I wouldn't add the potash. I find the best way is to use the soil you have, but improve it slightly by digging in some compost and slow release low Phosphorus fertiliser. Grevileas (like most Australian plants outside the rainforest) thrive on very poor soils in the wild, so don't give them too much care or they may suffer.

Ned Kelly is very similar to Robyn Gordon and hybrids of this group are not too fussy about soils and fertilisers. While it's true that they need little if any phosphorus, you don't often see one obviously suffering from a surfeit of major elements. Pos02's advice is sound, but as soon as growth is well established it will probably respond well to a bit of blood and bone, Dynamic Lifter, or suchlike.

Thank you both very much. Would Blood and Bone be consided a slow release, low phosphorus fertiliser, or is there something else. Do I only apply it the once, at the time of planting, Thanks again.

M - It's not a good idea to use Dynamic Lifter near Natives as it will kill them off really quick. Yates who make this product near us, recommend it not be used also.
There are numerous slow release products on the market for Natives with a low P rating, these are what you should be looking at.
I noticed on another posting you have high acidic soil, which is something you should look at with Grevillea forms, maybe a handful of Dolomite dug into the soil below where you intend planting and then using some good quality potting mix in the hole and plant into this.

Also with your Robyn Gordon, have you thought about pruning it back to older wood to make it re shoot.

Here is a link that might be useful: Yates Products

compost is also a great low nutrient fertiliser for natives. as others have mentioned above, natives are used to poor nutrient soil but a nice top dressing of compost each year and a little mixed into the planting hole with the existing soil does them a lot of good without overdoing the nutrients.

I don't know a lot about blood & bone and it's effects on gardens, but I do know it is commonly used on lawns and exotic gardens. Grevileas tend to thrive on neglect, other than an annual prune and removal of dead flower spikes. I personally wouldn't use it for this reason, but if you are willing to try, give it a go on one plant to see what happens. Worst is you will kill it and need to replace it. I just add compost once per year to the base of the plant (do this for most plants), and the grevilleas in particular are all very healthy.

justcoreas' advice is sound, with a highly acidic soil, I'd try to bring the soil at least around your planting hole as near as possible to neutral ph, around 6 or 7. A bit of blood and bone is ok around natives, including grevilleas, but I'd only use a little. Whenever I plant a new native - and I've dozens of grevilleas thriving - I only use a sea weed /fish fertiliser. Seasol (seaweed concentrate) is good. I'd also be wary of native slow release fertilers, they're only suitable for some natives.

These grevilleas are decidedly fond of acid soils. Blood and bone is probably the best fertilizer, very slow release and good encourager of natural biota. Its the way to go provided you don't overdo it. Too quick a growth on grevilleas seems to result ih a short life.