@Amy Gardner , I spent a little time on the 'bay.au and I found that Jiffy brand has some garden mixes that are buffered. I managed to get a soil engineer from ProMix (Premier) on the phone one day, and he was more than happy to fill me in on their mixes. Perhaps you could find a similar guy at Jiffy. There's also a garden vendor called The Climbing Fig that might be helpful about soils, etc.