Hi, welcome to GoY, I would suggest a mix of 2 parts ericaceous compost, 1 part sharp sand, and 1 part horticultural grit, Derek.

Thanks for the info.

I believe they like ash from the bush fires in Australia, do you think ash from burnt pine needles which are slightly acid would be ok in the mix?

Bill

HI, they like an acidic , well drained soil, so I don't think it will do any harm, but in Australia it's probably the only 'fertilizer' they get, but isn't really necessary in cultivation, Derek.