Firstly, you need to find out what the pH of the soil is before you start trying to get it down to around 4.5-5; chemical pH testing kits are cheap and much more reliable than most electronic test meters available.
If your soil is very chalky you will have your work cut out trying to lower the pH, and would probably be better off lining the planting hole with perforated plastic sheeting and filling with ericaceous compost.
If the soil is already around neutral or slightly acidic you can
temporarily lower pH by using diluted vinegar, but a more long lasting fix involves mixing in sulphur chips to the top 6" of soil - soil bacteria slowly convert the sulphur into sulphuric acid which lowers the pH (I think this could reasonably be argued to be an organic approach, although I wouldn't expect everyone to agree with me!
)
Sphagnum peat moss is another good acidifier, but you might not want to choose that for environmental reasons.
Incorporating or mulching with acid-forming materials like pine needles can help, but it's worth remembering that nearly all fully composted materials finish up around neutral pH, so you will need to keep monitoring the soil pH levels to ensure you are doing enough.
If feeding, use ericaceous feeds, and use rain water rather than tap water (especially if your tap water is hard.)
Finally, don't obsess too much about getting the pH exactly right - last time I checked mine it was only just below 6, but my 3 bushes still crop well.
