Soil pH is referred to as the "acidity" of the soil and is measured by the number of Hydrogen ions present in the soil solution. Since S.W. Pennsylvania receives considerable rainfall every year, and since rain is H2O, soils tend to revert back to an "acid condition." Ammonium fertilizers also have an acidifying effect on the soil.

Soil Acidity and Alkalinity

When the soil pH is too "acid" (low pH) or "alkaline" (high pH), nutrients present in the soil become locked-up or unavailable. Correcting the pH has the same effect as applying fertilizer since it "unlocks" plant nutrients already present.

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pH

Description

Strongly acid

5.5 - 5.9 =

Medium acid

6.0 - 6.4 =

Slightly acid

6.5 - 6.9 =

Very slightly acid

7.0 =

Neutral

7.1 - 7.5 =

Very slightly alkaline

7.6 - 8.0 =

Slightly alkaline

8.1 - 8.5 =

Medium alkaline

> 8.5 =

Strongly alkaline

I am sure most of us already know this: Lime brings low ph up working slowly but last long term Vs. backing soda which also brings PH up quickly but doesn't last very long as it breaks down quickly.

Sulfer brings PH down works slowly breaks down quicker and is fair to good for the long term. Vs. magnesium where small amounts work very very quicly and can drop PH dramaticly for the very long term breaking down very very slowly.

Fun Fact:

I had to figure this PH stuff out during Hydrangeas 101 as the aim was Blue Hydrangea ( our 33 Blue Endless Summers have there own area named "The West Wall Garden" they are used for state wide showings ) with a well trained eye during judging the well known Hydrangea will tell all who look at em the real truth of any soil PH simply by the shade and coloring of the multi flowering heads.

Heres a link to read/confirm rain PH on the top portion of post:

http://www.donnan.com/soilph.htm