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The Care Of Sick Bonsai

Updated: Jan 7, 2023

If you practise the art of Bonsai at some point or another you are going to experience the decline of a trees health, This can have nothing to do with your experience in some cases but diagnosing the issue and making the correct adjustments can make all the difference to the tree. Even if a tree does not die after becoming ill this process can greatly slow down your trees development while you nurse it back to an energy positive state.

So lets go through a few steps on what to do when you notice the decline of a tree.

First we need to ask our selves a few questions about major changes in the trees environment such as;

1. Has the weather changed? I.E Summer has become very hot or winter has become very cold.

2. Has there been a lot more rain then usual over a few weeks?

3. Has there been an increase in wind exposure? ( especially hot wind on maples )

4. Is the tree being exposed to more sunlight then it might have been previously exposed too?

These few things can change a trees leaf characteristics or cause a tree to drop its leaves completely. If there has been a very obvious change in environment then this could be your issue, although a tree suffering shock from environment change is not necessarily bad for it, it can scare people when a tree suddenly drops all of its leaves or they change colour.

The next set of things we need to look for if there is no obvious environment changes is obvious damage externally to the tree such as;

1. Pests

2. Fungus

3. Broken or Cracked Branches or Trunk ( also keep in mind cracks can happen internally ).

4. Excessively Deep Wire Bite

5. Major wounds with Excessive bleeding ( caused by pruning at the wrong time of year ).

6. Soil Surface Compaction ( water sits on soil surface for sometime before draining through).

As you can see we are starting off with things that are very obvious as we dont want to work too hard if the answer is right in front of us, Pests are a very obvious problem to sight as you will see them on your tree. They can also cause a lot of damage to a tree if they have been on there long enough. The issue with pests is they usually attack weak trees so if your tree is being attacked you need to get rid of the pests but also concentrate on getting your tree back to a healthy state. With that in mind though this does not make healthy trees bullet proof to pests. An obvious sign pests are present on your tree is ants going up and down your trunk, usually they are harvesting what ever pest is on your tree.

Fungus can be a real issue when the weather begins to cool and can usually be avoided by a spray of lime sulphur at the correct dilution ( i use 20ml per 1L of water, others use higher at 30ml ). I spray all my trees at the beginning of winter and again a month later, this includes my benches to help kill of any spores that might be present. This will also help protect your tree from pests during the winter season.

Broken Branches can be fairly obvious as that single branch is the only thing on the tree showing poor health, you can usually trace it back to a healthy part of the tree and find the break. If one whole side of the tree is dying you may have an issue in the root system that is feeding that side of the tree, but if it is a single branch it is likely a break from wiring.

If you are to cut high sap flow trees during the active growing season they can bleed excessively losing a lot of their sap, If you do a few large cuts and open up some decent size wounds your tree can lose a lot of its energy in 1 hit so ask yourself if maybe this is something you have done?

And lastly soil surface compaction is a big issue for a lot of people and they don't even realise it. After watering a tree for a long time the surface layer of soil can break down and become very tight and compact which makes it very difficult for water to enter into the soil system, in this case the water usually drains down the side walls of the pot and it appears the tree is well watered as the water comes pouring out of the drainage holes. The issue is none of that water is actually making it into the centre of the root ball thus your tree is not actually being watered. This can sometimes be as simple to fix as using a root rake to rake the top layer off but sometimes this compaction can be cause by an overly root bound tree.

The next set of questions we need to ask ourselves dig a little deeper and those include;

1. Has the tree been watered properly?

2. Has the tree been fertilised?

3. When was the tree last re potted?

These 3 things can cause rapid changed in a tree, If a tree has missed a watering during an active growing season or high heat it can turn very quickly and corrective measures should be implemented quickly. Some trees more then others show signs of stress due to lack of nutrients such as black pines with yellowing needles and elms with yellowing leaves. Most evergreen species will show chlorosis in the leaves which is obvious when the veins of the leaf become very apparent. Both a freshly re potted tree and a tree that hasnt been re potted in a long time can show signs of stress, with a tree that has been freshly repotted you may have done it either at the wrong time or maybe taken too much off the root system. The aftercare for repotting is also very important so look at everything that has been done and see if you can draw a conclusion. With a tree that has not been repotted in a long time the root system might have stopped growing due to being root bound, if the roots stop growing the tree stops growing and if the tree stops growing it dies. This is why it is important to repot to give the root system a new space to continue to grow. A heavily root bound tree can become very compact and not take on water like mentioned earlier so this might be an indicator that there is an issue below the surface.

Now lastly i will list some common issues that you can also check which are;

Is the soil draining properly?

Is the tree in the correct soil? ( well draining, holds enough moisture )

Is the tree suffering from root aphids?

Is the tree getting enough unfiltered sunlight?

Is the tree away from objects that cause radiant heat such as tin fences or glass panels?

Is the tree being attacked by rodents such as mice, possums or birds?

These are just some of the first things to look for when a Bonsai starts to go south, Although this is not a complete list this is a good start to diagnose something that may have changed to give you somewhere to start making some adjustments. If none of these things are obvious or have changed you may need to bring someone to inspect the tree in person to give it a proper examination as problems are not always black and white unfortunately.

I hope this has been helpful to you

Until Next Time, Enjoy Your Bonsai Journey.

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Nov 13, 2021

Hi Josh, I'm in Mid North Coast and have two young english oaks in development. Each summer they both get severly infected with mildew covering most leaves. This season it is starting to appear again. Can lime sulphur spray help? The specs say it's effective against mildew but it would require application in summer, not winter. Cheers, sergey

Nov 13, 2021
Replying to

Lime Sulphur should be fine as long as you follow the instructions on the bottle. i would also start off by spraying one section of the tree first. I've had an instance where i sprayed all my trees in the garden for winter protection and all my Tea Trees dropped their leaves. Turns out natives don't like it too much. They all re flushed but it was a lesson learnt. i now spray one branch and leave it for a week now before applying to the whole tree if I'm applying to a species i haven't sprayed before.

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