Harvesting steam to get distilled water turns out to produce ample for the purposes of soil testing and we tested a couple of spots at the end of last week. The back of the back garden showed a medium green — weak alkaline — and the middle of the front garden actually looked a touch orange — weak acid — although it looked a little greener later in the evening. Possibly there is a lot of alkaline in the chalky lumps but it is not well integrated with the soil and takes some time to dissolve.
What I really need is a list of cheap and quick-growing plants which have specific requirements and thus serve as biological indicators; if they thrive, more expensive and cosseted plants can be safely planted. Perhaps certain “weeds” could fill that role (although I have a feeling dandelions are pretty tolerant of soil conditions).