Help! White Fungus On My Bonsai Tree

I recently got a comment from a reader asking for advise about the fungus on his bonsai tree and how he could remove it. Mould is really not easy to treat so I’ve been doing some research and put together a guide on how to remove fungus from a bonsai tree.
White mould on a bonsai tree is mainly caused by over-watering. The excess water in the soil will clog the oxygen pockets, leading to roots dying and getting broken down by mould. Although very dangerous to the tree, it can be treated using a variety of techniques involving repotting and fungicides. Keep reading for a step by step guide to removing the white fungus from your bonsai.

The Causes Of Fungus

The main cause of fungus on a bonsai tree is over-watering. Soil usually has small air pockets which the roots use to get oxygen, as this is something they need to survive. When you are over-watering a bonsai over a long period of time, these air pockets are going to be full of water, essentially choking the trees roots. Now that roots are dying, they start getting broken down by mould and this is what infects the whole bonsai tree with fungus.
Although this is not the root cause of the problem, sometimes people leave pruned foliage to sit on the bonsai soil instead of removing it straight away. The pruned foliage is going to also get infected with mould and add to the spread of the fungus, as seen in the image above.
I would personally recommend investing in a good quality watering can and possibly a watering wand too, so as to avoid over-watering whilst you’re actually watering the tree. sing a watering wand enables a really fine water spray which is useful for watering bonsai trees gently. Click here to purchase a watering wand from Bonsai Boy of New York– it’s great quality, at an even better price and I’ve found it really helpful when I purchased it myself.

How To Treat Bonsai Fungus

photo of green leafed bonsai plant on brown potMany people will only notice the fungus on a bonsai tree once it has become a very serious problem. The best thing to do with a fungus infected bonsai tree is going to be taking it to a specialist at a local bonsai nursery as they’re going to be able to diagnose the specifics and show you exactly what to do for that mould type. If you don’t want to take it for specialist advise, there are still a few steps you can take in the hope of saving the bonsai tree.
Step 1 – Isolate the infected tree from the rest of your bonsai collection, you don’t want to take any chances of it spreading to other trees.
Step 2 – Remove the bonsai tree from its pot to really see the extent of the damage to the root system.
Step 3 – Prune off all the infected roots and any fungus infection branches you can see on the tree. The most effective way to get rid of fungus is first to remove it from the tree.
Step 4 – Repot the tree into a clean bonsai pot with a new bonsai soil mix. For more information on how to create a bonsai soil mix, see my article here.
Step 5 – Spray the tree with a Fungicide, following the instructions on the bottle. This is to kill off any remaining fungus that wasn’t removed during the repotting process.
I would suggest going over to Bonsai Boy of New York, which is where I purchase my fungicide. Here’s a fungicide I’ve used myself many times, in both an 8oz. and 16oz. size. It’s safer to use than most fungicides on the market and works on most common fungi. It’s been easy to use and effective in getting rid of any fungi that’s grown on my bonsai tree.
If you’ve purchased a Fungicide without a spray top feature, you might want to get a spray bottle in order to get a really fine mist over the tree. Click here for a link to a spray bottle! They’re really useful things to have around, should you want to spray your bonsai with anything that requires a more gentle mist.
This is the only chance you have to treat fungus on a bonsai tree, without seeking the help of someone with professional experience. If the infected tree is just a young untrained bonsai, I would give it a go trying to treat it yourself. If the fungal infected bonsai is an aged, trained tree I would most definitely advise seeking advise from a local bonsai nursery and seeking help from them.
green and brown broom beside blue and black motorcycle

Preventing It Happening Again

As bonsai trees are living in such a small container it’s very easy to over-water them frequently. The soil being constantly too wet is the main cause of bonsai fungus and root rot, so how do we stop over-watering? The key is to push your finger about an inch into the soil, and check to see how dry the soil is before watering – if it’s still moist or wet, then it doesn’t need watering. This simple tip should help you always avoid over-watering your bonsai. I have an article here talking about the 5 must know tips for watering a bonsai tree, which you may find useful.
When my bonsai tree got fungus, I stopped using the fertilizer I was using and stopped over watering it, letting the soil dry out much more between watering. I’ve been combing through the forums and it seems this has also had good results for other bonsai owners, so the combination could really prevent the fungus coming back. It’s hard to say if the fertilizing actually played a role in preventing the return of the fungus but if you are frequently using fertilizing it could be worth having a break and seeing the results.

Relevant Articles – Creating A Bonsai Soil Mix // Have I Over-watered My Bonsai?

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