Why pH Is ImportantSoils are known as “sweet” if they are alkaline and “sour” if they are acid. Values of pH 7.0 indicate a neutral soil; above pH 7.0 is alkaline and below pH 7.0 is an acid soil. Most soils are within a range of highly acidic pH 4 to alkaline at pH 7.5 to 8.
If you wish to grow plants not suited to the pH of your soil, you can change the pH. You can make acid soil more alkaline by adding lime. Slightly acid soils can be made more acidic by adding peat, iron sulfate, or flowers of sulfur. It is, however, more difficult to lower pH in an alkaline, lime-rich soil than it is to raise pH.
pH is important in plant growth because it affects the availability of plant foods and prevents the spread of soil-borne diseases. Check it regularly, at least twice a year, as nature tends towards the acid side.
Working with your soil, not against it, will help you achieve more successful results. Any changes you make in pH should be small in scale, 1/2 to 1 point in either direction at the maximum. Don’t try to go straight from a 4.0 soil to a 7.0 soil in one season.
Raising and lowering pH is not an exact science and most plants have a reasonably wide tolerance, certainly to within 1 full pH point. Check the lists of plant pH preferences below and you will see that the majority can manage well on a pH of around 6.5… and many have a wide tolerance for different pH levels. But there are also many plants that only thrive in a very narrow pH range, so if your plants aren’t as healthy as you think they should be, you should check their pH range.
You can check the pH ranges for the following:
Flowers, Ornamental Trees & Shrubs