Repotting conundrum

[melbrackstone]

I'm in Brisbane, where it's been raining off and on for the past 3 weeks or maybe even more. If not raining, mild and mostly overcast. Three weeks ago I root pruned a few trees, bougie and fig, and they've powered on, constantly wet and happy as pigs in mud. Two weeks ago I heavily root pruned an old buxus, which had filled the pot with new roots in less than 6 months. Same thing, happy as anything, with the rain keeping everything very wet. Then two days ago I dropped a Tiny Trev lilly pilly out of its pot, only to discover the base of the root mass was pretty much empty of soil, and no water had been reaching down that far, so I cut the roots back hard, and potted into as small ceramic. Only took off about 5% off the top. It's powering on too!

So here's the conundrum, I thought the idea was to wet the media when first repotted, then let it dry out quite a bit, cos the roots will then grow to seek out moisture...and yet, these trees are making a liar of that technique. Admittedly it's still mid 20's in the daytime, and rarely lower than 15° at night still...

Am I pushing my luck, or have I just been lucky?

[KIRKY]

Your lucky Mel perfect growing conditions, warm, wet and sun
Cheers
Kirky

[terryb]

So here's the conundrum, I thought the idea was to wet the media when first repotted, then let it dry out quite a bit, cos the roots will then grow to seek out moisture...and yet, these trees are making a liar of that technique. Admittedly it's still mid 20's in the daytime, and rarely lower than 15° at night still...

I think that advice might be suited to repotting dormant deciduous material, especially where the roots have been severely reduced. The trees are not using water, so if the soil remains very wet (soil mix plays a part here too) there is a chance of anaerobic conditions and rotting. If trees are actively growing, the soil mix drains well and the volume of soil to remaining root mass is not excessively large, I don't think you will have a problem.

[melbrackstone]

Your lucky Mel perfect growing conditions, warm, wet and sun
Cheers
Kirky

No sun Kirky, I know it's there, but it's been missing for weeks. It is still warm though.

I think that advice might be suited to repotting dormant deciduous material, especially where the roots have been severely reduced. The trees are not using water, so if the soil remains very wet (soil mix plays a part here too) there is a chance of anaerobic conditions and rotting. If trees are actively growing, the soil mix drains well and the volume of soil to remaining root mass is not excessively large, I don't think you will have a problem.

That makes a lot of sense, thanks Terry! I hadn't considered that part of the equation. Now I might go out and do some more repotting. Thanks!

[dansai]

Not to mention they are all very hardy plants. And rain water has many dissolved ions in it like oxygen and nitrogen. I keep all my plants fairly wet, I only really hold back water on my pines and cactus yet they have had rain more days this year than not. Everything is growing strong. Including the pines and cactus.

[shibui]

Are we confusing plants in the garden with plants in pots? I know the advice is to water deep but not often when putting trees in the garden to encourage roots to go deeper so they will be more dry hardy.
I have never heard anything like this for bonsai or potted plants. Roots have no real choice but to fill the available space in a container. I doubt that controlled watering will make any difference.
There is another guideline peculiar to bonsai that soil should be almost dry before watering. I believe this one stems from older soil based potting mixes and root rot. The idea of waiting until soil is almost dry in pots is to discourage fungal problems that can occur when roots are constantly wet. Root rot does not happen overnight, or even in a few weeks. It usually takes quite a long time of wet, low oxygen conditions for those fungi to grow enough to cause problems.

I doubt that a few weeks of wet potting mix will harm trees, especially when that soil is fresh and still drains really well so oxygen rich still. I'd actually say regular rain after repotting is probably good to kick start the plants again. The last thing very new roots want is a dry spell before they can harden off a bit.

[melbrackstone]

Not to mention they are all very hardy plants. And rain water has many dissolved ions in it like oxygen and nitrogen. I keep all my plants fairly wet, I only really hold back water on my pines and cactus yet they have had rain more days this year than not. Everything is growing strong. Including the pines and cactus.

No doubt they are very hardy plants, for sure. It's all so confusing, the information that we read and hear. I have made a habit of not keeping newly repotted trees very wet in the past, in case the roots didn't get enough oxygen, but this rain has been almost constant, so the mix, although very open, is just constantly wet. This is why I was worried, since I didn't want to have to bring the trees in out of the rain. Thanks for your help.

I doubt that a few weeks of wet potting mix will harm trees, especially when that soil is fresh and still drains really well so oxygen rich still. I'd actually say regular rain after repotting is probably good to kick start the plants again. The last thing very new roots want is a dry spell before they can harden off a bit.

