For a completely different opinion, ph is relatively unimportant. Scientifically, ph is the measure of the number of H ions in comparison to the number of OH ions. If you have the same number of each, your soil will have a ph of 7. If you have 10 H for every OH, your soil has a ph of 6. If you have 100 H for every OH, your soil has a ph of 5.
So, if you have a low ph, it's because you have a lot of lonely Hydrogen ions waiting for minerals to attach too. Your soil is most likely low in calcium or magnesium, but could be potassium, sodium, or other trace minerals.
Write this down.......Low ph is not the problem keeping plants or trees from growing well, it is simply a symptom of the mineral imbalance that keeps them from growing well.
So get a soil test. An in depth test from Logan Labs is $30, and includes full details on the mineral levels available in your soil.
Here's what you're looking for.
Calcium - 68%
Magnesium - 12%
Potassium - 4%
Sodium - 1%
Sulfur - 75 parts per million
Iron - 100 ppm
Phosphorous - 75 ppm
Manganese - 60 ppm
Zinc - 8 ppm
Copper - 4 ppm
Boron - 3 ppm
Cobalt - 2 ppm
Molybdenum - 1 ppm
1 ppm is equal to 2 pounds per acre. So if your test says you're 10 ppm low on phosphorous, you need 20 pounds per acre.
A very good read, even if it's 10 years old now -
http://www.soilminerals.com/IdealSoilII.htm