3 Root Pruning Pitfalls to Avoid during Bonsai Repotting

Pruning roots during repotting is a concern for every bonsai enthusiast. Proper root maintenance and pruning will do wonders for your tree. Root pruning serves two main purposes. One is to promote healthier root growth while the other is a more aesthetic reason, to sit in a nicer pot. To promote healthier roots, cutting and removing rotting roots is necessary. Spreading out the roots will also prevent roots from becoming root bound as root bound trees will start to stress and grow slower. The tap root, or the larger main root on the tree may require cutting as well. This is typically done to fit shallower pots. Below are three common mistakes we've found that can be avoided easily and lead to higher success rates.

Mistake 1: Not Balancing the Bonsai Roots with the Foliage

How much is too much? Luckily, many species of trees can handle aggressive root pruning. This characteristic is why they are commonly used for bonsai. These include common species such as Junipers, Black Pines, Maples, and many Tropicals. Aggressive cutting when done during the cooler seasons will not harm the bonsai tree too much. However, just remember that the tree you are supporting above the soil should somewhat match the tree below the soil. So when figuring out how many roots to cut, you will want to consider the balance between the bonsai roots and the foliage. If you've made large cuts to the top, it's safe to make large cuts to the roots as well. For younger trees, this usually doesn't pose a problem as the trees do not have a larger tap root to contend with.

However, sometimes you will have a larger bonsai tree that you would really like to place into a shallower pot. For many species, a large tap root cut will still be successful if done at the right season. However, there is always an inherent risk that the tree will not survive if the structure of the secondary roots and hair roots are not strong. For many of us, this is a risk we are willing to take in order to see our tree in the exact bonsai pot we want. That is why it is common for larger bonsai trees to be trained for many years in a very good soil mix to develop the secondary roots. When it is time to make a larger cut, the bonsai roots are so healthy that the risk of failure is minimal.

"Luckily, many species of trees can handle aggressive root pruning. This characteristic is why they are commonly used for bonsai."

Mistake 2: Letting the Roots Dry Out

Take care of your bonsai roots both while above and below the soil. While repotting, it is important to work quickly to prevent the roots from drying out. The longer the roots are exposed to the air, the higher the chance of the roots drying out and not surviving during the repot. Some tricks include keeping a spray water bottle close by to spray the bonsai roots occasionally while working. You can also put a damp cloth around the roots to maintain the moisture in the roots.

Mistake 3: Shifting Roots in New Pot

Lastly, once your bonsai tree is in the new pot, it is important to not let your roots move around too much. This will make it more difficult for the roots to establish in the new soil. To prevent shifiting, you'll want to make sure that you wire the tree into the pot. This is more essential when working with larger trees in smaller pots. Also make sure to fill in all air pockets to ensure that no moisture is lost around the roots.

"Take care of your bonsai roots both while above and below the soil."