Yes, the mix is fresh and very open, but the rain has been relentless, so there wouldn't be much oxygen in there, I don't think? Nevertheless, they do seem to be thriving, which was interesting to me, since I'd always thought that newly repotted plants should be kept on the drier side. Thanks for your input!

[dmattar]

No doubt they are very hardy plants, for sure. It's all so confusing, the information that we read and hear. I have made a habit of not keeping newly repotted trees very wet in the past, in case the roots didn't get enough oxygen, but this rain has been almost constant, so the mix, although very open, is just constantly wet. This is why I was worried, since I didn't want to have to bring the trees in out of the rain. Thanks for your help.


Yes, the mix is fresh and very open, but the rain has been relentless, so there wouldn't be much oxygen in there, I don't think? Nevertheless, they do seem to be thriving, which was interesting to me, since I'd always thought that newly repotted plants should be kept on the drier side. Thanks for your input!

I have no idea about the science behind it but I live in Brisbane too and I've recently repotted several ficus and some melaleuca seedlings in the middle of this rainy season with no ill effects. I used to be really scared when I first started bonsai a year(ish) ago because I got some root rot with heavy rainfall, compacted and water retentive pot mixes and bad watering practices. However, with my current soil mixes, I seem to have no issues. I have not moved any trees under cover this year except for the desert roses.

There are probably a few reasons for this - oxygenation being one of them. I also think that in the case of some trees with small containers and full canopies, very little water actually penetrates the soil compared to the amount of rainfall. Rainwater is also 1000000x better than whatever hardwater comes out of the tap for me which contributed to me not babying the plants anymore unless there was high wind. Having the open mix also increases your odds of having better outcomes.

[dansai]

Water moving through a pot pulls air into the potting mix. As long as there is spaces in the mix for air, which any good draining mix will have, there will be oxygen. Garden soil achieves this through its structure created by worms and microorganisms. Potting mixes should have this if they have good components and very little fines. I have always watered my newly repotted trees really well and have never had any problems.

[melbrackstone]

I'm so glad I asked this question, and appreciate the help, thanks everyone. I suspect the next week will be a challenge when the rain is pushed away by strong winds.

[Rory]

Anything I have repotted or in particular if I've cut roots off - I would never allow the mix to get dry for at least 4 weeks afterwards... ESPECIALLY with Eucs and Leptos.
I have lost many trees in the past - not from overwatering after a repot/root reduction - but from allowing the mix to get too dry within that crucial 4+ week recovery period. Because when new shoots appear, if they wilt from lack of water they can easily die off and then you can get bad die-back further too.

Going forward I personally allow the mix to get somewhat dryish (not dry) on the odd occasion, but if the top half is dry and the bottom half is slightly wet, I happily rewater. But the thing is, you can't control the rain or the elements, so they are naturally going to be re-watered often when the mix is still wet just from rain etc etc. In winter I happily allow the mix to go longer between waterings than over Summer. I find my trees do much better with occasional periods of drying off in winter.

Root rot usually starts to develop if the mix isn't draining well, or its remained constantly wet and logged for about 8+ weeks onwards. But if the mix is open and really draining well, I have even had Banksia in wet feet for months without an issue. But the main thing is, you must have a fast draining mix if you have recurring environmental problems like continual wet feet during winter etc. (My saviour is lots of washed river sand.)

[melbrackstone]

Cheers Rory, I'll take that on board.

[Ryceman3]

So here's the conundrum, I thought the idea was to wet the media when first repotted, then let it dry out quite a bit, cos the roots will then grow to seek out moisture...and yet, these trees are making a liar of that technique.

Hi Mel,

I think the concept you are alluding to in the above quote is one that I have heard talked about when it comes to conifers (specifically pines). I don't think the same applies to tropicals, and definitely not for our natives (in general). Too much water is not enough for the majority of natives I have ( various mels, leptos, casuarina etc) ... and I subscribe to the water tray after repot on most of these to maximise "soakage". I assume given tropicals go through wet/dry seasons in their natural environment - lots of water isn't an issue for them either.

As with just about everything in bonsai ... "it depends" is the start of almost every response to a bonsai related question!

[melbrackstone]

As with just about everything in bonsai ... "it depends" is the start of almost every response to a bonsai related question!

Got that right Ryan, I am certainly learning more and more every day. Thanks!