How to repot your Bonsai
Not sure if your bonsai tree needs to be repotted?
It is pot-bound
Roots are growing out of the drainage holes, or the root mass forms a dense, winding mat around the edges when lifted from the pot.It is a young, fast-growing tree
Young trees building their trunk structure often need repotting annually at the beginning of the growing season. Mature bonsai need repotting only every two to five years depending on the species (deciduous trees generally require repotting more frequently than conifers).The soil has degraded
Over time, granular soil breaks down into fine dust, clogging drainage holes and choking off oxygen to the roots.It is planted in the wrong soil type
Trees from standard retail stores often arrive in dense peat or field clay, which easily leads to root rot. Full repotting to fix poor soil should wait until early spring for temperate outdoor trees, though tropical indoor species can be repotted year-round (if kept under grow lights if you live in a place with dark winters).
While healthy trees benefit from having their roots trimmed during a standard repot, avoid aggressive root pruning if your tree is weak or struggling from being in bad soil. Instead, gently remove bad soil, trim only dead or rotted roots, and plant it in fresh substrate to let it recover.
What pot should I repot it into?
In growing bonsai, you'll use a combination of techniques to keep the tree small. The idea is that both the tree and the pot stay compact regardless of the plant’s age. This means you need to prune the branches, but also regularly trim the roots to make room in the pot for new growth.
Since growing bonsai is equal parts art and horticulture, you might want to change the pot to better complement the tree. If you think the current pot looks good and suits the plant, re-using it is perfectly fine and is actually the most common approach.
Traditionally, specific guidelines exist for choosing a pot. The thickness of the trunk base correlates to the depth of the pot, while the tree type (such as coniferous versus deciduous or flowering) determines whether a glazed or unglazed pot is suitable. While these rules are helpful, you don't need to follow them blindly if you don't want to. Choose what you think looks best. It’s your tree, after all.
There is also a major difference between a "finished bonsai" and a tree early in development. For trees in training, the goal is to thicken the trunk and branches quickly. These plants grow much better in larger training pots, planters, or even in the ground the first couple of years. This gives an expanding root system better chances of absorbing more water and nutrients. Only once the basic structure (trunk and main branches) is set is the tree ready to be planted in a shallow, traditional bonsai pot.
Recommended soil
A variety of soil types can be used when growing bonsai. Traditionally in Japan, three main volcanic substrates are used: Akadama, Kanuma, and Kiryu.
Akadama is a granular clay soil with excellent water and nutrient retention properties, as well as high porosity. However, it degrades with age, and its porosity slowly decreases as the tree grows in the pot. Younger, fast-growing trees in pure Akadama are often repotted every 1 to 2 years, whereas mature trees can go 3 to 5 years between repots. While Akadama is frequently used on its own or mixed with mineral aggregates, adding fine peat-based soil is generally avoided, as peat decomposes quickly and clogs drainage.
Kiryu is a heavy volcanic sand rock rather than a soft clay. It is primarily mixed into soil blends for pines, junipers, and other conifers that require excellent drainage and less frequent repotting. Because Kiryu is stone-based, it decays much more slowly and won't clog the pot like breaking-down clay.
Kanuma is a soft, pale-yellow volcanic substrate characterized by its high acidity and lightweight, sponge-like structure. Kanuma is traditionally used for acid-loving species. Most notably Satsuki azaleas, Camellias, and Rhododendrons, which develop chlorosis (yellowing leaves) or root issues in neutral or alkaline soils. Like Akadama, it degrades over time and requires periodic repotting.
Apart from these, alternative substrates that might be easier to find if you live outside of Japan include burnt clay granules, pumice gravel, and lava rock. These inorganic substrates do not break down as quickly and work well as substitutes. Just ensure the substrate you choose has a pH level and mineral profile that your specific tree species benefit from.
How to repot your Bonsai
Remove the pot
Unfasten any anchoring wires visible at the bottom of the pot near the drainage holes. Gently grip the base of the trunk and ease the tree out. If stuck, run a small sickle or knife around the inside edge of the rim, or gently tap the outer sides of the pot to release the root ball.Comb out the roots
Using a root rake or hook, gently comb out the roots starting from the bottom and working outward to remove old soil. Keep a spray bottle on hand to mist the roots continuously during this process, as exposed fine root hairs dry out and die quickly when exposed to air.Prune the roots
For a healthy tree, prune away 20 - 30% of the long, outer root mass to make space for fresh growth. Cut back thick downward-growing taproots to encourage a flat, radial root system. Skip root pruning if the tree is weak, sick, or being repotted strictly out of season.Secure mesh and anchor wires
Cover the drainage holes with mesh screens to prevent soil loss. Thread length sections of aluminum bonsai wire up through the bottom drainage holes. These will be used to secure the tree firmly in place later.Add base soil
Pour fresh soil into the bottom of the container, forming a small mound in the center so the tree isn't resting on a flat surface. Position the tree at a height that slightly exposes the tops of the main root flares (nebari), which adds visual maturity to the bonsai.Position and anchor the tree
Place the tree onto the soil mound, positioning it slightly off-center if you want to follow traditional aesthetic guidelines. Wrap the anchoring wires over the root mass and twist them tight to prevent wind or accidental movement from snapping new roots as they grow.Add soil
Fill the rest of the pot with soil. Use a chopstick or skewer to gently poke into the root ball in small circular motions, working the granules into every cavity to eliminate hidden air pockets. Tap the sides of the pot to help the substrate settle.Water
Water the tree heavily until the runoff exiting the drainage holes runs mostly clear. Fresh Akadama and Kiryu will release cloudy, dusty water during the first few passes, which is best to be flushed out so it doesn't settle and choke drainage.
After repotting
Repotting is stressful for any plant, especially for a bonsai whose roots have just been pruned. It is completely normal for the tree to pause active growth for a few weeks while it recovers.
During this recovery period, follow these care steps:
Keep the tree in a bright spot sheltered from harsh direct sunlight, heavy wind, and frost for 1 to 3 weeks. Wind and hot sun increase water loss faster than reduced roots might handle.
Do not apply fertilizer for at least 3 to 4 weeks after repotting. Fresh root cuts are sensitive, and fertilizing too soon can burn the new root tips. Planta will automatically pause feeding tasks for a safe period after a repotting task has been completed for the plant.