Facts on Soil Acidity and Alkalinity

A pH of 7 is neutral, neither acid nor alkaline. A pH higher than 7--such as 8 or 9--means that the soil is strongly alkaline. A pH less than 7 marks the soil as acid, around 5 quite so. A simple home soil test kit can be purchased in which you match the color of an indicator solution against a chart for the pH reading. Electronic devices that do this are also available.

Most plants do well when the pH is between 6 and 7, just a shade on the acid side. Most North Coast soils are naturally slightly acid and in this range. If your soil shows an extreme pH, it is best that it be brought close to this desirable range--at least for most plants.

Liming is the usual way to correct extreme acidity, or to make the soil "sweeter." The safest material to use for this is ground-up limestone rock, called agricultural lime. However, hydrated lime can be used. On a light soil, 50 pounds of ground limestone per 1,000 square feet should raise the pH about one unit, as from 5 to 6, but 75 to 100 pounds might be needed on a heavier soil for the same effect. It is best to take a pH test in order to determine whether liming is needed or not.

The other side of the coin is acidification of soils that are too alkaline. This is not normally a problem in this area. However, if needed, 40 pounds of agricultural sulfur per 1,000 square feet should reduce the pH nearly a point.