Shibui, what are you feeding them? Normal osmocote will kill them. So will dynamic lifer type stuff. You need to be extremely careful with your feeding or even the p/mix you start with should be prepared for low P plants or they just drop dead!
Just a thought.
Thanks for the advice Treeman. I have been growing banksias for quite a long time. I've actually killed more by being frightened of feeding and repotting than from using the wrong fertilisers. I am using low P osmocote in the mix for all the banksias and adenanthos. Because the low P osmocote has a relatively short life they also need supplementary feeding or they do start to starve. Over the last 3 years I have found that chook poo pellets is actually quite good - still relatively low amounts but it does make a difference to the health and growth rates.
There is research that shows plants with lots of proteoid roots are sensitive to even low levels of P but you can desensitise them by giving regular small doses. The tree just sheds the proteoid roots and can eventually tolerate what we consider 'normal' levels of P. Plants that have been raised with P available do not develop many proteoid roots and can take much more fert than those raised with low levels of nutrients. I usually avoid giving the banksias high P ferts and only use low P on them but a few weeks ago I fertilised a tray of Tassie B. marginata seedlings with Thrive by mistake. So far no sign of any problems and they would normally be well dead by now if they were sensitive. That particular tray is among exotics and has been getting regular doses of whatever I am fertilising with so they have never developed intolerance.
I actually think that banksias show real potential as bonsai. They grow quite fast. They thicken dramatically, even in a small pot (a bit like figs). Tolerate quite severe root reduction (as long as it is in warmer months) and shoot prolifically from older and bare wood. In fact, all the attributes of figs but cold hardy along with all the rest. There must be a recipe for a great bonsai with all that going for them. Getting the shape right may take some doing but I have seen some excellent examples at Canberra shows. Grant Bowie is one grower who has some excellent specimens and a great deal of knowledge from many years experience with banksias.
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I had assumed the deaths were a result of the plants drying out, maybe even for a short period but I'm starting to wonder if this might be a result of fungal attack? The seed was collected from local trees - the inland form of B. marginata which some botanists have told me have some distinct differences from the coastal plants. I'd be interested to hear if anyone else has had similar problems with either coastal or inland or Tassie forms.
