AusBonsai

Hi
I know its a difficult question but here it is anyway.
Anybody got any ideas on my banksia problem.
The bigger one sits in full sun and the two smaller get a bit of arvo shade. The big one possibly has had to much water as I have been concerned with trees after losing a few after that 47 degree we had here in syd 8 weeks ago.
The other trees in the same area and similar size seem fine.
The 2 smaller I found were very dry last week so gave them a soak untill bubbles stopped, seemed fine and noticed yesterday they are also looking sick.

All are under the carport now. In shade.

Any ideas???

Cheers Ben

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Banksias can be affected by several problems which all seem to end up with them looking the same as this so unfortunately I cannot accurately diagnose the problem.
Soaking the pots was correct but the damage may already have been done. Often they seem to look Ok for a week or 2 after the event.

1. Phosphate toxicity. If you have not fed your banksias much they will probably have developed proteoid roots which are designed to gather all traces of phosphate from poor soils. If you give them normal doses of fertiliser when there are proteoid roots they can overdose and die. However you do need to feed all trees in pots, even natives. I have killed more natives by not fertilising than ever died from too much. If in doubt, use a low P fertiliser but most natives are quite happy with any normal fertiliser.
2. Dry. Even though we think of natives as able to cope with dry, in pots, very few really can. I've lost quite a few that got too dry, usually when I was frightened of repotting natives just in case they di not respond well. Banksia roots are very fine and grow fast. After just a single year the pot is so full of roots that it is almost impossible to water properly. I have also seen them come back after losing leaves from dry so don't throw them out until December just in case
3. Phytopthera. This is a fungal disease that affects the roots of many plants. Banksias are quite susceptible to it. WA species are even more susceptible. A root rot fungicide may help but if phytopthera is the problem it looks like it may be too late.

Thanks Shibui.
The smaller ones were repoted in Oct and i feed my natives the same liquid fert as all others. Nitrosol and charli carp alternately. And natives get Bush Tucker feed instead of Scots osmocote the rest get.

Thanks for opinion. I will spray with seasol once a week and hope for the best i guess


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To grow a healthy plant we need to keep in mind the following. When repotting, make sure you arrange the roots so that they enter the new mix immediately. That means as many outward facing root ends as possible. Leaving too much of the old mix can be a huge problem if the original mix is much finer than the new mix. This sets up a condition where the root ball stays much wetter than the surrounding mix and as you water thinking that the pot is dry, it might in fact be very wet. A perfect situation for root rot to set in. Next, don't over pot. The new roots should start touching the sides of the pot within a matter of days or a week or 2 at the most. If there is no root activity the mix becomes stale. It's not exactly clear what happens but it probably has something to do with the soil biota. Once this happens, roots will avoid it and slowly perish. Strong swamp type trees will handle it but certainly not banksias which often grow in sand. After the plant is established (say 2 or 3 months) the medium should dry out every day. If it stays wet something's not right. So it's important to match the root ball with the pot - and the expected growth for that season. Generally, you get best growth if the distance between the cut roots and the inside edge of the pot is between 1 and 3 inches, no more. (25 to 75mm) 1 inch for slow plants and 3 for fast growers. This general information is applicable to most plants and you can vary it as you gain experience. Having a finer new mix than the original is much safer than the other way round. I repotted some B integrifolias which were sown last autumn into 75mm tubes this spring. They are still in the tubes and very tall and healthy. They dry out completely every day. Sometimes in less than 24 hours. This is the kind of situation you want with all your plants. If they are drying out every single day they are healthy. It's a good guide. The tubed plants will now need to go into something bigger, less than 1 year after sowing the seed. In short, you want the potting mix to be used and not just sit there waiting for the roots to enter it. This is fundamental to understanding horticulture. It works every time with everything from native trees to orchids to cacti and everything in between.
I would cut my losses with those banksias and start again but this time pot them into smaller pots using a finer sandier mix. If they grow faster than you expect, you will know what to do!

Well I just learnt a lot - Great info here Mr Treeman. thanks

Great info Treeman, I know now that I overpot most of my plants..from tubes into six inch squat pots is my norm.

Ben

Whilst the problems mentioned above may occur, mostly problems with Banksias as bonsai result from the belief that natives do not like to be kept wet. This is far from the truth!!!

In general Banksias grow best when their roots stay wet all through summer (say from 1 Dec. to the end of march in Sydney) . Growth will be massively increased and they will stay healthier. Your trees definitely show that they are suffering from too little water in summer. However in winter they do not need to remain wet.

Dennis Mc

Thanks Treeman and Dennis.

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