I second that. I have a grevillea growing in a container - same situation with a P intolerant Australian native species - and I have only fertilized it once in its 6 years with me. Not a common practice with any container planting, as they typically need consistent periodic fertilization. But it is thriving and growing and produces copious blooms.

btw, the fertilizer I did use was fish emulsion, NPK of 5-1-1. The lowest P fert I could find other than lawn fert, which are usually P free.

If they really need fertilization (sounds like they might not from other posters comments) blood meal + wood ash for an organic approach or a lawn fertilizer for a synthetic approach

@Sara Malone My clay soil would probably be high in phosphorous (I guess most clay soil is). So I might be better just building a large mound of non-native soil or building a bottomless container that is 24 inches high and laying that on top of native soil. What would be good substrates for the non-native soil? I guess leucadendron like some acidity, so adding some redwood bark might help. Do any of these soils strike your fancy for this application?

I make a mound with a mix of about 60% amended loam (I try for as low a % of organic material as possible) anbd 40% 1/4" lava pebbles without fines. But if you see the comment from the UCB guy, eventually the roots reach the native soil (I"m adobe) and they croak. The biggest/oldest one that I have seen in the SFBA is at the Gamble Garden in Palo Alto, at about 7' tall and maybe twice as wide. My oldest is in the ground about 10 years. I had a beauty die last year - a 'Jester' that was magnificent, froze badly in the winter of 2013/14 and came all the way back and then some. I still plant them; they are fast-growing and very drought-tolerant.

@Sara Malone So you are taking a true inorganic sandy loam and making it even faster draining by adding lava? This is a typical loam I can buy here.

Would any compost be rich in phosphorous?

Would redwook bark be rich in phosphorous? If yes, how can we make the soil slightly acidic? What about peat moss?

What is the ideal pH for Leucadendron? I read they want pH below 6, but what about 4 to 4.5 pH, the level at which acid lovers like Azaleas and Rhododendron would thrive?