Banksia Leaves Curling

[BonsaiPancake]

Everything seemed fine a few weeks ago, but this poor guys leaves have started to harden and curl, plus lose a lot of colour.

Some of the branches seem a little 'soft' (still hard, but just not like normal). No fertiliser through winter, and usually just PowerFeed pellets and PowerFeed/Seasol liquid through the growing season. It's in a pond basket, so typically drainage is excellent so hard to argue overwatering but I'm not an expert. I haven't looked at the roots yet, I thought I would ask here first.

I've had it for around 3 years and repot usually mid to late spring with no issues like this before.

Thanks in advance!

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[legoman_iac]

Not much experience yet with banksia ... but looks dry to me, no?

[Phil Rabl]

My banksias are often the first of my trees to need watering. I also wonder if your tree has dried out.

[BonsaiPancake]

With the warm and dry winter I could see it being dry, but my watering has still been semi-frequent. I wouldn't say the soil ever fully dried out, but it's definitely possible that I just didn't notice.

If this is the case, is there anything I can do to recover it or is it done for?

[shibui]

My first thought was also dehydration, especially when it happens with the first warmth of spring. I lost quite a few banksias at this time of year before I realised they grow roots so prolifically. After a year or 2 the roots are so dense that water just cannot physically penetrate the root ball so even with good watering the inner root ball is just getting drier and drier.
I note you repot mid spring which is good for banksia. Did this one get done last spring and, if so, how much reduction and replacement of mix?
It may not be obvious how tight the roots are in the pond basket.

[BonsaiPancake]

I note you repot mid spring which is good for banksia. Did this one get done last spring and, if so, how much reduction and replacement of mix?
It may not be obvious how tight the roots are in the pond basket.

I believe I did it mid-Spring last year, but possibly a little later due to it being extremely wet. From memory I would guess a 50%+ reduction in roots and added around 75% new mix in with 25% of the existing mix (my standard for most of my trees). It grew incredible well last Spring / Summer and was still pushing growth in Autumn.

I might give the roots a look over and grab some photos before deciding what to do with it.

[BonsaiPancake]

Some photos of the roots. Deeper into the root ball was damp. I gently raked some roots and they did fall off very easily. Lots of mycorrhizae-like clumps of roots too.

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[shibui]

Deeper into the rot ball is damp which should rule out dehydration.
I find banksia roots are very brittle so roots falling off very easy seems normal too.
Banksias don't usually have fungi association so Mycorrhiza - like roots may be proteoid roots? In which case fertiliser could damage the tree but I guess its unlikely you've fertilised this early in the season?

[Rory]

The look of your dying foliage and the soil, makes me think its simply overwatered. Often in overwatered Banksia, I find white fungus type growth that can sometimes be the visual start that something is wrong.

especially this comment: .... "Some of the branches seem a little 'soft'"
Banksia branches don't get soft from drying out... .thats usually overwatering or rot.
Low levels of sun will also make the situation worse.

Over the years of having Banksia, I have lost many more Banksia from being overwatered and developing rot.... than dying from drying out.
Rot can start in areas where it has thick heavy soil and not draining properly or the tree just isn't pulling water out of a certain area.
I've had many Banksia lose large masses of roots while the other half powers on like normal... but if you don't watch it, the rot can spread and the foliage will deteriorate. The branches eventually become spongy and darken as the rot grows inside.

Generally more than not, winter will then exacerbate the problem.

Banksia need incredibly good drainage, but more so all throughout the mix, not just beyond the roots. All the areas need to have water continually being pulled out of the mix so parts aren't staying damp.

[Phil Rabl]

While it is true that it can be difficult to tell if leaf damage is due to too much water or too little water, BonsaiPancake says the tree has "excellent" drainage and that his watering has been "semi-frequent", so it is hard to see how over watering can be the problem in this case.

