I'm +1 on the pH meter. We can find a double probe meter for $12 at home depot where you take some soil and put it in a cup of water and then stick the meter in there. It will give a fairly accurate reading within a tenth or two of a point. Most of the worst alkaline soils are only around 8 pH which is just 1 point over neutral I would think you would only hay a slight reaction with the vinegar, but would still not know how much to compensate. Another good thing to test at the same time is the water you would use to water your plants. If you are using well water or "city water", in many areas that can be around 8. Someone cancompare all they want with the soil, but of they don't use a neutral water, they can have the same problem.
