Repotting a bonsai solo for the first time can be a challenge. Bonsai Bar will be offering repotting classes for people who have previously attended our workshops, and it is strongly suggested that these classes be taken for the health of your tree (and peace of mind). At our repotting classes, we’ll offer all the materials needed as well as the instruction for proper techniques and expertise in problem-solving.
If a prior attendee wishes to repot their bonsai by themselves, there are some guidelines to follow.
First, Bonsai Bar trees should not be repotted for at least six months of healthy establishment in their original pot. These trees will still be developing roots for months after a class.
For those that wait much longer, a year or more, there are signs that your bonsai will need to be repotted. The most obvious sign is lack of percolation of water down through the soil and out the drainage holes in the bottom of the pot. If the water seeps very slowly into the soil or cascades over the sides of the pot, there are so many roots in the pot that the tree is beginning to become pot-bound and will eventually “choke” itself to the point of dying. For those that choose to submerge or use immersion watering, the tree will very slowly produce air bubbles and the water struggles to fill in the rootball. Pot-bound trees will also show stress in the pads which will inexplicably weaken, turn yellow, and fall off. See our article on leaf-drop for more on pads falling off.
If the original pot is still desired for use, the original aluminum wire or zip ties anchoring the tree into the container should be cut from the bottom of the container. This should release the tree to pull free from the pot. If the tree resists, do not yank on the trunk or branches to extract the tree, instead, use a chopstick to pry up the tree, and/or use a butter knife to slide around the inside walls of the pot to loosen up the roots.
The rootball of your tree should look quite different from the initial potting of this bonsai. If healthy and given enough time, the roots should be a much more dense mat of fine feeder roots. If the rootball has fully expanded to the size and shape of the space inside its pot, the roots must be cut back to ensure the tree does not immediately become root-bound when put back in the container. One half to three-quarters of an inch clearance all the way around the rootball is a good reduction and allows for new root growth. The core rootball, if feeling like a brick more than a dense sponge when squeezed, might need to be loosened up through massaging with fingers or opened up with a chopstick as with the initial potting in the original class. Even if stepping up to a larger sized container for your bonsai, the rootball should still be broken up to prevent isolated compaction. If the roots feel slimy, smell of rotting wood, or are brittle and sparse, the tree needs to be watered less or more. Refer to our article on watering for information on watering methods.
Bonsai Bar trees that were initially potted using a mixture of pumice, lava, and potentially akadama, can recycle most of this substrate. Only the akadama or clay component will break down. Bonsai Bar trees that were initially potted with Diatomaceous Earth/DE might have more breakdown of the soil. Look for “dust” or “mud” as indicators of clay components that need to be freshened up. Similarly, any original organic soil that was trapped in your trees rootball might have also been denatured by the tree as it used up the nutrients, and also appear as “dusty”. This spent soil should also be replaced with new substrate. Purchasing new aggregate can be done through the Bonsai Bar website.
Depending on how your tree was anchored and what materials were originally used, there will be other components to replace. Containers that have plastic screens over the drain holes can reuse those screens. Pots that have a fiberglass mesh will need to have that mesh replaced (drywall mesh will work, as would plastic screens). Trees can be anchored with either bonsai wire or 10” plastic zip ties. For making it simple, it might be best to follow the same strategy that was originally used for rigging and securing these aluminum wires or plastic ties. All of these materials can be sourced from Bonsai Bar as needed.
As with the original workshop, add a base layer of soil into your container, re-anchor your tree firmly back into the pot, add more soil (new or recycled) over the top, and use a chopstick to push the aggregate into the roots and pot. The tree should be held tightly by both the anchors and the substrate. Push on the surface of the soil with your finger, there should not be any bounce to the surface of the soil, as that indicates air pockets below the surface.
Depending on the conditions, the tree should be watered (gently) as with the first potting, two or (no later than) three days after repotting. It is not recommended to place newly repotted trees in full Summer sun, nor subject them to undue stress such as colder temperatures. These trees will need a recovery period following repotting.
Please reach out to us with any questions. Trees repotted without the supervision of a Bonsai Bar class are no longer guaranteed.