Many people garden successfully without ever testing their soil, but they are probably fortunate in gardening on ground that is not deficient in nutrients, is neither too acidic nor too alkaline, and receives plenty of nutrients anyway as part of normal cultivation. If things don’t seem to be growing well, a soil test is the best starting point for putting things right, and dedicated gardeners test their soil routinely once a year.
Professional soil testing is the most accurate for nutrients, but you can get a reasonable idea of the major nutrients in your soil with simple indicator kits. Testing for pH is quick and effective. (Bear in mind that kits vary from one manufacturer to another, so always follow the manufacturer’s instructions.)
The term pH is a scientific way of stating how acidic or alkaline something is. Soils vary in their degree of acidity or alkalinity. The scale goes from 0 (more acidic) to 14 (more alkaline), with 7 as neutral. Soils never reach the extremes, and horticulturally, 6.5 can be considered neutral in that it is the pH at which most plants will grow happily.
Acid-loving plants, such as rhododendrons, camellias, peonies and heathers, need a lower pH and may develop chlorosis (a yellowing of the leaves) if grown in chalky soil. Chalk-loving plants like dianthus and lilacs prefer a pH of 7 or above.
These differences may sound small, but on the pH scale 1 point represents a ten-fold increase in acidity or alkalinity.
Testing the pH: Collect your samples and mix with water as described for nutrient testing, but for the pH test you don’t have to wait for the mixture to settle, and only the test chamber is filled with the solution. Clean tap water is used for the reference chamber. Add the indicator chemical provided with the kit, then put the top on and shake vigorously. Compare the color with the shade panel on the container for the nearest pH value.
Adding Lime to the Soil: Never add lime unless you have tested your soil first and know that it is necessary. Too much lime applied regularly can be harmful for your plants. Always check that you are applying the right sort of lime at the appropriate application rate. Your testing kit should contain advice about how much lime (which will vary with type) to apply to your soil to adjust the pH.