If it were my tree I would water and fertilise normally and see where the tree throws new shoots when the growing season kicks in. Banksia can grow proteoid roots, so you need to manage fertilising. Here is a link to a thread that includes some information on fertilising banksias. viewtopic.php?t=27698

[Rory]

While it is true that it can be difficult to tell if leaf damage is due to too much water or too little water, BonsaiPancake says the tree has "excellent" drainage and that his watering has been "semi-frequent", so it is hard to see how over watering can be the problem in this case.

If it were my tree I would water and fertilise normally and see where the tree throws new shoots when the growing season kicks in. Banksia can grow proteoid roots, so you need to manage fertilising. Here is a link to a thread that includes some information on fertilising banksias. viewtopic.php?t=27698

Just because the poster says it is in a pond basket does not mean there isn’t a drainage problem within the mix. If you put slow draining mix in a pond basket, it’s still a slow draining mix. Together with the usual low lying sun and cold days of winter, it can add up to bad issues for a Banksia.

Not sure what semi-frequent means. What is important is whether the mix is still damp deep inside the soil when it is next watered, not whether it’s frequent or infrequent. Those terms are relative and don’t really mean anything in this regard. When I say Overwatering, I mean it is a term that doesn’t literally mean it’s been continually watered, but if the mix isn’t drying out inside the main ball of the mix, then it doesn’t matter how infrequent it gets watered, it’s going to be ‘overwatered’ as it hasn’t sufficiently dried out in the inner areas before the next watering.

[BonsaiPancake]

Thanks everyone for your input. I'll watch it closely over the next few weeks and see what happens.

Something came to mind worth mentioning - a few weeks ago I gave my trees a good spray of Neem Oil as I spotted some mealybugs. This Banksia was fine, but gave it a spray as a tree sitting next to it had them.

I only ever spray after the sun sets, but I wonder if that could be what's at play here? Like all my other comments, this isn't something new for my Banksia. I've sprayed it plenty of times in the past.

[BonsaiPancake]

Update on this - this tree and the younger Banksia sitting next to it are both pretty much dead. Slowly the leaves dried out and the branches went a darker brown / purple sort of colour. When cutting into some of the thicker branches, they were noticeably soft (not mushy though) and there was a dark green colour throughout.

I've chopped off anything dead and will keep them in the shade for a few more weeks before disposing of them, just in case I see a lower shoot or something.

So strange as just the Banksia's were affected. The bench it sits on also has a Casuarina, a Ficus, some citrus trees, and a few Bougainvillea's - all are unaffected and thriving at the moment.

[Matty7]

I lost a Banksia Serata quite a few years ago in a similar fashion.

I assumed it would have been bullet proof...

I'm going to try another one as I really like them. Might try growing it in a pot full of gravel

[BonsaiPancake]

Further update to this.

A Turkey Oak that is also in the same style pond basket and on the same bench, has also died.

That's now 3 trees lost over winter in similar circumstances and similar general care. I've carefully looked over the remaining trees in pond baskets (10 or so) and they all seem fine with recent growth or buds popping. For reference and in case anyone can see a pattern, the remaining pond basket trees are at least 1 of - She Oak, Bougainvillea, Tiger Bark Ficus, Lemon, Kumquat, Acacia, Ginkgo, Maple, Redwood, Silk Tree.

Side note: the two citrus trees did lose a significant number of leaves throughout winter, but have new shoots currently. Other citrus I have are doing fine (in regular nursery pots).

One more common occurrence with the Banksia's and the Turkey Oak is that I cut a few branches over winter off the Banksia's (not a full trim, but a few branches I didn't want to develop), and the leaves of the Turkey Oak went brown but didn't properly fall off, so I cut them off in mid-winter.

Thoughts on possible disease from unclean cutting tools? I was really leaning into an under-watering theory given the baskets, dry winter, and some windy days where I skipped watering - but I would have thought a deciduous tree like the Turkey Oak wouldn't be as susceptible.

I'm pretty gutted and concerned for my other trees as this mass die-off of reasonably established trees has never happened to me before.

Does any of this information lean more towards certain theories? All of the following seem like they could be a cause:
- under-watering
- over-watering
- fertiliser issue
- disease through unclean tools
- the plastic from the pond baskets leeching something poisonous?