By Alanturk
Wiltshire,
United Kingdom 
I few years back I put a post on this forum about some Banksias that I had grown from seed. Apart from those I have given away, three have grown into decent-sized bushes, but one of them has died. It was in a different place from the others, so maybe that's part of the reason. I've cut it right down except for a few shoots near the ground that may survive, though I'm not expecting too much. I checked what I should be using to feed them and discovered I should be using a low phosphorus feed, but I can't discover exactly what that would be. I wonder whether anyone can offer me the name of a suitable proprietary product please. Thanks.
10 Jun, 2020
Answers
For our Proteas (including Banksias) we have previously bought phosphate-free "Trevena Cross Slow Release Protea Fertiliser".
See links from their (older) webpages here:
https://www.trevenacross.co.uk/garden/fertiliser/
(The Protea fertiliser is lower down on the page.)
https://www.trevenacross.co.uk/plants/restios-and-proteas/
Here are some other pages of interest:
https://www.kelways.co.uk/page/protea-care/90/
https://www.burncoose.co.uk/site/content.cfm?ref=Protea+-+Care+Guide#:~:text=Feeding,fertilisers%20which%20can%20be%20used.
10 Jun, 2020
the original question said they were Banksia [protea]
10 Jun, 2020
Most Banksias also need pretty sharp drainage.
10 Jun, 2020
when you say Banksia, do you mean proteas or banksia roses?
10 Jun, 2020