Fertiliser NPK Advice Needed Please

[Pat3222]

Here is a study if anyone is keen -
http://anpsa.org.au/articles/phosphorus-needs.html

I avoid P fertiliser on all my Grevilleas, though I think Neil makes a great point about developing a tolerance - I have Grevilleas growing below my citrus which I feed the crap out of. I’d be almost certain they get run off of the liquid fert and all the manure higher up in the same bed and they don’t seem to mind. They’ve been there since seedlings so have grown up with it I guess.
Cheers

[SteveW]

The proteacea family, which includes grevillea and banksia, develop specialised roots when grown in low phosphorus soil. This explains why seed grown plants fed on regular fertiliser from the start are fine, as are the grevilleas down hill of the well fed citrus.

As for the fertiliser companies, i wonder how long it will take them to add the word "some" to their labels saying natives need low P fertiliser . . .
My guess is I'll be compost before then.

[treeman]

3 cheers for Pat and Shibui for kicking the low phosphorous for natives BS into touch.

Even Gardening Australia repeated this BS a few weeks ago, along with several bonsai newsletters I read. The field tests proving most (80% plus) Australian plants were ok with phosphorus were done 20 years ago. Yet the myth persists. I suspect the fertiliser industry has a vested interest in selling native fertiliser, to go with their assorted, and virtually identical flowering, citrus, pot plant etc fertilisers.

Remember how Nurofen had different products for different types of pain until they were fined by the regulator for misleading advertising?

References:
http://anpsa.org.au/APOL8/dec97-4.html
http://sesl.com.au/blog/the-myth-of-p-s ... e-natives/

I killed a batch of Grevilleas several years ago with a fertilizer that was higher in Phosphorous.
So its not complete BS. It really does depend on the species you are growing

Of course it isn't. (total BS that is) Many plants show reduced growth with P levels much higher than that required for growth. Not just natives but things like azalea and holly. There are many. On top of that, for a long lived tree you want it to grow with a mycorrhiza and quite low levels of soluble P will inhibit that leaving the plant more susceptible. Certainly I would not use more than about 2% P on anything and then only if balanced with K. Maybe 3% on known P gluttons.
Too much P also interferes with Fe uptake. Note in the Handreck paper he talks about controlled release fertilizers with 0.9 to 1.3% (in other words, quite low) In most cases that's all you need.

[treeman]

So its not complete BS. It really does depend on the species you are growing

And what they have experienced before. I can acclimatise my banksias (which are usually very sensitive) to P and can use pretty much any normal P fertiliser on them but if they get a bit hungry they'll quickly start growing proteoid roots again and become P sensitive again.

Why not just give low P to begin with and be done with it?

[treeman]

The proteacea family, which includes grevillea and banksia, develop specialised roots when grown in low phosphorus soil. This explains why seed grown plants fed on regular fertiliser from the start are fine, as are the grevilleas down hill of the well fed citrus.

As for the fertiliser companies, i wonder how long it will take them to add the word "some" to their labels saying natives need low P fertiliser . . .
My guess is I'll be compost before then.

If those grevilleas are in the ground they probably will not see that P for a long time. It's is tightly held by soil and does not move through it readily.

[Pat3222]

Hey Mike, thanks for your input, some interesting points you’ve made. I don’t go out of my way to use high P fertiliser on any plants, let alone natives, though I’ve just got some Swamp Cypress and read 10:10:10 is ideal? I generally buy whatever is on special - Powerfeed, Charlie Carp, Osmocote etc and feed everything (bar the Grevilleas) with those per instructions on the pack. None of these are much higher than the safe P levels you mentioned, though some are much higher than “native”. I guess I just wouldn’t pay for a separate native fertiliser (or Nurofen haha) if the Grevilleas need a feed they can have half strength.

You mentioned it would take a long time for the manure and citrus feed to go through the ground to the the Grevilleas on the hill. My understanding (I’m no expert but keen to learn) of P toxicity isn’t that it’s poisonous to the native plant but inhibits the ability to absorb/use iron. Can you use iron chelate to prevent potential future problems or is it only effective as a cure?
Cheers
Pat