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Bonsai trees are ordinary trees that have been made into small trees by certain measures. To keep them small, they should be repotted regularly. But when should you repot the bonsai? We'll tell you the best time.

In a nutshell

  • Repotting important for bonsai health
  • generally repot after 3 to 5 years
  • Twisted growth of the roots as a sign
  • ideal time: early spring

Why is repotting important?

Repotting involves cutting back the roots and branches. Both are important for the health of the bonsai. Especially for

  • the oxygen supply in the soil
  • the acid balance of the soil

The reason for this is the small bowl of the bonsai. This takes root quickly. This leaves less room for air voids in the soil. These actually supply the tree with oxygen from the soil. The soil, which settles more and more over time, further reduces the number of air voids. In addition, dense and damp soil means that the carbon dioxide produced during cellular respiration dissolves in the water. Carbonic acid is formed. This gradually acidifies the soil. These factors lead to

  • Shortening of the distance between the leaf nodes on a shoot
  • short term: better flowering
  • brakes on growth
  • death of the bonsai
With old bonsai trees, you can delay the time of repotting a little

Notice: With old-looking trees, this can underline the character. Therefore, the time of repotting these bonsais should be postponed by another year. But the longer you wait to repot, the more difficult it becomes.

Ideal time for repotting bonsai

In general, between 3 and 5 years are estimated as the ideal time to repot a bonsai. However, this is not universal. It also applies:

  • transplant young plants after 1 to 2 years
  • older bonsai with slow root growth 1 to 2 years longer than regular
  • Bonsai in rapidly decomposing substrate faster than trees in structurally stable soil

The decisive factor for repotting is not how long the tree has been in the pot, but how compacted the soil is. So check once a year by taking your bonsai out of its pot. If the roots grow in a circle around the ball (rotary growth), you should repot the bonsai soon. If the roots are still in the ground, you can wait another year. Other signs of compacted soil are:

  • Tree grows slower than typical
  • Soil hardly absorbs any water when watering
  • Root ball pushes up out of the shell

But there are also other times when it makes sense to repot the bonsai:

  • new purchase
  • Mold/algae formation
  • diseased leaves despite watering and ideal location
  • Salinization of the bonsai soil (e.g. after over-fertilization)
  • excessive pest infestation
If your bonsai has too many brown spots, repotting it can help.

Notice: Don't repot your bonsai just because one of the points is met. Observe the plant growth closely and then weigh up whether repotting is really necessary. Too frequent repotting can also have disadvantages.

When should you repot bonsai?

For almost all bonsai species, early spring is the ideal time to repot. In Germany, this corresponds to the period from around the end of February to the beginning of March. It is important that the following criteria are met:

  • Permafrost over
  • not too warm yet
  • Tree just before budding

Then the bonsai is still in hibernation. Meanwhile, he survives the repotting better. In individual cases, mainly with conifers, bonsai are not repotted until the end of summer. By then, however, the midsummer heat should already be over. In summer, you should only repot in Europe if absolutely necessary. In addition, the bonsai must then be placed in a greenhouse for a few weeks to grow.

Notice: In Asia, some tree species are repotted after flowering (May to June). This is not a problem there because of the high humidity. However, this is not recommended in Germany.

Bonsai trees are best repotted in spring.

Be careful not to repot the bonsai at the wrong time. This has a negative effect on the growth of the bonsai:

  • too early: slow healing of the interfaces
  • too late: water and nutrient supply suffers
  • too frequent: no/poor regeneration of the roots

frequently asked Questions

Can I repot and cut the bonsai at the same time?

Yes, that is even recommended. Shorten roots and branches if necessary until the tree is the desired size. This is how new, short, fine roots grow, which improve the absorption capacity of the tree. In addition, the root system becomes more compact.

Do I have to fertilize the bonsai after repotting?

No. The first fertilization should take place after four weeks at the earliest. Before that, the bonsai draws the nutrients it needs from the new soil. However, since it is susceptible to pests after repotting, you should not expose it to direct sunlight or draughts. A shady, sheltered spot is ideal.

Do I need a new pot for the repotted bonsai?

Perhaps. In principle, the bonsai is adapted to the pot, not the other way around. Therefore, the old shell can usually be used again after cleaning. The bonsai should be as flat and small as possible. A new pot is only a good idea if the tree has grown much larger or smaller and you want it to stay that way. In general, the length of the bowl should correspond to about 2/3 of the tree height.

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Garden plants