Why is My Bonsai Turning Yellow? (5 Reasons)

If your bonsai tree is looking sick, you need to take prompt action if you want to save it. 

And yellow leaves are almost always a sign there is a problem. 

The most typical reason for a bonsai to start turning yellow is that it has been over-watered. 

However, other issues such as under-watering, the wrong light levels, and pests can also contribute. 

These are sometimes fatal problems, so you’ll need to investigate promptly to save your bonsai tree.

Keep reading to find out what issues yellow leaves could represent and how you can fix them.

5 Reasons Your Bonsai Is Turning Yellow

1) Too Much Water

Too much water is the most common problem people run into with their bonsai trees.

Many bonsai growers think their tree needs plenty to drink, but it’s easy to over-water a bonsai.

Because the pots can be quite small, the roots will be exposed to water whenever the soil is wet. 

So, the roots may not have much opportunity to dry out if you water your tree too frequently.

This problem can leave the plant unable to get enough oxygen and makes the tree vulnerable to root rot, which will turn the leaves yellow.

Root rot occurs when there isn’t enough air in the soil, and anaerobic bacteria start to grow, causing a foul smell and inviting decay.

And if your plant’s roots start to rot, it is in serious trouble.

But, it may be possible to save the bonsai if you take swift action.

To treat root rot, you will first need to tip the tree out of its pot and wash off its roots with fresh, lukewarm tap water. 

Then, using sterile scissors, cut away any roots that have turned brown or rotten. 

Next, allow the roots to air dry for a while. 

Afterward, put the plant into some fresh growing medium and re-pot it.

At this point, you can also remove any foliage that looks severely yellowed. 

Your bonsai should hopefully recover its fresh green leaves soon. 

You should then reduce how frequently you water the tree to avoid more problems with root rot.

Overall, you only need to water your bonsai when the soil has dried to about a centimeter under the surface.

2) Too Little Water

You may also be under-watering your plant.

Under-watering will usually lead to wilting leaves but can also cause yellowing, especially if the drought period continues.

So, you should keep an eye on how dry the soil in your plant’s container gets and water it if it appears to be drying out.

And if you let your tree get too dry, its roots will start to die. 

If the roots begin to die, it may take weeks or even months to recover.

Therefore, always make sure that you give your plant the appropriate amount of water that it needs to thrive. 

Furthermore, it is easy for the soil to get compacted, which can cause water to run down the pot’s edges rather than absorbing into the dirt.

This issue will leave the plant unable to access water, even if you regularly give it plenty to drink. 

Thus, you should always check to ensure the plant absorbs the water you give it.

If the soil doesn’t absorb the water, stand the pot in some water for ten minutes or so. 

This procedure should help loosen the soil so that it can soak up the moisture properly.

Finally, remember that some bonsai trees need watering more than once a day because their containers are so small. 

So, make sure you aren’t letting your bonsai get too dry.

3) Too Much Sunlight

It’s essential to know the preferences for your kind of bonsai tree. 

Thus, check whether your tree likes sun or shade before you decide where to put it.

Too much sunlight will cause your plant’s leaves to burn, which can cause yellowing.

It will also stress your tree out, so you need to avoid too much light by determining what conditions your plant likes and providing these.

To fix this issue, you can hang up a thin curtain to help reduce the amount of light your tree gets or just move the plant further from the window.

4) Too Little Sunlight

Too little light will also cause leaf yellowing. 

And most bonsai trees like a lot of light, so you need to ensure you provide those conditions for your plant.

Overall, it’s worth looking up the preferences of the specific kind of tree you are growing, but most bonsais like at least five hours of sunlight per day. 

However, the directness of the light they enjoy will vary.

If your tree isn’t getting enough light, it won’t produce the chlorophyll necessary to keep its leaves green, and the foliage will start to take on a yellow tinge.

If you notice this happening, try moving your plant closer to the window. 

You can also put a grow lamp near the tree to increase how much light it gets each day.

5) Pests

In some cases, a pest infestation can cause yellowing in bonsai trees.

Insects feeding on the plant’s sap will rob it of the resources it needs and cause stress, which will turn the leaves yellow.

If you notice yellowed leaves, you should inspect your bonsai tree closely for signs of pests.

The kinds of pests you are likely to see will vary depending on the type of tree you have, so it’s worth doing some research. 

But, keep in mind that common pests include aphids, spider mites, thrips, mealybugs, and scale insects.

So, inspect your tree closely if you think it may have an infestation. 

And most importantly, many insects like to hide underneath the foliage, so you should pay particular attention to the undersides of the leaves.

If you find insects, you can usually remove them with soapy water or neem oil. 

Yet, you’ll need to treat scale insects with alcohol to get rid of them.

Conclusion

Bonsai tree leaves can turn yellow for various reasons, so look out for these common issues. 

It’s also worth being aware that deciduous bonsai trees turn yellow in the fall, just like their full-size counterparts, which is a natural part of their cycle.

However, if yellowing occurs for no reason, you should act quickly so that your plant doesn’t die.