desired thickness, cut the trunk at the height you want your bonsai to be, and transplant it to the bonsai pot. New branches will grow out of the trunk.

Extra-Thick Trunks

If you desire an especially thick trunk of 3 inches or more, do not try to grow branches until you have the right trunk diameter. This is a process that can take several years. If you have been growing branches for the bonsai, then by this point they will likely have gotten too thick for your finished product. Instead, you will have to cut away all the branches and just keep the lower part of the trunk.

Staking

If you are growing your trees in the ground to develop a large trunk, do not stake them. Unstaked trees have to deal with all the force of the wind themselves, and as a consequence they grower larger, stronger trunks.

References

• CalTech: Bonsai
• Northland Gardens: How to Thicken the Trunk of Your Bonsai
• Bonsai 4 Me: Developing Informal Upright Trunks for Deciduous Bonsai
• Evergreen Garden Works: Developing Large Trunks for Bonsai

Resources

• Texas A & M University: Bonsai