The main causes of yellow leaves in bonsai are due to lack of light and lack or excess of water.
Make sure you apply the right watering technique.
- Insert your finger 1 cm into the substrate.
- If it comes out wet, we should not water.
- If it comes out dry, we must water. Irrigation must be abundant, that is, throughout the substrate and until the water comes out clean through the drainage holes.
Here you will find a video explaining how to do it:
Basic care for the outdoor bonsai
Another reason for yellow leaves on bonsai is the lack of iron and other nutrients in their substrate. For these cases we recommend the use of Ferrobonsai (iron chelate).
Leaves lacking in iron (chlorosis)
In the case of the Ficus retusa bonsai, it may happen that, in autumn, despite being an evergreen species, some leaves turn yellow and fall off. It is a normal process and we should not worry about it. This happens because the bonsai needs to get rid of the old leaf in order to make room for the new sprout.
Here are some articles below that can be of help:
Why are my bonsai leaves turning yellow?
How to water a bonsai
The 6 most common bonsai care mistakes
How to take care of your bonsai when on vacation