AusBonsai

I put all my bonsai-to-be on auto-irrigation while I was away for a few weeks. One of the first I ever put in training was among those... and it has a much more substantial organic component in the soil mix than all the others. I’ve returned to find it clearly suffering from overwatering. Beyond returning to an appropriate water schedule, is there anything I should do to help ensure this tree survives? I’m quite fond of it, and it’s one of my more advanced ones. Thanks

OK -I'll have a crack but please wait for more knowledgeable folk. What follows is my gut instinct -- not an educated response.

If you have one of those hand held soil water meters (round $10 from Bunnings) - check how moist the soil still is.

Once it has dried out a bit, give a tonic by way of Seasol. Why? My instinct would be to assume a lot of good sh!t (that's a technical term) in the soil has been washed away or drowned ... and it won't hurt to re- replenish the goodness by way of a seasol tonic for the roots.

Now... please wait for more learned answers; I answered because I wanted to test my gut instinct.

What makes you think it’s been over watered?

Overwatering usually leads to root rot which is a fungal infection. You haven't mentioned what species is involved but I would try a root fungicide to try to control the infection. Hopefully the tree will have enough strength to overcome it.
I've heard others suggest repot and root pruning to remove as much infected root as possible to give the tree a chance to grow fresh, strong roots.
You have already reduced watering. The tree may just overcome it all by itself

Hi Dave
If trees have sat in water to long for whatever reason they will show signs of root rot
That's simple to check by carefully removing from pot and looking
If the mix is free draining overwatering or weeks of heavy rain will not be a problem.
What soil mix do you use?
When you add organic mater to mix do you sift well first, fines can cause water logging
I would trim any sick/rotten root tips you find back to living tissue if that is the problem.
That's what I did once when using strait potting mix/unsifted and most of my trees recovered
Then I repotted into a courser mix and now I sift everything that goes into my mixes

Thanks all for such prompt and helpful responses. I didn’t want to fill my first post with unhelpful detail, but I realise it was a little sparse.

The genus is graptophyllum, occasionally known as native fuscia I believe (along with many others - not a helpful common name). It was labeled as g. excelsa when I purchased it but I have a suspicion it’s ilicifolia - but that’s neither here nor there for this topic. I understand they like free draining soil though (says the guy with a root rot infected one )

Yes, root rot is the issue. Robb, you’re right, there’s way too much fines. My guess is that root rot was already an issue because the soil mix was crap, but now it’s strongly evident. The design has some exposed roots that are now trying to tell me it’s too waterlogged below and some browning leaves that had barely hardened off before I left.

So.. since the soil mix is crap and unlikely to facilitate the issue resolving itself... I guess I’ll repot and root prune to remove at least some infected roots and provide a more free draining environment. I worry about messing with a stressed tree, but leaving it feels like a worse idea. I suppose I should apply the root fungicide in this process, as suggested by Shibui? Is that a direct application or something added when watering after the repot?

Thanks again for the responses. Super helpful. Next purchase = sieves

I have no experience with the genus in question. But I have had many Bonsai die over the years from root rot.
The worst material to suffer were probably Japanese Maple, bougainvillea and lantana. Once the root rot was evident in the maples, it was usually too late. I didn’t have great success from rid-rot or other liquid rot treatments.

However, from native material I have not had as many problems. My first obvious recommendation is to grow material that is happy being in water logged mediums, or swamps etc. just make sure they get plenty of sun, and root rot probably won’t be an issue.

Having said that, I realize that is not helping your current specimen, but good to know if this one or others don’t survive.

From my experience when I have had root rot, I have had excellent success from shibui’s recommendation. With casuarina and banksia that suffered from root rot for example, the first step for me is always:

Repot, and get rid of all the old soil. Start with a fresh well-draining mix, preferably mixed with course rocks or ash about 0.5cm - 1 cm cubed.
Cut off any dead or rotting roots.
Going forward, only water it once the soil is almost dry. Don’t use an automatic watering sprinkler. For example, so far this October due to the intense rain we had, I have not watered my trees once this entire month. Each time I check or am approaching watering it forecasts rain and so I leave it until it is almost dry.

Gradually give it as much sun as the species can tolerate, but if it was kept in shade gradually move it each week into sunnier and sunnier positions.
Use a grow pot with a lot of drainage holes.
In winter, you can err on the side of caution and leave it longer when it’s drying out, as opposed to sunny summer days when it is risky to leave it. But this means you can afford to over water a bit in summer because you’ve not overwatered during the safer seasons.

More recently I have come to a conclusion that advice instilled in me from the 1990’s was to completely drench the soil once it starts to dry out, then allow it to almost dry out, and completely drench it again and repeat etc etc, as the normal routine. However, if you have a micro-climate that is constantly on the wetter side, this can do more harm often. I no longer “soak” my trees at watering time and instead only give a moderate watering more often rather than a one-off drenching and then leave until it dries out approach. This has considerably improved the roots and health of my trees. I was doubtful of this advice from a wholesale native grower, but since trying it, it seems to show greatly improved results.

And lastly, if you are having issues with mediums staying too wet too long, do not over-pot the tree. Try to ensure the roots make up about at least 70% of the pot or higher. There will be exceptions with some species yes, but not most.

Good luck.